^l\is  Book  is  the  property  of  t^e 

OfDanfornm   aDoHege   of   Ph^i^macg 

(  department  of   ^itartnacu   of  the 
Ifiniocrsitti  of   California  ) 


f^iresented   bn 


M^JJ_ 


Bate 


e 


._„,,„,,  Cotlege  of  Pha""*^"^ 


Digitized  by  the  Internet  Archive 
in  2007  with  funding  from 
■     IVIicrosoft  Corporation 


http://www.archive.org/details/elementsofchemis02grahrich 


** 


LIBRARY 


OF 


ILLUSTKATED 

STANDARD  SCIENTIFIC  WORKS 


VOL.   XIII. 


GRAHAM'S 

ELEMENTS   OF   CHEMISTRY 
VOL.  IL 

C&!!fbrri!a  Co!!:^c:o  of  Pharmacy 

NEW  YOEK: 
CHARLES  E.  BAILLIERE,  290   BROADWAY. 

LONDON:  HIPPOLYTE  BAILLIERE,  219  REGENT  STREET. 

185t. 


Entered  according  to  Act  of  Congress,  In  the  year  1857,  by 

CHARLES    E.    BAILLli:RE, 

In  the  Clerk's  Office  of  the  United  States  DUtrict  Court  for  the  Southern  District  of  New  York. 


W,   B.  TlN»ON,  rBISTBB   *SD  STSRBOinf PER, 

4<t  &  45  Centre  St. 


ADVERTISEMENT. 


The  present  Volume  completes  the  Work  as  a  Treatise  upon 
Inorganic  Chemistry ;  and  it  is,  accordingly,  furnished  with 
an  Index  of  Contents,  which  applies  to  both  volumes. 

From  the  time  which  has  elapsed  since  the  first  publica- 
tion of  these  Elements,  an  amount  of  alteration  and  addition 
had  become  necessary  for  properly  completing  a  new  edition, 
which  precluded  the  Author,  with  his  present  engagements, 
from  undertaking  the  task.  In  these  circumstances,  he 
gladly  availed  himself  of  the  assistance  of  Mr.  Watts,  who 
has  supplied  a  large  amount  of  new  matter,  including  the 
Supplement,  and  has  edited  the  volume  throughout  in  the 
most  careful  and  conscientious  manner.  The  most  con- 
spicuous changes  now  made,  by  which  the  work  is  improved, 
are  the  following  :  — 

1.  The  systematic  introduction  of  the  best  processes  for 
the  separation  and  quantitative  estimation  of  metals  and 
other  important  substances,  in  addition  to  the  description  of 
their  properties  and  reactions.  The  new  methods  of  volu- 
metric analysis  are  detailed,  with  the  description  and  applica- 
tions in  particular  of  Bunsen's  General  Method. 

2.  In  the  Supplement,  in  which  the  subjects  treated  in 
the  first  volume  are  resumed  and  brought  down  to  the 
present  time ;    The  determination    of  the   most   important 

A  3 


VI  ADVERTISEMENT. 

Physical  constants ;  viz.,  the  Mechanical  Equivalent  of 
Heat ;  the  relations  between  the  .  Chemical  and  Magnetic 
effects  of  the  Electric  Current,  and  the  reduction  of  its 
force  to  Absolute  Mechanical  Measure;  also  the  Measure- 
ment of  the  Chemical  Action  of  Light.  The  Polarisation  of 
Light  is  treated  in  sufficient  detail  for  the  wants  of  the 
Chemical  Student,  attention  being  especially  directed  to  the 
methods  of  Optical  Saccharimetry,  and  to  the  very  remark- 
able relations  between  Crystalline  Form  and  Molecular 
Rotatory  Power  discovered  by  Pasteur. 

3.  The  modern  views  of  the  constitution  and  classification 
of  Chemical  Compounds  are  explained  at  considerable 
length,  chiefly  according  to  Gerhardt's  Unitary  System. 
This  includes  the  classification  of  Organic  as  well  as  In- 
organic Compounds,  as  indeed  every  general  system  of 
classification  must  do.  In  the  same  portion  of  the  work,  the 
formation  and  reactions  of  the  principal  classes  of  organic 
compounds  are  explained,  so  far  as  appeared  necessary  to  the 
general  understanding  of  their  mutual  relations. 

4.  The  last  portion  of  the  Supplement  contains  the  most 
recently  discovered  facts  relating  to  the  Non- metallic  Ele- 
ments, and  the  Metals  of  the  Alkalies  and  Earths,  a  pro- 
minent place  being  assigned  to  the  allotropic  modifications  of 
certain  elements;  viz..  Boron,  Silicon,  Sulphur,  Selenium, 
and  Phosphorus,  and  to  the  methods  of  obtaining  the  alkali- 
and  earth-metals  in  the  free  state. 

THOMAS   GRAHAM. 

Royal  Mint  :  December,  1857. 


CONTENTS 


THE    SECOND    VOLUME 


METALLIC  ELEMEWrS  — (continued). 


ORDER  IV. 

Metals  Proper,  having  Protoxides  Isomorphous  with 
Magnesia, 


Sect.  I. 

Manganese 

Sect.  IL 

Iron 

Sect.  III. 

Cobalt 

Sect.  IV. 

Nickel 

Sect.  V. 

Zinc 

Sect.  VL 

Cadmium 

Sect.  VII. 

Copper 

Sect.  VIIL 

Lead 

OR! 

)ER  V. 

Page 
1 
23 
59 
74 
81 
89 
92 

111 


Other  Metals  Proper,  having  Isomorphous  Relations  with  the 
Magnesian  Family. 

Sect.  L  Tin  ...  130 

Sect.  II.        Titanium  .  .  .  145 

Sect.  III.       Chromium        .  .  .  152 

A  4 


Vlll 


CONTENTS   OP 


Sect.  IV.  Vanadium 

Sect.  V.  Tungsten 

Sect.  VI.  Molybdenum 

Sect.  VII.  Tellurium 


Page 
172 
176 
185 
194 


Sect.  I. 
Sect.  II. 
Sect.  III. 


ORDER  VI. 

Metals  Isomorphous  with  Phosphorus, 

Arsenic 

Antimony 

Bismuth 


203 
221 
239 


ORDER  VII. 


Metals  not  included  in  the  foregoing  Classes, 

tvhose  Oxides  are 

not  reduced  by  Heat  alone. 

Sect.  I. 

Uranium 

251 

Sect.  II. 

Cerium 

261 

Sect.  III. 

Lanthanum 

268 

Sect:  IV. 

Didymium 

273 

Sect.  V. 

Tantalum 

277 

Sect.  VI. 

Columbium  (^Niobium)     . 

285 

ORDER  Vlll. 

Metals  whose  OtXides  are  reduced  to  the  Metallic  State  by  Heat 
{Noble  Metals). 

291 
328 
346 


Sect.  I. 

Mercury 

Sect.  II. 

Silver 

Sect.  III. 

Gold 

THE   SECOND   VOLUME. 


IST 


ORDER  IX. 

Metals  in  Native  Platinum. 

Sect.  I. 

Platinum 

Sect.  II. 

Palladium 

Sect.  III. 

Iridium 

Sect.  IY. 

Osmium 

Sect.  Y. 

Rhodium 

Sect.  YI. 

Ruthenium 

Page 
363 
384 
391 
399 
406 
412 


SUPPLEMENT. 


Heat. 

Expansion  of  Solids 
Expansion  of  Liquids     . 
Specific  Heat 
Liquefaction 
Latent  Heat  of  Yapours 
Tension  of  Yapours 
Conduction  of  Heat 
Mechanical  Equivalent  of  Heat 
Dynamical  Theory  of  Heat 


421 
423 
427 
430 
431 
433 
440 
444 
449 


Light. 

Polarisation  .  .  .  457 

Change  of  Refrangibility  of  Light :  Fluorescence  481 

Spectra  exhibited  by  Coloured  Media  .  486 

Measurement  of  the  Chemical  Action  of  Light  489 


CONTENTS   OF 


Electricity. 


Page 
Measurement  of  the  Force  of  Electric  Cur- 
rents ....  497 
Ohm's  Formulas  .  .  .  499 
Electric  Resistance  of  Metals  .  .  502 
Keduction  of  the  Force  of  the  Current  to  absolute 

Mechanical  Measure                    .                  .  506 


(JHEMICAL  JNOTATION  ANI 

>  Classificat 

ION. 

Atoms  and  Equivalents 

509 

Gerhardt's  Unitary  System 

. 

513 

Types  and  Radicals.  —  Rational  Formulie 

521 

Classification    of  Compounds 

according 

to 

their 

Chemical  Functions 

527 

Water-type 

530 

Hydrochloric-acid  type 

548 

Ammonia- type 

553 

Hydrogen-type 

563 

Relations  between  Chemical  Composition   and 
Density. 

Atomic  Volume  of  Liquids  .  .  569 

Atomic  Volume  of  Solids  .  .  582 


Relations  between  Chemical  Composition  and 
Boiling  Point. 

Boiling  Points  of  Alcohols,  Fatty  Acids,  and  Com- 
pound Ethers  .  .  .  583 


THE   SECOND   VOLUME.  xi 


Chemical  Affinity. 

Page 

Influence  of  Mass  on  Chemical  Action            .  586 

Mutual  Decomposition  of  Salts  in  Solution  591 
Decomposition  of  Insoluble    Salts   by  Soluble 

Salts  .                 .                 .                  .  597 
Chemical  Decomposition  explained  by  Atomic 

Motion                .                 .                 .  600 

Diffusion  of  Liquids. 

Diffusion  of  Saline  Solutions  .  .  604 

Decomposition  of  Salts  by  Diffusion  .  613 

Diffusion  of  Salts  in  the  Soil  .  .  615 

Osmose. 

Passage  of  Liquids  through  Porous  Earthenware  616 

„  ,,  „        Membrane  620 

Physiological  Effects  of  Osmose      .  .  623 

Diffusion  of  Gases  through  Porous  Septa        .  625 

Development  of  Heat  by  Chemical  Combination. 
Heat  evolved  in  the  Combination  of  Bodies  with 

Oxygen  .  .  .  .625 

Heat  evolved  in  the  Combination  of  Bodies  with 

Chlorine  .  .  .  630 

Heat  evolved  in  the  Combination  of  Acids  with 

Bases      .  .  .  .631 

Heat  evolved  in  the  Combination  of  Acids  with 

Water    .  .  .  .632 

Calorific  Effects  of  the  Solution  of  Salts  in  Water      633 
Cold  produced  by  Chemical  Decomposition    .  635 


an 


CONTENTS    OF    THE    SECOND    VOLUME. 


NON- METALLIC  ELEMENTS. 


Page 

Oxygen  and  Hydrogen     - 

638 

Nitrogen 

651 

Carbon 

658 

Boron 

667 

Silicon 

672 

Sulphur 

.679 

Selenium 

688 

Phosphorus 

690 

Chlorine 

702 

Bromine 

711 

Iodine 

712 

Fluorine 

719 

Bunsen's  Met 

hod  of  Vol 

umetric  Analysis 

722 

Metals  of  the  Alkalies  and  Earths. 


Potassium 

Sodium 

Ammonium 

Lithium 

Barium 

Strontium 

Calcium 

Magnesium 

Aluminium 

Glucinum 


729 
732 
736 
741 
744 
746 
749 
753 
756 
761 


ELEMENTS 


0» 


CHEMISTEY. 


OEDEE  TV, 


METALS  PROPER  HAYING  PROTOXIDES  ISOMORPHOUS 
WITH  MAGNESIA. 


SECTION   I. 

MANGANESE. 

Eq.  27-67  or  345-9;  Mn. 

This  element  is  found  in  the  ashes  of  plants,  in  the  bones  of 
animals,  and  in  many  minerals,  of  which  that  employed  in 
the  preparation  of  oxygen  is  one  of  the  richest.  The  black 
oxide  of  manganese  was  long  known  as  magnesia  nigra,  from 
a  fancied  relation  to  magnesia  alba ;  but  was  first  thoroughly 
studied  by  Scheele,  in  1774,  and  immediately  afterwards  by 
Gahn,  who  obtained  from  it  the  metal  now  called  manganese. 
From  its  strong  affinity  for  oxygen,  and  the  very  high 
temperature  which  it  requires  for  fusion,  manganese  is  one  of 
the  most  difficult  of  all  the  metals  proper,  to  reduce  and  fuse 
into  a  button.  Hydrogen  and  charcoal,  at  a  red  heat,  reduce 
the  superior  oxides  of  this  metal  to  the  state  of  protoxide, 
without  eliminating  the  pure  metal  at  that  temperature ;  but 


2  MANGANESE. 

at  a  white  heat,  charcoal  deprives  the  metal  of  the  whole  of  its 
oxygen.  The  following  process  is  recommended  by  M.  John 
for  the  reduction  of  manganese  :  it  illustrates  the  chief  points 
to  be  attended  to  in  the  reduction  of  the  less  tractable  metals. 
Instead  of  a  native  oxide,  an  artificial  oxide  of  manganese, 
obtained  by  calcining  the  carbonate  in  a  well-closed  vessel,  is 
operated  upon.  This  oxide,  which  is  preferred  from  being  in 
a  high  state  of  division,  is  mixed  with  oil  and  ignited  in  a 
covered  crucible,  so  as  to  convert  the  oil  into  charcoal.  After 
several  repetitions  of  this  treatment,  the  carbonaceous  mass  is 
reduced  to  powder,  and  made  into  a  firm  paste  by  kneading  it 
with  a  little  oil.  Finally,  this  paste  is  introduced  into  a  cru- 
cible lined  with  charcoal  (creuset  brasque),  the  unoccupied 
portion  of  which  is  filled  up  with  charcoal  powder.  The 
crucible  is  first  heated  merely  to  redness  for  half  an  hour,  to 
dry  the  mass  and  decompose  the  oil ;  after  which  its  cover  is 
carefully  luted  down,  and  it  is  exposed  for  an  hour  and  a  half 
to  the  most  violent  heat  of  a  wind-fiimace  that  the  crucible 
itself  can  support  without  undergoing  fusion.  The  metal  is 
obtained  in  the  form  of  a  serai-globular  mass  or  button  in  the 
lower  part  of  the  crucible,  but  not  quite  pure,  as  it  contains 
traces  of  carbon  and  silicon  derived  from  the  ashes  of  the 
charcoal.  By  igniting  the  metal  a  second  time  in  a  charcoal 
crucible,  with  a  portion  of  borax,  John  obtained  it  more  fusible 
and  brilliant,  and  so  free  from  charcoal  that  it  left  no  black 
powder  when  dissolved  in  an  acid. 

Manganese  is  a  greyish  white  metal,  ha\ing  the  appearance 
of  hard  cast  iron.  Its  density,  according  to  John,  is  801 3; 
while  M.  Berthier  finds  it  to  be  7*05,  and  Bergmann  made  it 
6*850  :  according  to  Hjelm,  it  is  7*0.  From  its  close  resem- 
blance to  iron,  manganese  may  be  expected  to  be  susceptible 
of  magnetism  ;  but  its  magnetic  powers  are  doubtful.  Peclet 
has  endeavoured  to  show  that  manganese  can  assume  and 
preserve  magnetic  polarity  from  the  temperature  —  4°  up  to 
70**,  but  loses  it  again  at  higher  temperatures.     The  small 


OXIDES    OF    MANGANESE.  4 

difference  between  the  atomic  weights  of  iron,  manganese, 
cobalt,  and  nickel,  which  are  respectively  28,  27*67,  29*52,  and 
29*57,  is  remarkable,  attended  as  it  is  by  a  great  analogy 
between  these  metals  in  many  other  respects. 

Manganese  oxidates  readily  in  air,  soon  falling  down  as 
a  black  powder ;  in  water  it  occasions  a  disengagement  of 
hydrogen  gas.  It  is  best  preserved  in  naphtha,  like  potassium, 
or  over  mercury.  Manganese  exhibits  five  degrees  of  oxidation, 
with  two  intermediate  or  compound  oxides. 

OXIDES    OF    MANGANESE. 

Protoxide  or  manganous  oxide     .  MnO. 
Sesquioxide  or  manganic  oxide    .  Mn203. 
Bioxide  or  Peroxide    .         .         .  MnOg. 
Manganoso-manganic   oxide    or 

red  oxide    ....  MuaO^,  or  MnO  +  MugOg. 

Varvicite Mn407,orMn203  +  2Mn02. 

Manganic  acid  ....  MnOg. 
Permanganic  acid      ,         .         .  M^n20>j. 

Protoscide  of  manganese;  Manganous  oxide;  MnO,  35*67 
or  445*9. — This  is  the  oxide  existing  in  the  ordinary  salts  of 
manganese,  which  are  isomorphous  with  the  salts  of  magnesia. 
It  may  be  obtained  by  fusing  at  a  red  heat  in  a  platinum 
crucible,  a  mixture  of  equal  parts  of  pure  chloride  of  man- 
ganese and  carbonate  of  soda,  with  a  small  quantity  of  sal- 
ammoniac.  By  the  reaction  between  the  first-mentioned  salts, 
chloride  of  sodium  is  produced,  together  with  the  carbonate 
of  manganese,  which  is  decomposed  at  a  red  heat,  leaving 
the  protoxide  of  that  metal.  The  hydrogen  of  the  sal-ammo- 
niac at  the  same  time  reduces  to  the  state  of  protoxide  any 
bioxide  which  may  be  formed  by  absorption  of  oxygen  from 
the  air.  Any  one  of  the  superior  oxides  of  manganese,  in  the 
state  of  fine  powder,  may  be  converted  into  protoxide  by 

B    2 


4  MANGANESE. 

passing  hydrogen  gas  over  it,  in  a  porcelain  tube  at  a  red  heat : 
the  bioxide  obtained  by  igniting  the  nitrate  of  the  protoxide 
of  manganese  was  recommended  by  Dr.  Turner  as  the  most 
easily  deoxidated. 

Protoxide  of  manganese  is  a  powder  of  a  greyish  green 
colour,  more  or  less  deep.  When  obtained  by  means  of 
hydrogen  at  a  low  temperature,  it  absorbs  oxygen  from  the 
air,  soon  becoming  brown  throughout  its  whole  mass,  and  is, 
indeed,  sometimes  a  pyrophorus ;  but  when  prepared  by 
hydrogen  at  a  high  temperature,  it  acquires  more  cohesion, 
and  is  permanent. 

Protoxide  of  manganese  dissolves  readily  in  acids,  and  is  a 
strong  base.  Its  salts  are  of  a  pale  rose  tint,  which  is  not 
destroyed  by  sulphurous  or  hydrosulphuric  acid,  and  must  be 
considered  as  a  peculiar  character  of  manganous  salts.  When 
the  solution  is  colourless,  as  it  sometimes  is,  the  fact  is  ex- 
plained, according  to  M.  Gcirgeu,  by  the  presence  of  a  salt 
cf  iron,  nickel,  or  copper ;  the  green  or  blue  tint  of  the  latter 
metals  producing  white  or  a  scarcely  perceptible  violet  shade 
when  combined  with  the  rose  tint  of  a  salt  of  manganese. 
Caustic  alkalies  added  to  solutions  of  manganous  salts  tlirow 
down  the  protoxide  of  manganese  in  the  form  of  a  white 
hydrate,  which  soon  absorbs  oxygen  from  the  air  and  becomes 
brown ;  when  collected  on  a  filter  and  washed,  it  ultimately 
changes  into  a  blackish  brown  powder,  which  is  the  hydrate 
of  the  sesquioxide.  A  similar  change  is  instantaneously 
produced  by  the  action  of  chlorine- water  upon  the  white 
hydrate,  or  by  the  addition  of  chloride  of  lime  to  a  salt  of  the 
protoxide  of  manganese :  but  then  the  hydrated  bioxide  is 
formed.  Protoxide  of  manganese  resembles  magnesia  and 
protoxide  of  iron,  in  being  but  partially  precipitated  by 
ammonia.  The  alkaline  monocarbonates  precipitate  white 
carbonate  of  manganese,  which  does  not  turn  brown  in  the  air, 
and  dissolves  sparingly  in  a  cold  solution  of  sal-ammoniac. 
Bicarbonate  of  potash  precipitates  a  strong  solution  imme- 


OXIDES    OF    MANGANESE.  5 

diately,  and  renders  a  dilute  solution  slightly  turbid ;  but  if 
the  solution  contains  a  free  acid,  so  that  an  excess  of  carbonic 
acid  is  set  free,  no  precipitate  is  formed.  The  earthy  carbon- 
ates do  not  precipitate  manganous  salts.  Hydrosulphuric 
acid  forms  no  precipitate  in  neutral  solutions  of  manganous 
salts  containing  any  of  the  stronger  acids.  In  a  neutral  solution 
of  the  acetate,  a  flesh-coloured  precipitate  is  formed  after  some 
time ;  but  not  if  the  solution  contains  free  acetic  acid.  Sul- 
phide of  ammonium  forms  in  neutral  solutions  of  manganous 
salts  a  flesh-coloured  precipitate  of  hydrated  sulphide  of  man- 
ganese, insoluble  in  excess  of  sulphide  of  ammonium,  but 
readily  soluble  in  acids.  When  exposed  to  the  air,  it  turns 
brown  on  the  surface,  from  oxidation.  The  least  trace  of  iron 
or  cobalt  colours  it  black.  Ferrocyanide  of  potassium  forms 
in  neutral  solutions  of  manganous  salts  a  white  precipitate, 
having  a  tinge  of  red,  and  soluble  in  free  acids.  Ferricyanide 
of  potassium  forms  a  reddish  precipitate,  which  is  insoluble  in 
acids.  Manganous  salts,  and  indeed  all  compounds  of  man- 
ganese, heated  with  borax  or  phosphorus-salt  in  the  outer 
blowpipe  flame,  form  an  amethyst- coloured  bead  containing 
manganoso-manganic  oxide,  which  becomes  colourless  in  the 
inner  flame  by  reduction  of  that  oxide  to  the  protoxide.  This 
character  distinguishes  manganese  from  all  other  metals.  The 
minutest  trace  of  manganese  is  discovered  by  heating  the 
solution  with  a  little  bioxide  of  lead  and  nitric  acid,  when  a 
red  tint  appears  due  to  the  formation  of  permanganic  acid 
(W.  Crum).  An  equally  delicate  reaction  is  obtained  in  the 
dry  way  by  heating  the  substance  supposed  to  contain  man- 
ganese with  carbonate  of  soda  on  platinum  foil  in  the  outer 
blowpipe  flame.  The  smallest  trace  of  manganese  is  indicated 
by  the  formation  of  green  manganate  of  soda.  The  delicacy 
of  the  reaction  may  be  increased  by  adding  a  little  nitre  to  the 
carbonate  of  soda. 

Protosulphide  of  manganese  may  be  procured  in  the  dry 
way,   by   heating   a  mixture  of  bioxide  of  manganese   and 

B  3 


6  MANGANESE. 

sulphur.  Sulphurous  acid  is  disengaged,  and  a  green  powder 
remains,  which  dissolves  in  acids  with  disengagement  of 
hydrosulphuric  acid.  The  same  compound  is  obtained  in  the 
humid  way,  when  acetate  of  manganese  is  decomposed  by 
hydrosulphuric  acid,  or  any  manganous  salt  precipitated  by  an 
alkaline  sulphide.  Protosulphate  of  manganese,  decomposed 
by  hydrogen  at  a  red  heat,  yields  an  oxisulphide.  A  crystal- 
line sulphide  is  obtained  by  passing  the  vapour  of  bisulphide 
of  carbon  over  hydrated  manganic  oxide  ignited  in  a  porcelain 
tube :  the  crystals  are  iron-black  rhombic  prisms,  having  a 
tinge  of  green,  and  yielding  a  dingy  green  powder  ( Volker) . 

Phosphide  of  manganese  is  obtained  by  exposing  an  intimate 
mixture  of  10  parts  of  pure  ignited  bioxideof  manganese,  10 
parts  of  white-burnt  bones,  5  parts  of  white  quartz-sand,  and 
3  parts  of  ignited  lamp-black  for  an  hour  i^  a  closed  Hessian 
crucible  to  a  heat  sufficient  to  melt  cast-iron, — or  by  strongly 
igniting  10  parts  of  ignited  phosphate  of  manganese,  3  parts 
of  ignited  lamp-black,  and  2  parts  of  calcined  borax  in  a  cru- 
cible lined  with  charcoal.  The  product  is  a  very  brittle,  crys- 
talline regulus  of  the  colour  of  grey  cast-iron,  and  of  specific 
gravity  5*951.  It  is  permanent  in  the  air,  glows  when  heated 
in  contact  with  air,  and  bums  with  an  intense  light  when 
heated  with  nitre.  It  appears  to  contain  ^lusP,  and  is  pro- 
bably a  mixture  of  MngP  and  Mn^P,  the  latter  of  which 
compounds  is  left  behind  when  the  substance  is  treated  with 
hydrochloric  acid,  while  the  former  dissolves,  with  evolution 
of  non-spontaneously  inflammable  phosphuretted  hydrogen 
(Wohler). 

Protochloride  of  manganese  :  MnCl  +  4H0  ;  63"  1 7  +  36  or 
789*63  +  450. — This  salt  crystallises  in  thick  tables,  which  are 
oblong  and  quadrilateral,  and  of  a  rose  colour ;  it  is  very 
soluble  in  water,  and  slightly  deliquescent.  The  residuary 
liquid  obtained  in  preparing  chlorine  by  dissolving  bioxide 
of  manganese  in  hydrochloric  acid,  consists  of  chloride  of  man- 
ganese contaminated  with  a  portion  of  sesquichloride  of  iron. 


OXIDES    OF    MANGANESE.  7 

To  remove  the  latter  and  obtain  a  pure  chloride  of  manganese, 
the  solution  should  be  boiled  down  considerably  to  expel  the 
excess  of  acid,  diluted  afterwards  with  water,  and  boiled 
again  with  carbonate  of  manganese,  which  salt  precipitates  the 
whole  of  the  sesquioxide  of  iron,  forming  chloride  of  manganese 
with  its  acid  (Everitt).  If  about  one  fourth  of  the  impure 
solution  of  chloride  of  manganese  be  reserved,  and  precipitated 
by  carbonate  of  soda,  a  quantity  of  carbonate  of  manganese 
will  be  obtained  sufficient  to  precipitate  the  iron  from  the 
other  three-fourths  of  the  liquid,  and  applicable  to  that 
purpose  after  it  has  been  washed.  The  iron  may  likewise  be 
separated  by  evaporating  the  solution  of  the  impure  chloride 
to  dryness,  heating  the  residue  to  low  redness  in  a  crucible,  as 
long  as  hydrochloric  acid  continues  to  escape ;  then  leaving  it 
to  cool,  exhausting  with  boiling  water,  and  filtering.  The 
hydrated  chloride  of  iron  is  resolved  by  the  heat  into  hydro- 
chloric acid  and  sesquioxide,  while  the  chloride  of  manganese 
remains  unaltered,  and  is  easily  dissolved  out  by  water,  all  the 
iron  remaining  behind.  Chloride  of  manganese,  when  free 
from  iron,  is  precipitated  white,  without  any  shade  of  blue,  by 
ferrocyanide  of  potassium.  The  crystals  retain  one  of  their 
four  equivalents  of  water  at  212°  (Brandes),  but  may  be  ren- 
dered anhydrous  at  a  higher  temperature.  Brandes  finds  100 
parts  of  water  to  dissolve  at  50°,  38-3  ;  at  88°,  46-2 ;  at  144-5°, 
55  parts  of  the  anhydrous  salt.  A  higher  temperature,  instead 
of  increasing  the  solubility  of  this  salt,  diminishes  it.  From 
the  aqueous  solution,  chlorine,  with  the  aid  of  heat,  throws 
down  the  black  hydrated  bioxide  of  manganese.  Hypo- 
chlorous  acid  produces  a  similar  result,  with  evolution  of  free 
chlorine.  Absolute  alcohol  dissolves  half  its  weight  of  the 
anhydrous  chloride  of  manganese,  and  afibrds,  by  evaporation 
in  vacuo,  a  crystalline  alcoate,  containing  two  equivalents  of 
alcohol. 

Chloride  of  manganese  forms  two  crystalline  double  salts 
with  chloride  of  ammonium.     One  of  these,  MnCl.  NH^Cl, 

B  4 


8  MANGANESE. 

forms  cubical  crystals,  containing  1  equiv.  water,  according  to 
Rammelsberg,  and  2  eq.  according  to  Hauer.  These  crystals 
when  ignited  leave  manganoso-manganic  oxide  in  microscopic 
pyramids  resembling  Hausmanite.  The  other  salt,  2MnCl. 
NH*C1  +  4H0,  forms  crystals  belonging  to  the  oblique  prismatic 
system  (Hautz) .  Solution  of  chloride  of  manganese  containing 
chloride  of  ammonium,  yields,  on  addition  of  ammonia  and 
exposure  to  the  air,  a  precipitate  of  hydrated  manganoso- 
manganic  oxide  (Otto). 

Protocyanide  of  manganese  is  obtained  in  the  form  of  a  yellow- 
ish or  reddish- white  precipitate,  on  adding  cyanide  of  potassium 
to  the  solution  of  a  manganous  salt.  It  quickly  turns  brown 
on  exposure  to  the  air.  It  is  decomposed  by  the  stronger 
acids,  and  dissolves  in  alkaline  cyanides. 

The  corresponding  fluoride  of  manganese  forms,  vMi  fluoride 
of  silicon,  a  double  salt  which  is  very  soluble  in  water  and 
crystallises  in  long  regular  prisms  of  six  sides.  The  formula 
of  this  double  salt  is,  according  to  Berzelius,  2SiF3  +  3MnF-}- 
21H0. 

Carbonate  of  manganese  is  a  white  insoluble  powder,  which 
acquires  a  brown  tint  when  exposed  in  the  dry  state  at  140°. 
It  is  decomposed  by  a  red  heat.  Carbonate  of  manganese 
occurs  in  the  mineral  kingdom,  in  the  form  of  manganese-spar y 
but  never  in  a  state  of  purity,  being  mixed  with  the  carbonates 
of  lime  and  iron,  which  have  the  same  crystalline  form,  viz.  the 
rhombohedral.  Its  presence  in  spathic  carbonate  of  iron  is 
said  to  be  the  cause  why  the  latter  yields  an  iron  peculiarly 
adapted  for  the  manufacture  of  steel. 

Protosulphate  of  manganese ;  Manganous  sulphate ;  MnO, 
SO3  +  7HO. — A  solution  of  this  salt,  used  in  dyeing  and  en- 
tirely free  from  iron,  is  prepared  by  igniting  bioxide  of  man- 
ganese mixed  with  about  one-tenth  of  its  weight  of  pounded 
coal  in  a  gas  retort.  The  protoxide  thus  formed  is  dissolved  in 
sulphmic  acid,  with  the  addition  of  a  little  hydrochloric  acid 
towards  the  end  of  the  process ;  the  sulphate  is  evaporated  to 


OXIDES    OF    MANGANESE.  9 

dryness,  and  again  heated  to  redness  in  the  gas  retort.  The  iron 
is  found  after  ignition  in  the  state  of  sesquioxide  and  insoluble, 
the  persulphate  of  iron  being  decomposed,  while  the  sulphate 
of  manganese  is  not  injured  by  the  temperature  of  ignition, 
and  remains  soluble.  The  salt  may  also  be  obtained  by  heating 
bioxide  of  manganese,  previously  freed  from  the  carbonates 
of  lime  and  magnesia  by  boiling  with  dilute  sulphuric  acid, 
with  an  equal  weight  of  strong  oil  of  vitriol,  and  gently  ignit- 
ing  the  resulting  mass  for  an  hour,  to  decompose  the  sulphates 
of  iron  and  copper  formed  at  the  same  time.  The  manganous 
sulphate,  which  remains  unaltered,  is  then  dissolved  in  water, 
and  the  solution  evaporated  to  the  crystallising  point.  The 
solution  is  of  an  amethystine  colour,  and  does  not  crystallise 
readily.  When  cloth  is  passed  through  sulphate  of  manganese 
and  afterwards  through  a  caustic  alkali,  protoxide  of  manganese 
is  precipitated  upon  it,  and  rapidly  becomes  brown  in  the  air ; 
or  it  is  peroxidised  at  once  by  passing  the  cloth  through  a 
solution  of  chloride  of  lime.  The  colour  thus  produced  is 
called  manganese-brown. 

Crystallised  undei  42°,  the  sulphate  of  manganese  gives 
crystals  containing  7 HO,  which  have  the  same  form  as  sul- 
phate of  iron.  The  crystals  wbich  form  between  45°  and  68°, 
contain  5 HO,  and  are  isomorphous  with  sulphate  of  copper. 
By  a  higher  temperature,  from  68°  to  86°,  a  third  set  of  crystals 
is  obtained,  which  contain  4H0  :  their  form  is  a  right  rhombic 
prism.  The  sulphate  of  iron  and  other  sulphates  also  assume 
the  same  form  (Mitscherlich) .  This  salt  loses  3H0  at  243°, 
but  retains  1  eq.  even  at  400°,  like  the  other  magnesian  sul- 
phates. M.  Kuhn  finds,  that  when  a  strong  solution  of  the 
sulphate  of  manganese  is  mixed  with  sulphuric  acid  and  evapo- 
rated by  heat,  a  granular  salt  is  precipitated,  which  contains 
only  one  equivalent  of  water.  This  sulphate  also  forms 
with  sulphate  of  potash  a  double  salt  containing  6H0.  The 
anhydrous  salt  is  soluble,  according  to  Brandes,  in  2  parts  of 
water  at  59°,  in  1  part  at  122° ;  but  above  the  latter  tempera- 


10  MANGANESE. 

ture,  the  salt  becomes  less  soluble.  The  tetra-hydrated  salt 
dissolves  in  0*883  part  of  water  at  43'3°  ;  in  079  part  at  50°; 
in  0-82  part  at  65-8° ;  in  0-67  part  at  99*5°  ;  and  in  1-079  part 
at  2'1°.  Manganous  sulphate  is  insoluble  in  absolute  alcohol, 
but  dissolves  in  500  parts  of  spirit  of  the  strength  of  55 
per  cent. 

Hyposulphate  of  manganese ;  MnO  .  S205-f6HO.  For  the 
preparation,  see  I.  335. — The  bioxide  of  manganese  used  in 
preparing  it  should  be  previously  treated  with  nitric  acid,  to 
dissolve  out  the  hydrated  oxide,  and  be  well  washed.  The  salt 
forms  rose-coloured,  generally  indistinct,  crystals,  belonging 
to  the  doubly  oblique  prismatic  system  (Marignac).  The 
oxalate  of  manganese  is  a  highly  insoluble  salt.  The  acetate 
is  soluble  in  3^  parts  of  cold  water,  and  also  in  alcohol.  Bitar- 
trate  of  potash  dissolves  protoxide  of  manganese,  and  foiTns  a 
very  soluble  double  salt,  the  tartrate  of  potash  and  manganese j 
which  can  be  obtained,  although  with  difficulty,  in  regular 
crystals. 

Sesquioxide  of  manganese;  Manganic  oxide;  MujOg;  79'34 
or  991 '8. — This  oxide  is  left  of  a  dark  brown,  almost  black 
colour,  when  the  nitrate  of  the  protoxide  is  gently  ignited. 
It  also  occurs  crystallised  in  the  mineral  kingdom,  although 
rarely;  its  density  is  4*818,  and  it  is  named  hraunite  as  a 
mineral  species.  The  hydrate  of  manganic  oxide  is  formed 
by  the  oxidation  in  air  of  manganous  hydrate.  Manganic 
hydrate  also  frequently  occurs  in  nature  of  a  black  colour,  both 
crystallised  and  amorphous,  and  is  often  mixed  with  the  bi- 
oxide of  manganese.  It  constitutes  the  mineral  species  man- 
ganite,  of  which  the  density  is  4*3  to  4*4,  and  the  formula 
Mn203,  HO.  This  hydrate  may  be  artificially  prepared  by 
heating  finely  divided  bioxide  of  manganese  with  monohy- 
drated  sulphuric  acid,  decomposing  the  resulting  manganic 
sulphate  with  water,  and  washing  it  thoroughly  (Carius).  This 
oxide  colours  glass  of  a  red  or  violet  tint.     The  common  violet 


OXIDES    OF    MANGANESE.  11 

or  purple  stained  glass  contains  manganic  oxide;  also  the 
amethyst. 

Manganic  oxide  is  a  base  isomorphous  with  alumina  and 
sesquioxide  of  iron.  It  dissolves  in  cold  hydrochloric  acid 
without  decomposition.  Concentrated  sulphuric  acid  combines 
with  it  at  a  temperature  a  little  above  212°,  but  does  not  form 
a  solution.  Dilute  sulphuric  acid  does  not  dissolve  it,  either 
in  the  cold  or  when  gently  heated,  unless  manganous  oxide  is 
present,  even  in  very  small  quantities,  in  which  case  a  violet 
solution  is  formed;  hence  the  commonly  received  statement  that 
manganic  oxide  forms  a  red  solution  with  sulphuric  acid 
(Carius).  At  somewhat  elevated  temperatures,  acids  reduce 
the  sesquioxide  of  manganese  to  protoxide,  with  evolution  of 
oxygen. 

Manganic  sulphate ;  MngOg  .  3  SO3, — Prepared  by  mixing 
finely  divided  bioxide  of  manganese  (obtained  by  passing 
chlorine  gas  through  a  solution  of  carbonate  of  soda  in  which 
carbonate  of  manganese  is  suspended)  with  monohydrated 
sulphuric  acid  to  the  consistence  of  a  pulp,  and  gradually 
heating  the  mixture  in  an  oil-bath  to  about  276°,  at  which 
point  the  mass  becomes  dark  green  and  more  mobile.  It  is 
then  drained  on  a  plate  of  pumice-stone  to  remove  the  greater 
part  of  the  sulphuric  acid  ;  afterwards  stirred  up  in  a  warm 
basin  with  the  strongest  nitric  acid  (free  from  nitrous  acid) ; 
again  drained  on  pumice-stone ;  and  this  treatment  repeated 
several  times  :  lastly,  it  is  dried  in  the  oil-bath  at  266°,  and 
preserved  in  carefully  dried  tubes. — Manganic  sulphate  thus 
obtained  is  a  dark  green  powder  which  exhibits  no  traces  of 
crystallisation.  It  may  be  heated  to  320°  without  decompo- 
sition, but  at  higher  temperatures  gives  off  oxygen  and  is 
reduced  to  manganous  sulphate.  At  ordinary  temperatures 
it  is  all  but  insoluble  in  concentrated  sulphuric  and  nitric 
acid ;  with  the  former  it  may  be  heated  nearly  to  the  boil- 
ing point  without  alteration,  but,  when  boiled  with  the  acid, 
it  dissolves  as  manganous  sulphate,  with  evolution  of  oxygen. 


11^  MANGANESE. 

Heated  with  concentrated  nitric  acid  to  212°,  it  turns  brown, 
but  resumes  its  green  colour  when  the  acid  is  evaporated  at  the 
lowest  possible  temperature.  In  strong  hydrochloric  acid,  it 
dissolves,  like  the  pure  sesquioxide,  forming  a  brown  solution, 
which  when  heated  gives  off  chlorine  till  all  the  sesquioxide  of 
manganese  is  reduced  to  protoxide.  Organic  substances,  heated 
with  the  dry  salt,  decompose  it  with  considerable  violence. 
The  salt  absorbs  moisture  very  rapidly,  so  that  it  must  always 
be  kept  in  sealed  tubes.  Small  quantities  of  it  deliquesce  in 
a  few  seconds,  forming  a  violet  solution, which,  however,  soon 
becomes  brown  and  turbid  from  separation  of  the  hydrated 
oxide.  Water  decomposes  the  salt  rapidly,  especially  when 
heated,  separating  the  pure  hydrated  sesquioxide.  Hence 
the  mode  of  preparing  the  hydrate  above  mentioned.  Sul- 
phuric acid,  somewhat  diluted,  decomposes  manganic  sulphate, 
converting  it  into  a  red-brown  powder,  which  appears  to  be  a 
basic  salt.*  Manganic  sulphate  forms  an  alum  with  sulphate 
of  potash  (Mitscherlich)  :  this  salt  occurs  native  in  needle- 
shaped  crystals  at  Alum  Point,  on  the  Great  Salt  Lake  in 
North  America  (L.  D.  Gale). 

Sesquichloride  of  manganese  (MujClg)  is  formed  when  the 
sesquioxide  is  dissolved  in  hydrochloric  acid  at  a  low  tempera- 
ture. The  solution  is  yellowish  brown  or  black,  according  to 
its  degree  of  concentration,  and  is  decomposed  by  a  slight 
elevation  of  temperature,  with  evolution  of  chlorine.  A  cor- 
responding sesquifluoride  may  be  crystallised. 

Sesquicyanide  of  manganese. — A  compound  of  tliis  cyanide 
is  formed,  when  manganous  acetate  is  mixed  with  hydrocyanic 
acid  in  excess,  then  neutralised  with  potash  and  evaporated. 
The  manganous  cyanide  then  absorbs  oxygen,  and  is  converted 
into  hydrated  manganic  oxide  and  manganic  cyanide,  which  last 
combines  with  cyanide  of  potassium,  and  appears,  on  the  cooling 
of  a  concentrated  solution,  in  red  crystals,  which  dissolve  easily 

♦  Carius,  Jnn.  Ch.  Pharm.  xcviii.,  53. 


OXIDES    OP    MANGANESE.  13 

in  water  (Mitscherlich) .  This  salt  is  analogous  to  red  prus- 
siate  of  potash^  containing  manganese  instead  of  iron,  and  may, 
therefore,  be  represented  as  containing  manganicyanogen — a 
manganicyanide  of  potassium,  K3(Mn2Cy6).  As  a  double 
cyanide,  its  formula  would  be,  SKCy-MugCyg. 

Red  oxide  of  manganese,  MnCMugjOg,  named  by  Berzelius 
manganoso-manganic  oxide,  is  always  produced  when  any  oxide 
of  manganese  is  heated  strongly  in  air.  It  is  a  double 
oxide,  being  a  compound  of  single  equivalents  of  protoxide  and 
bioxide  of  manganese.  It  forms  the  mineral  Hausmanite, 
which  differs  from  manganite  in  having  manganous  oxide  in 
place  of  water.  Its  density  is  4i-722.  Berthier  finds  that 
strong  nitric  acid  dissolves  out  the  protoxide  of  manganese 
from  the  red  oxide,  and  leaves  a  remarkable  hydrate  of  the 
bioxide,  of  which  the  formula  is  4Mn02  +  HO. 

Bioxide  or  Peroxide  of  manganese;  Black  oxide  of  manga- 
nese ;  MnOg ;  4367  or  545-9. — This  is  the  well-known  ore  of 
manganese  employed  in  the  preparation  of  oxygen  and  chlorine. 
It  generally  occurs  massive,  of  an  earthy  appearance,  and  con- 
taminated with  various  substances,  such  as  sesquioxide  of  iron, 
silica,  and  carbonate  of  lime ;  but  sometimes  of  a  fibrous  tex- 
ture, consisting  of  small  prisms  radiating  from  a  common 
centre.  Its  density  varies  from  4-819  to  494;  as  a  mineral 
species  it  has  been  named  pyrolusite."^  Another  important 
variety  of  this  ore,  known  as  wad,  is  essentially  a  hydrate, 
containing,  according  to  Dr.  Turner,  1  eq.  of  water  to  2  eq.  of 
peroxide.  A  hydrated  bioxide,  consisting  of  single  equivalents 
of  its  constituents,  is  formed  by  precipitating  the  protosalts  of 
manganese  with  chloride  of  lime ;  and  the  same  compound 
results  from  the  decomposition  of  the  acids  of  manganese,  when 
diluted  with  water  or  an  acid.  It  is  possible  that  the  equiva- 
lent of  this  oxide  should  be  doubled,   and  that   its   proper 


*  From  irvp,  fire,  and  A.u«,  I  wash  ;  in  allusion  to  its  being  employed  to 
discharge  the  brown  and  green  tints  of  glass. 


14  MANGANESE. 

formula  is  Mn204,  corresponding  with  peroxide  of  chlorine^ 
CIO4. 

Bioxide  of  manganese  loses  one-fourth  of  its  oxygen  at  a 
low  red  heat,  and  is  changed  into  sesquioxide ;  at  a  bright  red 
heat  it  loses  more  oxygen,  and  becomes  red  oxide,  the  condition 
into  which  all  the  oxides  of  manganese  pass  when  ignited  strongly 
in  the  open  air.  The  bioxide  does  not  unite  either  with 
acids  or  with  alkalies.  When  boiled  with  sulphuric  acid,  it  yields 
oxygen  gas  and  a  sulphate  of  the  protoxide.  In  hydrochloric 
acid  it  dissolves  with  gentle  digestion,  evolving  chlorine  gas, 
and  forming  protochloride  of  manganese  (page  6).  It  is  exten- 
sively used  in  the  arts  for  preparing  chlorine,  and  also  to 
preserve  glass  colourless  by  its  oxidating  action.  In  the  last 
application,  it  is  added  to  the  vitreous  materials  in  a  relatively 
small  proportion,  and  becomes  protoxide,  which  is  not  a  colour- 
ing oxide,  while  as  sesquioxide  it  would  stain  glass  purple. 
At  the  same  time  it  destroys  carbonaceous  matter,  and  converts 
protoxide  of  iron,  which  colours  glass  green,  into  sesquioxide, 
which  is  less  injurious. 

The  mineral  varvicite  was  discovered  by  Mr.  R.  Phillips 
among  some  ores  of  manganese  from  Hartshill  in  Wanvick- 
shire.  It  is  distinguished  from  the  bioxide  by  being  much 
harder,  having  more  of  a  lamellated  structure,  and  by  yielding 
water  freely  when  heated  to  redness.  Its  density  is  4*531. 
It  may  be  supposed  to  consist  of  1  eq.  of  sesquioxide,  and  2 
eq.  of  bioxide  with  1  eq.  of  water  (Dr.  Turner) ;  its  formula 
is,  therefore,  MuaOg  .  MuaO^  +  HO. 


VALUATION    OF    BIOXIDE    OF    MANGANESE. 

The  numerous  applications  of  the  higher  oxides  of  manganese 
depending  upon  the  oxygen  which  they  can  furnish,  render 
it  important  to  have  the  means  of  easily  and  expeditiously 
estimating  their  value  for  such  purposes.  The  value  of 
these  oxides  is  exactly  proportional  to  the  quantity  of  chlorine 


VALUATION    OF    BIOXIDE    OF    MANGANESE.  15 

wliich  they  produce  when  dissolved  in  hydrochloric  acid^  and 
the  chlorine  can  be  estimated  by  the  quantity  of  protosulphate 
of  iron  which  it  oxidises.  Of  pure  bioxide  of  manganese 
43'7  parts  (1  eq.)  produce  35'5  parts  of  chlorine,  which  oxi- 
dise 278  parts  (2  eq.)  of  crystallised  protosulphate  of  iron. 
Hence  50  grains  of  bioxide  of  manganese  yield  chlorine  suffi- 
cient to  oxidise  317  grains  (more  exactly,  316*5  grs.)  of  proto- 
sulphate of  iron. 

50  grains  of  the  powdered  oxide  of  manganese  to  be 
examined  are  weighed  out,  and  also  any  known  quantity,  not 
less  than  317  grains,  of  the  sulphate  of  iron  (copperas)  em- 
ployed in  chlorimetry.  The  oxide  of  manganese  is  thrown 
into  a  flask  containing  an  ounce  and  a  half  of  strong  hydrochloric 
acid,  diluted  with  half  an  ounce  of  water,  and  a  gentle  heat 
applied.  The  sulphate  of  iron  is  gradually  added  in  small 
quantities  to  the  acid,  so  as  to  absorb  the  chlorine  as  it  is 
evolved ;  and  the  addition  of  that  salt  continued,  till  the  liquid, 
after  being  heated,  gives  a  blue  precipitate  with  the  red  prussiate 
of  potash,  and  has  no  smell  of  chlorine,  which  are  indications 
that  the  protosulphate  of  iron  is  present  in  excess.  By 
weighing  what  remains  of  the  sulphate  of  iron,  the  quantity 
added  is  ascertained ;  say  m  grains.  If  the  whole  manganese 
were  bioxide,  it  would  require  317  grains  of  sulphate  of  iron, 
and  that  quantity  would,  therefore,  indicate  100  per  cent,  of 
bioxide  in  the  specimen ;  but  if  a  portion  of  the  manganese 
only  is  bioxide,  it  will  consume  a  proportionally  smaller 
quantity  of  the  sulphate,  which  quantity  will  give  the  propor- 
tion of  the  bioxide,  by  the  proportion:  as  317  :  100  : :  ?/n 
per-centage  required.  The  per-centage  of  bioxide  of  man- 
ganese is  thus  obtained  by  multiplying  the  number  of  grains 
of  sulphate  of  iron  oxidised  by  0*317.  It  also  follows  that 
the  per-centage  of  chlorine  which  the  same  specimen  of  man- 
ganese would  afford,  is  obtained  by  multiplying  the  number 
of  grains  of  sulphate  of  iron  oxidised  by  0*2588. 

Another  mode  of  estimation  is  to  pass  the  chlorine  gas. 


16  MANGANESE. 

obtained  by  heating  the  manganese  in  a  flask  with  liydro- 
chloric  acid,  into  a  solution  of  sulphurous  acid,  quite  free 
from  sulphuric  (it  should  give  no  precipitate  with  chloride  of 
barium) ;  the  chlorine  converts  an  equivalent  quantity  of 
sulphurous  acid  into  sulphuric.  The  liquid  is  then  mixed 
with  chloride  of  barium,  and  boiled  to  expel  the  excess  of  sul- 
phurous acid,  after  which  the  sulphate  of  baryta  is  thrown  on 
a  filter,  washed,  dried,  ignited,  and  weighed.  The  11 6' 64  gr., 
or  1  eq.  of  sulphate  of  baryta,  correspond  to  43*7  gr.,  or  1  eq. 
of  bioxide  of  manganese. 

The  value  of  commercial  oxide  of  manganese  may  also  be 
estimated  by  heating  it  with  hydrochloric  acid  and  oxalic  acid. 
The  disengaged  chlorine  then  converts  the  oxalic  acid  into 
carbonic  acid, —  2  eq.  of  carbonic  acid  representing  1  eq.  of 
chlorine,  and  therefore  1  eq.  of  bioxide  of  manganese  : 

C2HO4  +  CI  =  2CO2  +  HCl. 

A  convenient  apparatus  for  the  determination  is  a  small 
J,-    ^  light  glass  flask  (fig.   1),  of  3  or  4  oz. 

capacity,  having  a  lipped  edge,  and 
fitted  with  a  perforated  cork.  A  piece 
of  tube,  about  3  inches  long,  drawn 
out  at  one  end,  and  filled  with  frag- 
ments of  chloride  of  calcium,  to  absorb 
water,  is  fitted  by  means  of  a  small 
cork  and  a  bent  tube  to  the  mouth  of 
the  flask.  A  short  tube  closed  at  one 
end,  and  small  enough  to  go  into  the  flask,  is  used  to 
contain  the  hydrochloric  acid.  Fifty  grains  of  the  mineral, 
in  the  state  of  very  fine  powder,  are  introduced  into  the 
flask,  together  with  about  half  an  ounce  of  cold  water,  and 
100  grains  of  strong  hydrochloric  acid  in  the  tube,  as  shown 
in  the  figure :  50  grains  of  crystallised  oxalic  acid  are  then 
added,  the  chloride  of  calcium  tube  fitted  on,  and  the  whole 
quickly  weighed.     The  flask  is  then  tilted  so  as  to  allow  the 


VALUATION    OF   BIOXIDE    OP   MANGANESE.  17 

hydrocUoric  acid  to  flow  out  of  the  tube,  and  come  in 
contact  with  the  mixture  of  manganese  and  oxalic  acid,  and 
a  gentle  heat  applied  to  determine  the  action.  Carbonic  acid 
is  then  evolved,  and  escapes  through  the  chloride  of  calcium 
tube.  To  expel  the  last  portions  of  carbonic  acid,  the  liquid 
must  be  ultimately  heated  till  it  boils ;  after  which  it  is  left 
to  cool,  and  weighed :  the  loss  of  weight  gives  the  quantity 
of  carbonic  acid.  Now,  as  43*67,  the  equivalent  of  bioxide 
of  manganese,  is  nearly  double  that  of  carbonic  acid,  which 
is  22,  the  loss  of  weight  in  the  apparatus  may  be  taken  to 
represent  the  quantity  of  real  bioxide  in  the  50  grains  of 
the  sample.     [For  other  methods,  see  Appendix.] 

To  obtain  a  complete  appreciation  of  the  value  of  a  sample 
of  manganese,  it  is  not  sufiicient  to  know  the  per-centage  of 
real  bioxide  in  it,  —  or,  which  comes  to  the  same  thing,  the 
quantity  of  chlorine  it  is  capable  of  yielding,  —  but  we  must 
also  know  the  quantity  of  hydrochloric  acid  which  must  be 
consumed  for  evolving  this  chlorine.  If  the  sample  consists 
of  pure  bioxide,  half  the  acid  used  will  give  up  its  chlorine ; 
if  it  be  pure  sesquioxide,  only  a  third  of  the  acid  wiU  be 
changed  into  chlorine.  The  quantity  of  acid  required  will 
therefore  be  greater  in  the  latter  case  than  in  the  former  in 
the  ratio  of  3  :  2.  Lastly,  if  the  oxide  contains  lime,  baryta, 
or  oxide  of  iron,  these  bases  will  neutralise  a  portion  of  the 
acid  without  supplying  any  chlorine.  To  determine  the  ex- 
penditure of  acid,  a  known  weight  of  the  oxide  is  heated  with 
a  known  quantity  of  hydrochloric  acid  of  given  strength,  the 
chlorine  being  sufiered  to  escape,  but  the  hydrochloric  acid 
which  would  otherwise  escape  undecomposed  being  collected 
in  a  small  receiver  moistened  on  the  inside.  When  the  action 
is  over,  the  acid  thus  condensed  is  added  to  that  in  the  flask, 
the  whole  diluted  with  water,  and  the  quantity  of  free  acid 
determined  by  adding  a  graduated  alkaUne  solution,  till  the 
precipitate  which  forms  no  longer  redissolves  on  agitation. 
The  quantity  of  free  acid  thus  determined  is  then  to  be  de« 

VOL.  II.  c 


18  MANGANESE. 

ducted  from  the  original  quantity,  and  the  difference  gives  the 
quantity  consumed. 

Manganic  add;  MnOgj  51*67  or  645*9. — When  bioxide 
of  manganese  is  strongly  ignited  with  hydrate  or  carbonate  of 
potash  in  excess,  manganic  acid  is  formed,  under  the  influence 
of  the  alkali,  together  with  a  lower  oxide  of  manganese. 
Ignition  in  open  vessels,  or  with  an  admixture  of  nitrate  of 
potash,  increases  the  production  of  the  acid,  by  the  absorption 
of  oxygen  which  then  occurs.  The  product  has  long  been 
known  as  mineral  chameleon^  from  the  property  of  its  solu- 
tion, which  is  green  at  first,  to  pass  rapidly  through  several 
shades  of  colour.  But  a  more  convenient  process  for  pre- 
paring manganate  of  potash  is  that  recommended  by  Dr. 
Gregory.  He  mixes  intimately  4  parts  of  bioxide  of  man- 
ganese in  fine  powder  with  3  J  parts  of  chlorate  of  potash,  and 
adds  them  to  5  parts  of  hydrate  of  potash  dissolved  in  a  small 
quantity  of  water.  The  mixture  is  evaporated  to  dryness, 
powdered,  and  afterwards  ignited  in  a  platinum  crucible,  but 
not  fused,  at  a  low  red  heat.  The  ignited  mass,  digested  in  a 
small  quantity  of  cold  water,  forms  a  deep  green  solution  of 
the  alkaline  manganate,  which  may  be  obtained  in  crystals  of 
the  same  colour  by  evaporating  the  solution  over  sulphuric 
acid  in  the  air-pump.  Zwenger,  by  igniting  bioxide  of  man- 
ganese with  3  parts  of  nitric  acid,  and  evaporating  the  aqueous 
solution  in  vacuo,  obtained  reddish-brown  crystals  containing 
KO.MnOg.  On  exposure  to  the  air,  they  became  dull  and 
dark  green.  The  manganates  were  discovered  by  Mitscher- 
lich  to  be  isomorphous  with  the  sulphates  and  clu*omates.  It 
has  not  yet  been  found  possible  to  isolate  manganic  acid.  Its 
salts  in  solution  readily  undergo  decomposition,  unless  an 
excess  of  alkali  is  present ;  and  are  also  destroyed  by  contact 
of  organic  matter,  such  as  paper. 

Permanganic  acid,  Mn207;  111*34  or  1391*8. — When  the 
green  solution  of  manganate  of  potash,  prepared  as  above 
directed,  is  diluted  with  boiling  water,  hydrated  bioxide  of 


VALUATION    OF    BIOXIDE    OP    MANGANESE.  19 

manganese  subsides,  and  the  liquid  assumes  a  beautiful  pink 
or  violet  colour.  The  manganic  acid  is  resolved  into  bioxide 
of  manganese  and  hypermanganic  acid : 

SMnOg  =  MnOg  +  Mn^O^, 

The  permanganate  of  potash  should  be  rapidly  concentrated, 
without  contact  of  organic  matter,  and  allowed  to  crystallize. 
A  better  process  for  obtaining  this  salt  is  to  mix  1  part  of 
bioxide  of  manganese,  in  very  fine  powder,  with  1  part  of 
chlorate  of  potash ;  introduce  this  mixture  into  a  solution  of 
IJ-  part  of  caustic  potash  in  the  smallest  possible  quantity 
of  water ;  evaporate  to  dryness,  during  which  process  a  con- 
siderable quantity  of  manganate  of  potash  is  formed ;  then 
heat  the  mixture  slowly  to  dull  redness ;  boil  the  product  in 
water;  filter  through  asbestos,  and  concentrate  by  evapora- 
tion :  the  liquid,  on  cooling,  deposits  permanganate  of  potash 
in  crystals.  It  may  be  purified  by  solution  in  a  small  quan- 
tity of  boiling  water,  and  recrystallisation.  The  crystals  are 
of  a  dark  purple  colour,  almost  black,  and  soluble  in  sixteen 
times  their  weight  of  cold  water ;  they  were  found  by  Mitscher- 
lich  to  be  isomorphous  with  perchlorate  of  potash ;  they  dis- 
solve in  16  parts  of  water  at  60°  (Regnault).  The  perman- 
ganates give  out  oxygen  when  heated,  and  are  reconverted 
into  manganates.  Their  solutions  have  a  rich  purple  colour, 
and  are  so  stable  that  they  may  be  boiled,  if  concentrated. 
A  small  portion  of  a  permanganate  imparts  a  purple  colour  to 
a  very  large  quantity  of  water. 

When  a  strong  solution  of  caustic  potash  is  added  to  a 
dilute  solution  of  permanganate  of  potash,  the  liquid  changes 
colour,  assuming  first  a  violet,  and  afterwards  an  emerald- 
green  tint.  The  permanganate  is  in  fact  converted  into 
manganate,  a  double  quantity  of  potash  having  entered  into 
combination  with  the  acid  : 

KO.MnaOy  +  KO  =  2(KO.Mn03)  +  O. 

c  2 


20  MANGANESE. 

The  oxygen  thus  liberated  remains  dissolved  in  the  water. 
This  transformation  is  due  to  the  great  basic  power  of  the 
potash.  Acids  produce  the  contrary  effect,  that  is  to  say, 
they  convert  manganates  into  permanganates. 

The  insoluble  manganate  of  baryta  may  be  formed  by 
fusing  bioxide  of  manganese  with  nitrate  of  baryta;  and 
when  mixed  with  a  little  water,  and  decomposed  by  an  equi- 
valent quantity  of  sulphuric  acid,  affords  free  permanganic 
acid.  In  Mitscherlich's  experiments,  the  free  acid  appeared 
to  be  a  body  not  more  stable  than  bioxide  of  hydrogen, 
being  decomposed  between  86**  and  104®,  with  escape  of 
oxygen  gas  and  precipitation  of  hydrated  bioxide  of  man- 
ganese. It  bleached  powerfully,  and  was  rapidly  destroyed 
by  all  kinds  of  organic  matter.  M.  Hunefeld,  on  the  other 
hand,  obtained  permanganic  acid  in  a  state  in  which  it  could 
be  preserved,  evaporated,  redissolved,  &c.  He  washed  the 
manganate  of  baryta  with  hot  water,  by  which  it  is  resolved 
into  bioxide  of  manganese  and  permanganate  of  baryta,  and 
then  added  to  it  the  quantity  of  phosphoric  acid  exactly 
necessary  to  neutralise  the  baryta.  The  liberated  perman- 
ganic acid  was  dissolved  out,  evaporated  to  dryness,  and  by  a 
second  solution  and  evaporation,  obtained  in  the  form  of  a 
reddish-brown  mass,  crystalline  and  radiated,  which  exhibited 
the  lustre  of  indigo  at  some  points  and  was  entirely  soluble 
in  water.  When  dry  permanganic  acid  was  fused  in  a  retort 
with  anhydrous  sulphuric  acid,  and  afterwards  distilled  at  a 
higher  temperature,  an  acicular  sublimate  of  a  crimson  red 
colour  was  obtained,  which  appeared  to  be  a  combination  of 
permanganic  and  sulphuric  acids.  (Berzelius^s  Traite,  i.  522.) 
When  monohydrated  sulphuric  acid  is  poured  upon  a  some- 
what considerable  quantity  of  crystallised  permanganate  of 
potash,  the  salt  is  decomposed  with  great  evolution  of  heat, 
red  flames  bursting  out,  oxygen  being  evolved,  and  manganic 
oxide  set  free  in  dark-brown  flakes  and  shreds  like  spider- 
lines.     The  red  flames  seem  to  show  that  permanganic  acid 


ISOMORPHOUS    RELATIONS    OF    MANGANESE.  21. 

is  gaseous  at  the  high  temperature  produced  by  the  reaction* 
(Wohler.) 

Perchloride  of  manganese^  Mn2Cl7,  is  a  greenish  yellow 
gas,  which  condenses  at  (f  F.  into  a  liquid  of  a  greenish- 
brown  colour.  This  liquid  diffuses  purple  fumes,  owing  to 
the  formation  of  hydrochloric  and  permanganic  acids,  by  the 
decomposition  of  the  moisture  of  the  air.  It  was  formed  by 
Dumas  by  dissolving  manganate  of  potash  in  oil  of  vitriol, 
pouring  the  solution  into  a  tubulated  retort,  and  addiug  by 
degrees  small  portions  of  chloride  of  sodium  or  potassium, 
completely  freed  from  water  by  fusion.  The  perchloride  of 
manganese  is  the  result  of  a  reaction  between  the  liberated 
hypermanganic  and  hydrochloric  acids  : 

MngOy  +  7HCl=Mn2Cl7  +  7H0. 

A  corresponding  perfluoride  of  manganese  was  formed  by 
Wohler  by  distilling,  in  a  platinum  retort,  a  mixture  of 
manganate  of  potash  and  fluor-spar  in  powder,  with  fuming 
sulphuric  acid.  It  is  a  greenish-yeUow  gas,  which  likewise 
produces  purple  fumes  in  damp  air. 

Isomorphous  relations  of  manganese.  —  There  is  no  other 
element  whose  compounds  enter  into  so  many  isomorphous 
groups,  and  connect  so  large  a  proportion  of  the  elements  by 
the  tie  of  isomorphism,  as  manganese.  The  salts  of  its  prot- 
oxide are  strictly  isomorphous  with  the  salts  of  magnesia  and 
its  class ;  so  that  manganese  belongs  to  and  represents  the 
magnesian  famUy  of  elements.  The  same  metal  connects 
the  sulphur  family  with  the  magnesian,  by  the  isomorphism 
of  the  sulphates  and  manganates ;  and,  therefore,  sulphur,  se- 
lenium, and  tellurium  are  thus  allied  to  the  magnesian  metals. 
An  equally  interesting  relation  is  that  of  permanganic  with 
perchloric  acid,  and  the  isomorphism,  which  it  establishes,  of 
2  equivalents  of  manganese  with  1  equivalent  of  chlorine, 
and  the  other  members  of  its  family. 

c  3 


22  MANOANESE. 


ESTIMATION    OP    MANGANESE,  AND    METHODS    OF    SEPARATING  IT 
FROM    THE    PRECEDING    METALS. 

The  usual  method  of  precipitating  manganese  from  the  so- 
lution of  a  manganous  salt,  is  to  add  carbonate  of  soda  at  a 
boiling  heat.  The  precipitated  carbonate  of  manganese  is 
then  well  washed  with  boiling  water,  and  calcined  at  a  strong 
red  heat,  whereby  it  is  converted  into  manganoso-manganic 
oxide,  Mn304,  containing  72*11  per  cent,  of  manganese.  If 
the  solution  contains  a  considerable  quantity  of  ammoniacal 
salts,  it  must  be  evaporated  after  mixing  it  with  excess  of 
carbonate  of  soda,  and  the  soluble  salts  dissolved  out  of  the 
residue  by  water. 

Manganese  is  separated  from  the  alkali-metals  by  means  of 
carbonate  of  soda  or  sulphide  of  ammonium,  which  latter 
precipitates  it  in  the  form  of  sulphide.  The  sulphide  is 
washed  with  water  containing  a  small  quantity  of  sulphide  of 
ammonium ;  then  redissolved  in  acid ;  and  the  manganese 
precipitated  from  the  solution  by  carbonate  of  soda. 

From  barium  and  strontium,  manganese  is  easily  separated 
by  means  of  sulphate  of  soda,  which  throwsdown  the  barytaand 
strontia  as  sulphates ;  also  by  sulphide  of  ammonium.  From 
lime  and  manganese  it  is  separated  by  sulphide  of  ammonium, 
which,  if  the  solution  be  sufficiently  dilute,  precipitates  the 
manganese  alone  in  the  form  of  sulphide.  The  separation 
from  lime  may  also  be  effected  by  means  of  oxalate  of  ammo- 
nia, after  the  addition  of  chloride  of  ammonium  to  keep  the 
manganese  in  solution. 

From  alumiQa  and  glucina,  manganese,  if  in  small  or  mode- 
rate quantity  only,  may  be  separated  by  boiling  the  solution 
with  potash  in  an  open  vessel.  The  manganese  is  then  pre- 
cipitated in  the  form  of  sesquioxide,  while  the  alumina  and 
glucina  are  dissolved  by  the  potash.  If,  however,  the  propor- 
tion of  manganese  be  considerable,  this  method  cannot  be 
used,  because  the  oxide  of  manganese  carries  down  with  it 


IRON.  23 

considerable  quantities  of  alumina  and  glucina.  In  this  case, 
the  liquid  must  be  mixed  with  sal-ammoniac  and  the  alumina 
and  glucina  precipitated  by  ammonia.  The  precipitate,  how- 
ever, always  contains  small  quantities  of  manganese,  which 
must  be  separated  by  subsequent  treatment  with  potash. 


SECTION    II. 

IRON. 

Eq,  28  or  350  j  Fe  (ferrum). 


The  most  remarkable  of  the  metals;  the  production  of  which, 
from  the  numerous  and  important  applications  it  possesses, 
appears  to  be  an  indispensable  condition  of  civilisation. 
Meteoric  masses  of  iron,  often  so  pure  as  to  be  malleable,  are 
found  widely  although  thinly  scattered  over  the  eartVs 
surface,  and  probably  first  attracted  the  attention  of  mankind 
to  this  metal.  Of  the  occurrence  of  metallic  iron  as  a  terres- 
trial mineral  in  situ,  the  best  established  instances  are  the 
species  of  native  iron  which  accompanies  the  Uralian  platinum, 
and  a  thin  vein  about  two  inches  in  thickness,  observed  in 
chlorite  slate,  near  Canaan  in  the  United  States.  In  a  state  of 
combination,  iron  is  extensively  diffused,  being  found  in  small 
quantity  in  the  soil,  and  in  most  minerals,  and  as  sulphide, 
oxide,  and  carbonate,  in  quantities  which  afford  an  inexhaust- 
ible supply  of  the  metal  and  its  preparations,  for  economical 
purposes. 

Iron  differs  from  all  other  metals  in  two  points,  which 
greatly  affect  the  methods  of  reducing  it.  Its  particles  agglu- 
tinate at  a  full  red  heat,  although  the  pure  metal  is  nearly 
infusible.  The  oxides  of  iron,  which  are  easily  reduced  by 
combustible  matter,  thus  yield  in  the  furnace  a  spongy  metallic 
mass,  which  may  admit  of  being  compacted  by  subsequent 

c  4 


24t  IRON. 

heating  and  hammering,  if  the  oxide  has  originally  been  free 
from  earthy  and  other  foreign  matter.  Such  probably  was 
everywhere  the  earliest  mode  of  treating  the  ores  of  iron,  and 
we  find  it  still  followed  among  rude  nations.  But  iron  is  also 
singular  in  forming,  at  an  elevated  temperature,  a  fusible 
compound  with  carbon  (cast  iron),  the  production  of  which 
facilitates  the  separation  of  the  metal  from  every  thing  extra- 
neous in  the  ore,  and  is  the  basis  of  the  only  method  of  extract- 
ing iron  extensively  practised. 

The  ore  of  iron  most  abundant  in  the  primary  formations 
is  the  black  oxide  or  magnetic  ore,  which  affords  the  most 
celebrated  and  valuable  irons  of  Sweden  and  the  north  of 
Europe,  but  of  which  the  application  is  greatly  circumscribed 
from  its  not  being  associated  with  coal.  In  the  secondary 
and  tertiary  formations,  the  anhydrous  and  hydrated  sesqui- 
oxide  of  iron,  red  and  brown  hematite,  occur  occasionally  in 
considerable  quantity,  often  massive,  reniform,  and  quite  pure, 
at  other  times  pulverulent  and  mixed  with  clay.  It  is  em- 
ployed to  some  extent  in  England  in  the  last  condition,  but 
only  for  the  purpose  of  mixing  with  the  more  common  ore. 
The  crystallised  carbonate  of  iron,  or  spathic  iron,  is  smelted  in 
some  parts  of  the  continent,  and  gives  an  iron  often  remark- 
able for  a  large  proportion  of  manganese.  The  celebrated 
iron  of  Elba  is  derived  from  specular  or  oligistic  iron,  a 
crystallised  sesquioxide.  But  the  consumption  of  all  these 
ores  is  inconsiderable,  compared  with  that  of  the  clay  iron- 
stone of  the  coal  measures.  This  is  the  carbonate  of  the 
protoxide  of  iron  mixed  with  variable  quantities  of  clay  and 
carbonates  of  lime,  magnesia,  &c. ;  it  is  often  called  the  argil- 
laceous carbonate  of  iron.  It  is  a  sedimentary  rock  wholly 
without  crystallisation,  resembhng  a  dark-coloured  limestone, 
but  of  higher  density,  from  2-936  to  3-471,  and  not  effer- 
vescing so  strongly  in  an  acid.  It  occurs  in  strata,  beds,  or 
bands,  as  they  are  also  named,  from  2  to  10  or  14  inches  in 
thickness,  alternating  with  beds  of  coal,  clay,  bituminous 


SMELTING    CLAY    IRON-STONE. 


25 


schist,  and  often  limestone.  The  proportion  of  iron  in  this 
ore  varies  considerably,  but  averages  about  30  per  cent.,  and 
after  it  has  been  calcined,  to  expel  carbonic  acid  and  water, 
about  40  per  cent.* 


SMELTING    CLAY    IRON-STONE. 


The  Ijlast   furnace,   in  which  the   ore  is  reduced,   is  of 
the  form  represented  below,  40  to  65  feet  in  height,  with 

rig.  2. 


*  Accurate  analyses  of  several  Scotch  varieties  of  this  ore  have  been  pub- 
lished by  Dr.  H.  Colquhoun  (Brewster's  Journal^  vii.  234  j  or  Dr.  Thomson's 
Outlines  of  Mineralogy  and  Geology^  i,  446) ;   and  of  the  French  ores,  by 


26  IRON. 

an  interior  diameter  of  from  14  to  17  feet  at  the  widest 
part.  The  cavity  of  the  furnace  is  entirely  filled  with  fuel 
and  the  other  materials,  which  are  continuously  supplied  from 
an  opening  near  the  top;  and  the  combustion  maintained 
by  air  thrown  in  at  two  or  more  openings,  called  tuyeres,  near 
the  bottom,  under  a  pressure  of  about  6  inches  of  mercury, 
from  a  blowing  apparatus,  so  as  to  maintain  the  whole  con- 
tents of  the  furnace  in  a  state  of  intense  ignition.  When  the 
air  to  support  the  combustion  has  attained  a  temperature  of 
600°  or  700°,  by  passing  through  heated  iron  tubes,  before 
it  is  thrown  into  the  furnace,  raw  coal  may  be  used  as  the 
fuel ;  but  with  cold  air,  the  coal  must  be  previously  charred 
to  expel  its  volatile  matter,  and  converted  into  coke,  other- 
wise the  heat  produced  by  its  combustion  is  insufficient. 
"With  the  ore  and  fuel,  a  third  substance  is  added,  generally 
limestone,  the  object  of  which  is  to  form  a  fusible  compound 
with  the  earthy  matter  of  the  ore ;  it  is,  therefore,  called  a 
flux.  Two  liquid  products  accumulate  at  the  bottom  of  the 
furnace,  namely,  a  glass  composed  of  the  flux  in  combination 
with  the  earthy  impurities  of  the  ore,  which  when  drawn  off 
forms  a  solid  slag,  and  the  carbide  of  iron,  or  metal,  which  is 
the  heavier  of  the  two.  It  may  be  drawn  from  observations 
made  by  Dr.  Clark,  in  1833,  on  the  working  of  the  Scotch 
blast  furnaces,  under  the  hot  blast,  that  the  relative  pro- 
portions of  the  materials,  including  air,  and  product  of  cast 
iron,  are  as  follows*  : — 


Coal 

Weight, 

5 

Roasted  iron-stone 

5 

Limestone     ..... 
Air 

Average  product  of  cast  iron 

1 

.       11 

2 

M.  Berthier,  in  his  Traite  des  essais  par  la  voie  seche,  ii.  252,  a  work  which  is 
invaluable  for  the  metallurgic  student,  and  Mitchell'e  Practical  Assaying^  8vo. 
•  Edinburgh  Phil.  Trans.  toI.  13. 


SMELTING    CLAY    IRON-STONE.  27 

^he  ultimate  fixed  products  are  the  slag  and  carburet  of 
iron,  but  the  formation  of  these  is  preceded  by  several  in- 
teresting changes  which  the  ore  successively  undergoes  in  the 
course  of  its  descent  in  the  furnace.  A  portion  of  the  oxide 
of  iron  is  certainly  reduced  to  the  metallic  state,  soon  after 
its  introduction,  in  the  upper  part  of  the  furnace,  by  carbonic 
oxide  and  volatile  combustible  matter ;  but  the  reduced  metal 
does  not  then  fuse.  A  large  portion  of  the  oxide  of  iron 
must  combine  also,  at  the  same  time,  with  the  silica  and 
alumina  present  in  the  ore,  which  act  as  acids,  and  a  glass 
be  formed,  the  oxide  of  iron  in  which  is  scarcely  reducible  by 
carbon.  But  this  injurious  effect  of  the  acid  earths  is  coun- 
teracted by  the  lime  of  the  flux,  which,  being  a  more  powerful 
base  than  oxide  of  iron,  liberates  that  oxide  from  the  glass 
when  the  proportions  of  the  materials  introduced  into  the 
furnace  are  properly  adjusted,  and  neutralises  the  silica;  so 
that  the  slag  eventually  becomes  a  silicate  of  lime  and  alumina, 
with  scarcely  a  trace  of  oxide  of  iron.  The  whole  oxide  of 
iron  comes  thus  to  be  exposed  to  the  reducing  action  of  the 
volatile  combustible,  and  consequently  the  whole  iron  is  pro- 
bably, at  one  time,  in  the  condition  of  pure  or  malleable  iron. 
But  when  the  metal  descends  somewhat  farther  in  the  fur- 
nace, it  attains  the  high  temperature  at  which  it  combines 
with  the  carbon  of  the  coke  in  contact  with  it,  and  it  fuses 
for  the  first  time,  in  the  form  of  carburet  of  iron.  It  has  not 
yet,  however,  attained  its  ultimate  condition.  When  it  reaches, 
in  its  descent,  the  region  of  the  furnace  where  the  heat  is 
most  intense,  its  carbon  reacts  on  the  silica,  alumina,  lime, 
and  other  alkaline  oxides  contained  in  the  fluid  slag  with 
which  it  is  accompanied,  reducing  portions  of  silicon,  alumi- 
num, calcium,  and  other  alkaline  metals,  which  combine  with 
the  iron.  The  proportion  of  carbon  replaced  by  silicon  and 
metallic  bases  is  generally  found  to  be  greater  in  iron  pre- 
pared by  the  hot  than  by  the  cold  blast,  owing,  it  is  presumed, 
to  the  higher  temperature  of  the  furnace  with  the  hot  blast. 


28  IRON. 

The  introduction  of  air  already  heated  to  support  the  com- 
bustion of  the  blast  furnace,  for  which  a  patent  was  obtained 
by  Mr.  J.  B.  Neilson,  has  greatly  reduced  the  proportion  of 
coal  required  to  smelt  a  given  weight  of  ore,  enabHng  the 
iron-master,  indeed,  to  effect  a  saving  of  more  than  three- 
fourths  of  the  coal  where  it  is  of  a  bituminous  quality.  The 
air  is  heated  between  the  blowing  apparatus  and  the  furnace, 
by  being  made  to  circulate  through  a  set  of  arched  tubes  of 
moderate  diameter,  heated  by  a  fire  beneath  them.  The  air 
can  be  heated  in  this  manner  to  low  redness,  or  to  near  1000**, 
but  there  is  found  to  be  no  proportional  advantage  in  raising 
its  temperature  much  above  the  melting  point  of  lead  (612°), 
which  is  already  higher  than  the  point  at  which  charcoal 
inflames.  Considering  the  great  weight  of  air  that  enters  the 
furnace,  the  temperature  of  that  material  must  greatly  affect 
the  whole  temperature  of  the  furnace,  particularly  of  the  lower 
part,  where  the  air  is  admitted,  and  which  part  it  is  desirable 
should  be  hottest.  Now  a  certain  elevated  temperature  is 
required  for  the  proper  smelting  of  the  ore,  and,  unless  attained 
in  the  fiimace,  the  fuel  is  consumed  to  no  purpose.  The 
removal  of  the  negative  influence  of  the  low  temperature  of 
the  air,  appears  to  permit  the  heat  to  rise  to  the  proper  point, 
which  otherwise  is  attained  with  difficulty  and  by  a  wasteful 
consumption  of  fuel.  Professor  Reich,  of  Freiberg,  has  ob- 
served that  heating  the  air  likewise  alters  the  relative  tem- 
peratures of  different  parts  of  the  furnace,  depressing  in  par- 
ticular, and  bringing  nearer  the  tuyeres,  the  zone  of  highest 
temperature.  The  admixture  of  steam  with  the  air  has,  he 
finds,  precisely  the  opposite  effect,  elevating  the  zone  of 
highest  temperature  in  the  furnace ;  so  that  the  effect  of  the 
hot  blast  may  be  exactly  neutralised  by  mixing  steam  with 
the  hot  air. 

Cast  iron.  —  The  fused  metal  is  run  into  channels  formed 
in  sand,  and  thus  cast  into  ingots  or  pigs,  as  they  are  called. 


WHITE    CAST    IRON.  29 

Cast  iron  is  an  exceedingly  variable  mixture  of  reduced  sub- 
stances, of  which  the  principal  is  iron  combined  with  carbon. 
The  theoretical  constitution  to  which  that  variety  of  it,  most 
definite  in  its  composition,  approaches,  is  the  following :  — 

WHITE    CAST    IRON. 

4  equivalents  of  iron    .  ,  .       94*9 

1  equivalent  of  carbon  ,  ,         5*1 


100-0 


The  difference  in  appearance  and  quality  of  the  varieties  of 
cast  iron  is  not  well  accounted  for  by  their  composition.  The 
grey  or  mottled  cast  iron,  forming  the  qualities  Nos.  1  and  2, 
presents  a  fracture  composed  of  small  crystals,  is  easily  cut  by 
the  file,  and  is  preferred  for  castings.  It  is  generally  sup- 
posed that  a  portion  of  uncombined  carbon  is  diffused  through 
the  iron  of  these  qualities,  in  the  form  of  graphite.  No.  3, 
or  white  cast  iron,  is  more  homogeneous ;  its  fracture  exhibits 
crystalline  plates,  like  that  of  antimony,  and  is  nearly  white ; 
it  is  exceedingly  hard  and  brittle. 

Malleable  iron. — The  great  proportion  of  cast  iron  manu- 
factured is  afterwards  refined,  or  converted  into  bar  or 
malleable  iron.  The  mode  of  effecting  this  conversion  varies 
with  the  nature  of  the  fuel.  Where  coal  or  coke  is  used,  as 
in  this  country,  the  process  consists  of  two  stages.  In  the 
first,  which  is  called  refining,  the  pig-iron  is  heated  in  contact 
with  the  fuel  in  small  low  furnaces  called  refineries,  while  air 
is  blown  over  its  surface  by  means  of  tuyeres.  The  effect  of 
this  operation  is  to  deprive  the  iron  of  a  great  portion  of  the 
carbon  and  nearly  all  the  silicon  associated  with  it.  The 
metal  thus  far  purified  is  run  out  into  a  trench,  and  suddenly 
cooled  by  pouring  cold  water  upon  it.  It  then  forms  a 
greyish- white  very  brittle  mass,  blistered  on  the  surface.     In 


30 


this  state  it  is  called  fine  metal.  It  is  then  ready  for  the 
second  and  principal  operation,  called  the  puddling  process, 
which  consists  in  heating  masses  of  the  iron  with  a  certain 
access  of  air  in  a  kind  of  reverberatory  furnace,  called  the 
puddling  furnace,  of  which  Fig.  3.  represents  a  vertical  sec- 
tion. This  furnace  has  four  doors,  two  of  which,  F  and  G, 
serve  for  the  introduction  of  fuel  to  the  grate ;  the  charge 
of  metal  is  introduced  at  E;  and  D  serves  for  the  insertion 
of  a  long  poker  or  spatula,  with  which  the  metal  is  stirred 
about.  The  hearth  of  the  furnace  has  an  aperture  B  at 
the  back,  for  removing  the  slag.  The  furnace  having  been 
brought  to  a  bright  red  heat,  about  four  or  five  hundred- 
weight of  fine  metal  is  introduced,  together  with  one  hun- 
dred-weight of  rich  scoriae  or  forge  cinders  (scale-oxide). 
The  metal  then  fuses,  and  in  this  state  the  workman  stirs 
it  about  with  the  poker,  so  as  to  expose  every  part  to  the 
flame.  The  carbon  is  thus  gradually  burnt  out,  partly  by 
the  direct  action  of  oxygen  in  the  flame,  and  partly  by 
cementation  with  the  oxide  of  iron ;  and  the  metal  becomes 


STEEL.  81 

less  fusible,  and  thick  and  tenacious,  so  that  it  sticks  together, 
and  is  easily  formed  into  four  or  five  large  balls,  called 
blooms.  In  this  condition  it  is  removed  by  tongs,  com- 
pressed into  a  cylindrical  form  by  a  few  blows  of  a  loaded 
hammer,  and  quickly  converted  into  a  bar,  by  pressing  it 
between  grooved  rollers.  The  tenacity  of  the  metal  is  further 
increased  by  welding  several  bars  together ;  a  faggot  of  bars 
is  brought  to  a  white  heat  in  an  oblong  furnace,  and  then 
extended  between  the  grooved  rollers  into  a  single  bar. 

The  texture  of  malleable  iron  is  fibrous.  Although  the 
purest  commercial  form  of  the  metal,  it  still  contains  about 
one-half  per  cent,  of  carbon,  with  traces  of  silicon  and  other 
metals. 

Pure  iron  may^  however,  be  obtained  by  introducing  into  a 
Hessian  crucible  4  parts  of  iron  wire  cut  into  small  pieces, 
and  1  part  of  black  oxide  of  iron;  placing  above  these  a 
mixtui'e  of  white  sand,  lime,  and  carbonate  of  potash,  in  the 
proportions  used  for  glass-making ;  covering  the  crucible  with 
a  closely  fitting  lid ;  and  exposing  it  to  a  very  high  tempera- 
ture. A  button  of  pure  metal  is  thus  obtained,  the  traces  of 
carbon  and  silicon  in  the  iron  having  been  removed  by  the 
oxygen  of  the  oxide.    (Mitscherlich.) 

Steel.  —  Only  the  best  qualities  of  malleable  iron,  those 
prepared  from  a  pure  ore,  and  reduced  by  means  of  charcoal, 
such  as  the  Swedish  iron,  are  converted  into  steel.  An  iron 
box  is  filled  with  flat  bars  of  such  iron  and  charcoal  powder, 
in  alternate  layers,  and  kept  at  a  red  heat  for  forty-eight 
hours,  or  longer.  The  surface  of  the  bars  is  found  after- 
wards to  be  blistered,  and  they  have  absorbed  from  1-3  to 
1*75  per  cent,  of  carbon.  This  is  the  process  of  cementa- 
tion. It  is  known  that  iron  can  be  converted  into  steel 
without  being  in  actual  contact  with  charcoal,  provided  the 
iron  and  charcoal  are  in  a  close  vessel  together,  and  oxygen 
be  present,  the  carbon  reaching  the  surface  of  the  metal  in 


33  IRON. 

the  form  of  carbonic  oxide  gas.  The  iron  becomes  harder  by 
this  change,  and  more  fusible,  but  can  still  be  hammered 
into  shape,  and  cut  with  a  file.  The  property  in  which  steel 
differs  most  from  soft  iron,  is  the  capacity  it  has  acquired  of 
becoming  excessively  hard  and  elastic,  when  heated  to  red- 
ness and  suddenly  cooled  by  plunging  it  into  cold  water  or  oil. 
This  hardness  makes  steel  invaluable  for  files,  knives,  and  all 
kinds  of  cutting  instruments.  But  the  steel,  when  hardened 
in  the  manner  described,  is  harder  than  is  required  for  most 
of  its  applications,  and  also  very  brittle.  Any  portion  of  its 
original  softness  can  be  restored  to  the  steel  by  heating  it  up 
to  particular  temperatures, — which  are  judged  of  by  the 
colour  of  the  film  of  oxide  upon  its  surface,  which  passes  from 
pale  yellow  at  about  430**,  through  straw  yellow,  bro\\Ti  yellow, 
and  red  purple  into  a  deep  blue  at  580**,  —  and  allowing  the 
steel  afterwards  to  cool  slowly.  Articles  of  steel  are  tempered 
in  this  manner. 

A  simple  and  expeditious  method  of  converting  crude  or 
pig-iron  into  malleable  iron  and  steel,  vnthout  the  aid  of  fuel, 
has  lately  been  proposed  by  Mr.  H.  Bessemer.  This  process 
consists  in  causing  cold  air  to  bubble  through  the  liquid  iron ; 
under  which  circumstances  the  oxygen  of  the  air  combines 
with  the  carbon  of  the  iron,  removing  it  in  the  form  of  car- 
bonic oxide,  and  generating  sufficient  heat  to  keep  the  iron  in 
the  liquid  state  without  external  heating,  and  to  sustain  the 
action  till  the  whole,  or  any  required  proportion,  of  the  car- 
bon is  burnt  away.  As  the  quantity  of  carbon  in  the  metal 
diminishes,  part  of  the  oxygen  combines  with  the  iron,  con- 
verting it  into  an  oxide,  which,  at  the  very  high  tem- 
perature then  existing  in  the  vessel,  melts,  and  forms  a 
powerful  solvent  for  the  earthy  bases  associated  with  the  iron. 
At  a  certain  stage  of  the  process,  the  whole  of  the  crude  iron 
is  said  to  be  converted  into  cast  steel  of  ordinary  quality. 
By  continuing  the  process,  the  steel  thus  formed  is  gradually 
deprived  of  its  small  remaining  portion  of  carbon,  and  passes 


PROPERTIES   OF   IRON.  33 

successively  from  hard  to  soft  steely  steely  iron,  and  ulti- 
mately to  very  soft  iron.* 

Properties  of  iron. — Iron  is  of  a  bluish- white  colour,  and 
admits  of  a  high  polish.  It  is  remarkably  malleable,  parti- 
cularly at  a  high  temperature,  and  of  great  tenacity.  Its 
mean  density  is  7'7,  which  is  increased  by  fusion  to  7'8439. 
When  kept  for  a  considerable  time  at  a  red  heat,  its  particles 
often  form  large  cubic  or  octohedral  crystals,  and  the  metal 
becomes  brittle.  Malleable  iron  softens  before  entering  into 
fusion,  and  in  this  state  it  can  be  welded,  or  two  pieces 
united  by  hammering  them  together.  The  point  of  fusion  of 
cast  iron  is  3479° ;  that  of  malleable  iron  is  much  higher. 
Cast-iron  expands  in  becoming  solid,  and  therefore  takes 
the  impression  of  a  mould  with  exactness.  Iron  is  attracted 
by  the  magnet  at  all  temperatures  under  an  orange-red  heat. 
It  is  then  itself  magnetic  by  induction,  but  immediately  loses 
its  polarity,  if  pure,  when  withdrawn  from  the  magnet.  If 
it  contains  carbon,  as  steel  and  cast  iron,  it  is  affected  less 
strongly,  but  more  durably,  by  the  proximity  of  a  magnet, 
becoming  then  permanently  magnetic.  Among  the  native 
compounds  of  iron,  the  black  oxide,  which  forms  the  load- 
stone, and  the  corresponding  sulphide,  are  those  which  share 
this  property  with  the  metal  in  the  highest  degree.  A  steel 
magnet  loses  its  polarity  at  the  boiling  point  of  almond  oil ;  a 
loadstone,  just  below  visible  ignition  (Faraday). 

Iron  reduced  from  the  oxide  by  hydrogen  at  a  heat  under 
redness,  forms  a  spongy  mass,  which,  when  exposed  to  air, 
takes  fire  spontaneously  at  the  usual  temperature,  oxide  of 
iron  being  reproduced  (Magnus).  But  iron,  in  mass,  appears 
to  undergo  no  change  in  dry  air,  and  to  be  incapable  of  decom- 
posing pure  water  at  ordinary  temperatures.     Nor  does  it 

*  Cliemical  Gazette,  1856.  p.  336. 
VOL.   II.  » 


31  IRON. 

appear  to  be  acted  upon  by  oxygen  and  water  together  ;  but 
the  presence  of  carbonic  acid  in  the  water  causes  the  iron  to 
be  rapidly  oxidated,  with  evolution  of  hydrogen  gas.  In  the 
ordinary  rusting  of  iron,  the  carbonate  of  the  protoxide 
appears  to  be  first  produced,  but  that  compound  gradually 
passes  into  the  hyd  rated  sesquioxide,  and  the  carbonic  acid 
is  evolved.  The  rust  of  iron  always  contains  ammonia, 
probably  absorbed  from  the  air ;  the  native  oxides  of  iron  also 
contain  ammonia.  Iron  remains  bright  in  solutions  of  the 
alkalies  and  in  lime-water,  which  appear  to  protect  it  from 
oxidation ;  but  neutral,  and  more  particularly  acid  salts, 
have  the  opposite  effect.  The  coiTosion  of  iron  under  water 
appears,  in  general,  to  be  immediately  occasioned  by  the 
formation  of  a  subsalt  of  that  metal  with  excess  of  oxide, 
the  acid  of  which  is  supplied  by  the  saline  matter  in  so- 
lution. Articles  of  iron  may  be  completely  defended  from 
the  injury  occasioned  in  this  way,  by  contact  with  the  more 
positive  metal  zinc,  as  in  galvanized  iron  (I.,  257),  while 
the  protecting  metal  itself  wastes  away  very  slowly.  Cast 
iron  is  converted  into  a  species  of  graphite  by  many  years' 
immersion  in  sea-water,  the  greater  part  of  the  iron  being 
dissolved  w  hile  the  carbon  remains.*  In  open  air,  iron  burns 
at  a  high  temperature  with  vivacity,  and  its  surface  becomes 
covered  with  a  fused  oxide,  which  forms  smithy  ashes.  Iron 
also  decomposes  steam  at  a  red  heat,  and  the  same  oxide 
is  formed  as  by  the  combustion  of  the  metal  in  air,  namely, 
the  magnetic  or  black  oxide,  FeO.FcgOg. 

Iron  dissolves  readily  in  diluted  acids,  by  substitution  for 
hydrogen,  which  is  evolved  as  gas.  Strong  nitric  acid  acts 
violently  upon  iron,  yielding  oxygen  to  it,  and  undergoing 
decomposition.     But  the  relations  of  iron  to  that  acid  when 


*  Mr.  Mallet  has  collected  much  information  respecting  the  corrosion  of 
iron,  in  his  First  Report  to  the  British  Association,  on  the  action  of  sea  and 
river  water  upon  cast  and  wroui;ht  ii'on,  1839. 


PASSIVE    CONDITION    OF    IRON.  35 

slightly  diluted   are  exceedingly  singular;    they  have  been 
particularly  studied  by  Professor  Schonbein. 

Passive  condition  of  iron. — Pure  malleable  iron,  such  as  a 
piece  of  clean  stocking  wire,  usually  dissolves  in  nitric  acid  of 
sp.  gr.  1-3  to  1-35,  with  effervescence;  but  it  may  be  thrown 
into  a  condition  in  which  it  is  said  by  Schonbein  to  be  passive, 
as  it  is  no  longer  dissolved  by  that  acid,  and  may  be  preserved 
in  it  for  any  length  of  time  without  change  : — 1.  By  oxidating 
the  extremity  of  the  wire  slightly,  by  holding  it  for  a  few 
seconds  in  the  flame  of  a  lamp,  and  after  it  is  cool  dipping  it 
gradually  in  the  nitric  acid,  introducing  the  oxidated  end  first. 
2.  By  dipping  the  extremity  of  the  wire  once  or  twice  in  con- 
centrated nitric  acid,  and  washing  it  with  water.  3.  By  placing 
a  platinum  wire  first  in  the  acid,  and  then  introducing  the 
iron  wire,  preserving  it  in  contact  with  the  former,  which  may 
afterwards  be  withdrawn.  4.  A  fresh  iron  wire  may  be  intro- 
duced in  the  same  manner  into  the  nitric  acid,  in  contact  with 
a  wire  already  passive ;  this  may  render  passive  a  third  wire, 
and  so  on.  5.  By  making  the  wire  the  positive  pole  or  zincoid 
of  a  voltaic  battery,  introducing  it  after  the  negative  pole  or 
chloroid  has  been  placed  in  the  acid.  Oxygen  gas  is  then 
evolved  from  the  surface  of  the  iron  wire,  without  combining 
with  it,  as  if  the  wire  were  of  platinum.  As  the  passive  state 
can  be  communicated  by  contact  of  passive  iron,  so  it  may  be 
destroyed  by  contact  Tvith  active  iron  (or  zinc)  undergoing,  at 
the  moment,  solution  in  the  acid.  If  passive  iron  be  made  a 
negative  pole  (chlorous)  in  nitric  acid,  it  also  ceases  to  resist 
solution.  The  indifference  to  chemical  action  exhibited  by 
iron  when  passive,  is  not  confined  to  nitric  acid  of  the  density 
mentioned,  but  extends  to  various  saline  solutions  which  are 
usually  acted  upon  by  iron.  An  indifference  to  nitric  acid  of 
the  same  kind  can  also  be  acquired  by  other  metals  as  well  as 
iron,  particularly  by  bismuth  (Dr.  Andrews),  but  in  a  much  less 
degree.  To  account  for  this  remarkable  phenomenon  various 
theories  have  been  proposed.     Schonbein  and  Wetzlar  attri- 

D   2 


36  IRON. 

bute  it  to  a  peculiar  electro-dynamic  condition  of  the  surface 
of  the  metal,  similar  to  that  of  the  platinum  in  Grove's  gas 
battery  (I.  268 — 270).  Mousson  attributes  it  to  a  coating  of 
nitrous  acid.  By  others  again  it  has  been  ascribed  to  a  peculiar 
antagonism  between  two  forces  acting  simultaneously  on  the 
metal,  the  one  tending  to  oxidate  it  at  the  expense  of  the  nitric 
acid,  the  other  to  cause  it  to  take  the  place  of  hydrogen  in  the 
nitrate  of  water,  just  as  when  it  dissolves  in  sulphuric  acid.* 
But  perhaps  the  most  probable  explanation  is  that  which  attri- 
butes the  passive  condition  of  iron  to  the  formation  on  its  sur- 
face of  a  thin  film  of  anhydrous  ferric  oxide,  similar  to  specular 
iron.  This  view  is  supported  by  the  fact  that  iron  which  has 
been  ignited,  and  is  therefore  completely  covered  with  black 
oxide,  exhibits  tlie  same  characters,  excepting  that,  from  the 
greater  thickness  of  the  coating,  the  passive  state  is  more 
complete.  It  may  also  be  observed,  that  iron  becomes  passive 
only  in  liquids  which  give  up  oxygen,  and  that  in  the  voltaic 
circuit  it  becomes  passive  precisely  under  the  circumstances 
in  which  it  is  exposed  to  oxidation,  i.  e.  when  it  is  made  the 
zincoid  or  positive  pole,  and  that  it  becomes  active  again  when 
made  the  negative  pole,  that  is  to  say,  when  the  oxide  is 
reduced.  The  same  view  is  supported  by  the  observation  that 
iron  rendered  passive  in  nitric  acid  immediately  begins  to  dis- 
solve on  the  addition  of  hydrochloric  acid. 


PROTOCOMPOUNDS    OF    IRON  ;     FERROUS    COMPOUNDS. 

Protoxide  of  iron,  Ferrous  oxide ;  FeO  ;  36  or  450.  —  Iron 
appears  to  admit  of  three  degrees  of  oxidation,  the  protoxide 

*  Dr.  Andrews  indeed  concludes  from  observation,  that  the  ordinary 
chemical  action  of  a  hjdrated  acid  upon  the  metals  which  dissolve  in  it,  is  in 
general  diminished,  when  the  acid  is  concentrated,  by  the  voltaic  association 
of  these  metals  with  such  metals  as  gold,  platinum,  &c. ;  while,  on  the  con- 
trary, it  is  increased  when  the  acid  is  diluted. — Trans,  of  the  Koyal  Irish 
Academy,  1838  ;  or,  Bccquercl,  vol.  v.  pt.  2,  p.  187. 


FERROUS    COMPOUNDS.  37 

and  sesquioxide,  whicli  are  both  basic  and  correspond  respec- 
tively with  manganous  and  manganic  oxide,  and  ferric  acid. 
The  protoxide  is  not  easily  obtained  in  a  dry  state,  from  the 
avidity  with  which  it  absorbs  oxygen.  The  purest  anhydrous 
protoxide  is  obtained  by  igniting  the  oxalate  out  of  contact  of 
air;  but  even  this,  according  to  Liebig,  contains  a  small 
quantity  of  metallic  iron.  The  protoxide  exists  in  the  sulphate 
and  other  salts  of  iron,  formed  when  the  metal  dissolves  in  an 
acid  with  evolution  of  hydrogen. 

Solutions  of  ferrous  salts  have  a  green  colour.  Potash  or 
soda  added  to  them  throws  down  the  protoxide  as  a  white 
hydrate,  which  becomes  black  on  boiling,  from  loss  of  water. 
The  colour  of  the  white  precipitate  changes  by  exposure  to 
air,  to  grey,  then  to  green,  bluish  black,  and  finally  to  an 
ochrey  red,  when  it  is  entirely  sesquioxide.  Ammonia  exer- 
cises a  similar  action,  but  does  not  precipitate  the  whole  of 
the  oxide,  because  the  precipitate  dissolves  in  the  ammoniacal 
salt  produced.  Alkaline  carbonates  form  a  precipitate  of 
carbonate  of  iron,  which  is  white  at  first,  but  soon  becomes  of 
a  dirty  green,  and  undergoes  the  same  subsequent  changes 
from  oxidation.  Ferrous  salts  are  not  precipitated  by  hydro- 
sulphuric  acid,  the  sulphide  of  iron  being  dissolved  by  strong 
acids,  but  give  a  black  sulphide  with  solutions  of  alkaline  sul- 
phides. They  give  a  white  precipitate  with  ferrocyanide  of 
potassium,  which  gradually  becomes  of  a  deep  blue  when 
exposed  to  air ;  with  the  ferricyanide,  a  precipitate  which  is 
at  once  of  an  intense  blue,  being  one  of  the  varieties  of 
Prussian  blue.  The  infusion  of  gall-nuts  does  not  afiect  a 
solution  of  the  protoxide  of  iron  when  completely  free  from 
sesquioxide. 

Protosulphide  of  iron  is  prepared  by  heating  to  redness,  in 
a  covered  crucible,  a  mixture  of  iron  filings  and  crude  sulphur, 
in  the  proportion  of  7  of  the  former  to  4  of  the  latter.  It 
dissolves  in  sulphuric  and  hydrochloric  acids,  with  evolution  of 
hydrosulphuric  acid  gas  (I.  420.). 

D  3 


SS  IRON. 

A  subsulphide  of  iron,  ^^cfi,  appears  to  be  formed  wlien  tlic 
sulphate  of  iron  is  reduced  by  hydrogen^  one-half  of  the  sul- 
phur coming  off  in  the  form  of  sulphurous  acid.  This  sub- 
sulphide  is  analogous  to  the  subsulphidcs  of  copper  and  lead, 
which  crystallise  in  octahedi'ons. 

Protochloride  of  iroii  crystallises  with  4H0,  and  is  very 
soluble.  Like  all  soluble  ferrous  salts,  it  is  of  a  green 
colour,  gives  a  green  solution,  and  has  a  great  avidity  for 
oxygen. 

Protiodide  of  iron  is  formed  when  iodine  is  digested  with 
water  and  iron  wire,  the  latter  being  in  excess,  and  is  obtained 
as  a  crystalliue  mass  by  evaporating  to  dryness.  It  was 
introduced  into  medical  use  by  Dr.  A.  T.  Thomson.  A  piece 
of  iron  wire  is  placed  in  the  solution  of  this  salt  to  preserve  it 
from  oxidising.  The  protiodide  of  iron  dissolves  a  large 
quantity  of  iodine,  without  becoming  periodide,  as  the  excess 
of  iodine  may  be  precipitated  by  starch. 

Protocyanide  of  iron  C2NFe  or  FeCy,  is  as  difficult  to 
obtain  as  the  protoxide  of  iron.  "When  cyanide  of  potassium  is 
added  to  a  protosalt  of  iron,  a  yellowish-red  precipitate  appears, 
which  dissolves  in  an  excess  of  the  alkaline  cyanide,  and  forms 
the  ferrocyanide  of  potassium  (I.,  529.).  A  grey  powder  re- 
mains on  distilling  the  ferrocyanide  of  ammonium  at  a  gentle 
heat ;  and  a  white  insoluble  substance  on  digesting  recently 
precipitated  prussian  blue  in  sulphuretted  hydi'ogen  water, 
contained  in  a  well-stopped  phial ;  these  products,  although 
they  differ  considerably  in  properties,  have  both  been  looked 
upon  as  protocyanide  of  iron.  This  compound  is  also  obtained 
as  a  white  deposit  on  boiling  an  aqueous  solution  of  hydro- 
ferrocyanic  acid,  HgFeCyg.  The  same  solution  heated  with  red 
oxide  of  mercury  forms  cyanide  of  mercury  and  white  proto- 
cyanide of  iron.  The  most  remarkable  property  of  this  cy- 
anide is  its  tendency  to  combine  with  other  cyanides  of  all 
classes,  and  to  form  double  cyanides,  or  to  enter  as  a  con- 
stituent into  the  salt-radicals  ferrocyanogen  and  ferricyanogen, 
CyaEe  and  CjoFe^, 


FERROUS    COMPOUNDS,  39 

Hijdroferrocyanic  acid;  H2reCy3  or  2HCy,FeCy.  This 
compound  was  discovered  by  Mr.  Porrett.  It  may  be  ob- 
tained by  decomposing  ferrocyanide  of  barium  witb  sulphuric 
acid,  or  ferrocyanide  of  potassium  witb  an  alcoholic  solution 
of  tartaric  acid,  or  ferrocyanide  of  lead  with  hydrosulphuric 
acid.  It  is  soluble  in  water  and  alcohol,  insoluble  in  ether, 
and  crystallises  by  spontaneous  evaporation  in  cubes  or  four- 
sided  prisms,  or  sometimes  in  tetrahedrons.  When  dry,  it 
may  be  kept  for  a  long  time  without  alteration  in  close 
vessels;  but  is  decomposed  on  exposure  to  the  air  with 
evolution  of  hydrocyanic  acid,  and  formation  of  prussian  blue. 

Hydroferrocyanic  acid  unites  with  most  salifiable  bases, 
forming  the  salts  called  ferrocyanides,  whose  general  formula 
is  M2reCy3,  the  symbol  M  denoting  a  metal.  The  ferro- 
cyanides  of  ammonium,  potassium,  sodium,  barium,  stron- 
tium, calcium,  and  magnesium,  dissolve  readily  in  water ;  the 
rest  are  insoluble  or  sparingly  soluble.  Some  of  them,  as  the 
copper  and  uranium  salts,  are  very  highly  colom*ed.  Ferro- 
cyanide of  potassium  has  been  already  described  (I.  529.). 

Ferrocyanide  of  potassium  and  iron ;  Kre2Cy3  =  (KFe), 
(CygFe). — The  bluish- white  precipitate  which  falls  on  testing 
a  protosalt  of  iron  with  the  ferrocyanide  of  potassium  or  yellow 
prussiate  of  potash,  e.  g.y  with  the  protochloride : 

KaFeCyg  +  FeCl  =  KCl  +  KFcaCya- 

It  is  also  obtained  in  the  form  of  a  white  crystalline  salt 
(mixed  with  bisulphate  of  potash),  in  the  preparation  of  hydro- 
cyanic acid,  by  distilling  ferrocyanide  of  potassium  with  dilute 
sulphuric  acid  : 

2K2FeCy3  +  6S03  +  6HO  =  3(KO,HO,2S03)  +3HCy  F-KFcaCy,. 
Exposed  to  the  air,  it  absorbs  oxygen  and  becomes  blue. 
It  then  affords  ferrocyanide  of  potassium  to  water,  and  after 
all  soluble  salts  are  removed,  a  compound  remains,  which 
Liebig  names  the  basic  sesquiferrocyanide  of  iron,  and  repre- 
sents by  the   formula  Fe4.3(Cy3Fe) -f  FegOg,  corresponding, 

D   4 


40  IRON. 

as  will  be  seen  hereafter,  with  1  eq.  of  prussian  blue  +  1  eq. 
of  sesquioxide  of  iron.  This  basic  compound  is  dissolved 
entirely  by  continued  washing,  and  affords  a  beautiful  deep  blue 
solution.  The  addition  of  any  salt  causes  the  separation  of 
this  compound.  Its  solution  may  be  evaporated  to  dryness 
without  decomposition.  The  white  ferrocyanide  of  iron  and 
potassium  likewise  turns  blue  when  treated  with  chlorine- 
water  or  nitric  acid,  being  thereby  converted  into  fern- 
cyanide  of  iron  and  potassium  (KFe4Cy6). 

2KFe2Cy3  +  CI  =  KFe^Cyg  +  KCl. 

This  latter  compound,  which  when  dry  is  of  a  beautiful 
violet  colour,  may  be  regarded  as  ferricyanide  of  potassium 
K3re2Cy6,  in  which  2  eq.  of  potassium  are  replaced  by  iron 
(Williamson) . 

Ferricyanide  of  iroUy  TkimbuIVs  blue;  !Fe3(Cy6Fe2).  —  This 
is  the  beautiful  blue  precipitate  which  falls  on  adding  the 
ferricyanide  of  potassium  (red  prussiate  of  potash)  to  a  proto- 
salt  of  iron.  It  is  formed  by  the  substitution  of  3  eq.  of  iron 
for  the  3  eq.  of  potassium  of  the  latter  salt  (I.  530).  The 
same  blue  precipitate  may  be  obtained  by  adding  to  a  proto- 
salt  of  iron  a  mixture  of  yellow  prussiate  of  potash,  chloride 
of  soda,  and  hydrochloric  acid.  The  tint  of  this  blue  is 
lighter  and  more  delicate  than  that  of  prussian  blue.  It  is 
occasionally  used  by  the  calico-printer,  who  mixes  it  with 
permuriate  of  tin,  and  prints  the  mixture,  which  is  in  a  great 
measure  soluble,  upon  Turkey-red  cloth,  raising  the  blue 
colour  afterwards  by  passing  the  cloth  through  a  solution  of 
chloride  of  lime  containing  an  excess  of  lime.  The  chief 
object  of  that  operation  is  indeed  different,  namely,  to  dis- 
charge the  red  and  produce  white  patterns,  where  tartaric 
acid  is  printed  upon  the  cloth ;  but  it  has  also  the  effect  in- 
cidentally of  precipitating  the  blue  pigment  and  peroxide  of 
tin  together  on  the  cloth,  by  neutralising  the  acid  of  the  pre- 
muriate  of  tin.     This  blue  is  believed  to  resist  the  action  of 


FERROUS    COMPOUNDS.  41 

alkalies  longer  than  ordinary  prnssian  blue.  It  is  distin- 
guished from  Prussian  blue  by  yielding,  when  treated  with 
caustic  potash  or  carbonate  of  potash,  a  solution  of  ferro- 
cyanide  of  potassium,  and  a  residue  of  ferroso-ferric  oxide  : 

SFe^Cye  +  4K0  =  SK^FeCy,  +  ^630, ; 

whereas  prussian  blue  treated  in  the  same  manner  yields 
ferric  oxide  (Williamson). 

Carbonate  of  iron  is  obtained  on  adding  carbonate  of  soda 
to  the  protosulphate  of  iron,  as  a  white  or  greenish- white  pre- 
cipitate, which  may  be  washed  and  preserved  in  a  humid  con- 
dition in  a  close  vessel,  but  cannot  be  dried  without  losing 
carbonic  acid  and  becoming  sesquioxide  of  iron.  It  is  soluble, 
like  the  carbonate  of  lime,  in  carbonic  acid  water,  and  exists 
under  that  form  in  most  natm-al  chalybeates.  Carbonate  of 
iron  occurs  also  crystallised  in  the  rhombohedral  form  of  calc- 
spar,  forming  the  mineral  spathic  iron,  which  generally  con- 
tains portions  of  the  carbonates  of  lime,  magnesia,  and  man- 
ganese. It  is  generally  of  a  cream  colour  or  black,  and  its 
density  rarely  exceeds  3*8.  This  anhydrous  carbonate  does 
not  absorb  oxygen  from  the  air.  Carbonate  of  iron  is  also 
the  basis  of  clay  iron-stone.  There  is  no  carbonate  of  the 
sesquioxide. 

Protosulphate  of  iron.  Ferrous  sulphate.  Green  vitriol,  Cop- 
peras;  FeO.SOg,  HO  +  6H0;  7Q  4-  63  or  950  +  787-5.— 
This  salt  may  be  formed  by  dissolving  iron  in  sulphuric  acid 
diluted  with  4  or  5  times  its  bulk  of  water,  filtering  the  solu- 
tion while  hot,  and  setting  it  aside  to  crystallise.  But  the 
large  quantities  of  sulphate  of  iron  consumed  in  the  arts  are 
prepared  simultaneously  with  alum,  by  the  oxidation  of  iron 
pyrites  (I.  606). 

The  commercial  salt  forms  large  crystals,  derived  from  an 
oblique  rhomboidal  prism,  which  effloresce  slightly  in  dry  air, 
and,  when  at  all  damp,  absorb  oxygen  and  become  of  a  rusty 


43  IRON. 

red  colour;  hence  the  origin  of  the  Erench  term  couperose 
applied  to  this  salt^  and  comipted  in  our  language  into  cop- 
peras. If  these  crystals  be  crushed  and  deprived  of  all  hygro- 
metric  moisture  by  strong  pressure  between  folds  of  cotton 
cloth  or  filter  paper^  they  may  afterwards  be  preserved  in  a 
bottle  without  any  change  from  oxidation.  Of  the  7H0  which 
sulphate  of  iron  contains,  it  loses  6H0  at  238°,  but  retains  1  eq. 
even  at  535°.  It  may,  however,  be  rendered  perfectly  anhy- 
drous, with  proper  caution,  without  any  appreciable  loss  of 
acid.  The  anhydrous  salt  is  also  obtained  in  very  small 
crystalline  scales  by  immersing  the  hydrated  crystals  in 
strong  boiling  sulphuric  acid,  and  leaving  the  liquid  to  cool. 
The  salt  was  observed  by  Mitscherlich  to  crystallise  at  176°, 
with  4H0,  in  a  right  rhombic  prism,  like  the  corresponding 
sulphate  of  manganese.  "When  its  solution  containing  an  excess 
of  acid  is  evaporated  by  heat,  a  saline  crust  is  deposited, 
which,  according  to  Kuhn,  contains  3110.  The  sulphate  of 
iron  appears  to  form  neither  acid  nor  basic  salts.  One  part 
of  copperas  requires  to  dissolve  it,  the  following  quantities 
of  water,  at  the  particular  temperatures  indicated  above 
each  quantity,  according  to  the  observations  of  Brandes  and 
Firnhaber : — 

50°       59°     75-2°    109-1.°  111°     110-0°  183-2°    191°    212° 
1-64     1-13      0-87     0-6G      Oil      038      0-37      027     0-30 

Ferrous  sulphate  undergoes  decomposition  at  a  red  heat, 
changing  into  ferric  sulphate,  and  leaves,  after  all  the  acid 
is  expelled,  the  red  sesquioxide  known  as  colcothar.  This 
sulphate,  like  all  the  magnesian  sulphates,  forms  with  sul- 
phate of  potash  a  double  salt  containing  6H0.  A  solution  of 
the  sulphate  of  iron  absorbs  nitric  oxide,  and  becomes  quite 
black ;  according  to  Peligot,  it  takes  up  the  gas  in  the  pro- 
portion of  9  parts  to  100  anhydrous  salt,  or  one-fourth  of  an 
equivalent  (1.,  342). 

Protonitrate  of  iron.    Ferrous  nitrate,  may   be  formed  by 


FERRIC    COMPOUNDS.  43 

dissolving  the  protosulpliide  in  cold  dilute  nitric  acid;  the 
solution  evaporated  in  vacuo  yields  pale  green^  very  soluble 
crystals.  The  solution  of  the  neutral  salt  is  decomposed  near 
the  boiling  heat^  with  evolution  of  nitric  acid  and  copious  pre- 
cipitation of  a  ferric  subnitrate.  Iron  turnings  dissolve  in  dilute 
nitric  acid  and  form  the  same  salt,  without  evolution  of  gas, 
the  water  and  acid  being  decomposed  in  such  a  manner  as 
to  form  ammonia,  at  the  same  time  that  they  oxidate  the 
iron. 

'  Protoacetate  of  iron,  Ferrous  acetate,  is  obtained  by  dis- 
solving the  metal  or  its  sulphide  in  acetic  acid.  It  forms 
small  green  prisms  which  decompose  very  readily  in  the  air. 

Tartrate  of  potash  and  iron,  Potassio -ferrous  tartrate,  is 
prepared  by  boiling  bitartrate  of  potash  with  half  its  weight 
of  iron  turnings  and  a  small  quantity  of  water.  Hydrogen  is 
evolved,  and  a  white,  granular,  sparingly  soluble  salt  formed 
which  blackens  in  the  air  from  absorption  of  oxygen.  It  is 
used  medicinally.  The  iron  of  this  salt  is  not  precipitated  by 
hydrate  or  carbonate  of  potash. 


SESQUICOMPOUNDS    OF    IRON;    FERRIC    COMPOUNDS. 

Sesquioxide  of  iron ;  Peroxide  of  iron ;  Ferric  oxide,  80  or 
1000.  —  Occurs  very  abundantly  in  nature  :  1.  as  oligistic  or 
specular  iron,  in  crystals  derived  from  a  rhombohedron  very 
near  the  cube,  which  are  of  a  brilliant  metallic  black  and 
highly  iridescent.  Their  powder  is  red ;  their  density,  from 
5-01  to  5-22.  This  oxide  forms  the  celebrated  Elba  ore. — 
2.  As  red  hematite,  in  fibrous,  mammillated,  or  kidney-shaped 
masses,  of  a  dull  red  colour,  very  hard,  and  of  sp.  gr.  from  4*  8 
to  5*0.  This  mineral  when  cut  forms  the  burnishers  of  blood- 
stone.— 3.  also  in  combination  with  water,  as  brown  hematite, 
which  is  much  more  abundantly  diflPused  than  the  anhydrous 
sesquioxide,  the  granular  variety  supplying,  according  to  M. 


44  IRON. 

BertMer,  more  than  three-fourtlis  of  the  iron-fumaces  in 
France.  Its  density  is  3*922;  its  powder  is  brown  vnth  a 
shade  of  yellow^  and  it  dissolves  readily  in  acid,  which  the 
anhydrous  sesquioxide  does  not.  From  analyses  by  Dr. 
Thomson  and  M.  Berthier,  this  mineral  appears  to  unite  with 
1  eq.  of  water,  as  HO.Fe203,  analogous  to  the  magnetic  oxide 
of  iron,  FeO.Fe203.  The  hydrated  sesquioxide  produced  by  the 
oxidation  of  iron  pyrites,  of  which  it  retains  the  form,  contains 

1  eq.  of  water,  or  lO'Sl  percent.,  and  that  from  the  oxidation 
of  the  carbonate  of  iron,  3  eq.  of  water,  or  14' 71  per  cent.,  to 

2  eq.  of  sesquioxide  (Mitscherlich,  Lehrbuch,  II.  23,  1840). 
The  hydrate  is  the  yellow  colouring  matter  of  clay,  and  with 
silica  and  clay  it  forms  the  several  varieties  of  ochre. 

When  metallic  iron  is  oxidated  gradually  in  a  large  quantity 
of  water,  there  forms  around  it  a  light  precipitate  of  a  bright 
orange  yeUow  colour,  which,  according  to  Berzelius,  is  a  ferric 
hydrate,  and  of  which  the  empirical  formula  is  2Fe203  +  3HO, 
the  usual  composition  of  broT\-n  hematite.  When  iron  is 
oxidated  in  deep  water,  it  is  converted,  according  to  E.  Davy, 
into  the  magnetic  oxide,  which  is  possibly  formed  by  cemen- 
tation from  the  hydrated  sesquioxide.  The  hydrated  sesqui- 
oxide is  also  obtained,  by  precipitation  from  ferric  salts,  by 
ammonia  and  by  hydrated  or  carbonated  alkali;  but  never 
pure,  as  when  an  insufficient  quantity  of  alkali  is  added,  a  sub- 
salt  containing  acid  is  precipitated;  and  wlien  the  alkali  is 
added  in  excess,  a  portion  of  it  goes  down  in  combination 
with  the  oxide,  and  cannot  be  entirely  removed  by  washing. 
When  ammonia  is  used,  the  water  and  excess  of  the  precipi- 
tant may  be  expelled  by  ignition,  and  the  pure  sesquioxide 
obtained.  The  latter  is  not  magnetic,  and  after  ignition  dis- 
solves mth  difficulty  in  acids.  When  ignited  strongly,  it 
loses  oxygen  and  becomes  magnetic. 

Ferric  oxide  and  its  compounds  are  stiictly  isomorphous 
with  alumina  and  the  compounds  of  that  earth,  and  remark- 
ably analogous  to  them  in  properties.     It  is  a  weak  base. 


FERRIC    COMPOUNDS.  45 

of  whicli  the  salts  have  a  strong  acid  reaction,  and  are 
decomposed  by  all  the  magnesian  carbonates,  as  well  as  by 
the  magnesian  oxides  themselves.  The  solutions  of  its  salts, 
which  are  neutral  in  composition,  have  generally  a  yellow  tint ; 
but  they  are  all  capable,  when  rather  concentrated,  of  dissolv- 
ing a  great  excess  of  ferric  oxide,  and  then  become  red.  Very 
dilute  solutions  of  the  neutral  salts  of  ferric  oxide  are  decom- 
posed by  ebullition,  and  the  oxide  entirely  precipitated,  the 
acid  of  the  salt  then  uniting  with  water  as  a  base  ( S cheer er). 

Iron  is  most  conveniently  distinguished  by  tests,  or  pre- 
cipitated for  quantitative  estimation,  when  in  the  state 
of  sesquioxide.  The  solution  of  a  ferrous  salt  is  usually 
oxidised  by  transmitting  a  current  of  chlorine  through  it,  or 
by  adding  to  it,  at  the  boiling  point,  nitric  acid,  in  small 
quantities,  so  long  as  eflPervescence  is  occasioned  from  the 
escape  of  nitric  oxide.  Alkalies  and  alkaline  carbonates  throw 
down  a  red-brown  precipitate  of  hydrated  sesquioxide.  Hy^ 
drosulphuric  acid  converts  a  sesquisalt  of  iron  into  a  proto- 
salt,  with  precipitation  of  sulphur.  Ferrocyanide  of  potassium 
throws  down  prussian  blue,  but  the  ferricyanide  has  no 
effect  upon  ferric  salts  beyond  slightly  changing  the  colour 
of  the  solution.  Suljjhocyanide  of  potassium  produces  a  deep 
wine-red  solution  with  ferric  salts,  which  becomes  perfectly 
colourless  when  considerably  diluted  with  water,  provided 
the  iron  salt  is  not  in  great  excess.  Infusion  of  gall-nuts 
produces  a  bluish-black  precipitate  —  the  basis  of  common 
writing  ink. 

A  remarkable  insoluble  modification  of  the  hydrated  sesqui- 
oxide is  produced  by  boiling  the  ordinary  hydrate  (precipitated 
from  the  chloride  by  ammonia)  in  water  for  7  or  8  hours. 
The  colour  then  changes  from  ochre-yellow  to  brick-red,  and 
the  hydrate  thus  altered  is  scarcely  acted  upon  by  strong  boil- 
ing nitric  acid,  and  but  very  slowly  by  hydrochloric  acid.  In 
acetic  acid,  or  dilute  nitric  or  hydrochloric  acid,  it  dissolves, 
forming  a  red  liquid,  which  is  clear  by  transmitted  but  turbid 


46  IRON. 

by  reflected  light ;  is  precipitated  by  tlie  smallest  quantity  of 
an  alkali-salt  or  a  sulphate ;  and  on  addition  of  strong  nitric  or 
hydrochloric  acid,  yields  a  red  granular  precipitate  ^vhich 
re-dissolves  on  diluting  the  liquid  -with  water.  The  modified 
hydrate  does  not  form  prussian  blue  with  ferrocyanide  of  po- 
tassium and  acetic  acid.  It  appears  to  be  FcoOg.HO,  the 
ordinary  precipitated  hydrate,  after  drying  in  vacuo,  being 
2Fe203.3IIO.  This  insoluble  hydrate  is  likewise  precipi- 
tated when  a  solution  of  the  ordinary  hydrate  in  acetic  acid  is 
rapidly  boiled.  The  same  solution,  if  kept  for  some  time  at 
212°  in  a  close  vessel,  becomes  light  in  colour,  no  longer 
forms  prussian  blue  with  ferrocyanide  of  potassium,  or  exhibits 
any  deepening  of  colour  on  addition  of  a  sulphocyanide ; 
strong  hydi'ochloric  or  nitric  acid,  or  a  trace  of  an  alkali-salt, 
or  sulphuric  acid,  throws  down  all  the  ferric  oxide  in  the  form 
of  the  insoluble  hydrate.*  It  has  also  been  observed  that 
ferric  hydrate  becomes  crystalline  and  less  soluble  by  long 
immersion  in  water,  and  by  exposure  to  a  low  temperature. 

Black  or  magnetic  oxide  of  iron,  Ferroso -ferric  oxide, 
FeO.FcaOa,  an  important  ore  of  iron,  is  a  compound  of  the 
two  oxides.  It  crystallises  in  regular  octohcdrons.  In  this 
compound,  the  sesquioxide  of  iron  may  be  replaced  by  alu- 
mina and  by  oxide  of  chromium,  and  the  protoxide  of  iron  by 
oxide  of  zinc,  magnesia,  and  protoxide  of  manganese,  with- 
out change  of  form.  It  was  produced  artificially,  by  Liebig 
and  Wohler,  by  mixing  the  dry  protochloride  of  iron  with 
an  excess  of  carbonate  of  soda,  calcining  the  mixture  in  a 
crucible,  and  treating  the  mass  with  water.  The  double 
oxide  then  remains  as  a  black  powder,  which  may  be  washed 
and  dried  without  further  oxidation.  The  same  chemists,  by 
dissolving  the  black  oxide  in  hydrochloric  acid,  and  preci- 
pitating by  ammonia,  obtained  a  hydrate  of  the  double  oxide. 
It  was  attracted  by  the  magnet,  even  when  in  the  state  of  a 

»  Pean  de  St.  Gilles,  Ann.  Clt.  Phjs.  [3],  xlvi.  47. 


FERRIC    COMPOUNDS.  47 

flocculent  precipitate  suspended  in  water.  When  ignited  and 
anhydrous,  this  double  oxide  is  much  more  magnetic  than 
iron  itself. 

Scale-OMde,  6Fe0.re2  03. — When  iron  is  heated  to 
redness  in  contact  with  air,  two  layers  of  scale-oxide  are 
formed,  which  may  be  easily  separated.  The  inner  layer, 
which  has  the  composition  just  given,  is  blackish  grey,  porous, 
brittle,  and  attracted  by  the  magnet.  The  outer  layer  con- 
tains a  larger  proportion  of  ferric  oxide ;  it  is  of  a  reddish 
iron-black  colour,  dense,  brittle,  yields  a  black  powder,  and  is 
more  strongly  attracted  by  the  magnet  than  the  inner  layer. 
The  proportion  of  ferric  oxide  in  the  outer  layer  is  between 
32  and  37  per  cent.,  and  on  the  very  surface  as  much  as 
52*8  per  cent.  (Mosander).  The  specific  gravity  of  the  scale- 
oxide  is  5-48  (Boullay). 

Sesquisulphide  of  iron,  or  Ferric  sulphide,  Yq^  S3,  corre- 
sponding with  the  sesquioxide,  may  be  prepared  by  pouring  a 
solution  of  a  sesquisalt  of  iron,  drop  by  drop,  into  a  solution 
of  an  alkaline  sulphide,  the  latter  being  preserved  in  excess. 
At  a  low  red  heat,  it  loses  2-9ths  of  its  sulphur,  and  becomes 
magnetic  pyrites.  The  common  yellow  iron  pyrites  is  the 
bisulphide  of  iron.  It  crystallises  in  cubes  or  other  forms  of 
the  regular  system;  its  density  is  4*981.  It  may  be  formed 
artificially  by  mixing  the  protosulphide  with  half  its  weight 
of  sulphur,  and  distilling  in  a  retort  at  a  temperature  short  of 
redness.  The  metallic  sulphide  combines  with  a  quantity  of 
sulphur  equal  to  that  which  it  abeady  possesses,  and  forms  a 
bulky  powder  of  a  deep  yellow  colour  and  metallic  lustre, 
upon  which  sulphuric  and  hydrochloric  acids  have  no  action. 
This  sulphide  appears  to  be  of  a  stable  nature,  but  the  lower 
sulphides  of  iron  oxidate,  when  moistened,  with  great  avidity. 
Stromeyer  found  the  native  magnetic  sulphide  of  iron  to  con- 
sist of  100  parts  of  iron  combined  with  68  of  sulphur;  and 
the  sulphide  left  on  distilling  iron  with  sulphur  at  a  high 
temperature,  to  be  of  the  same   composition.     It  may  be 


48  IRON. 

viewed  as  BFeS.FcaSg  (Berzelius).  It  is  said  to  be  this 
compound  which  is  almost  always  formed  when  sulphide  of 
iron  is  prepared  in  the  usual  manner. 

Sesquichloride  of  iron.  Ferric  chloride,  Fcg  CI3,  is  formed 
when  iron  is  burned  in  an  excess  of  chlorine.  It  is  volatile 
at  a  red  heat.  Its  solution,  which  is  used  in  medicine,  is 
obtained  by  dissolving  the  hydrated  sesquioxide  of  iron  in 
dilute  hydrochloric  acid.  When  greatly  concentrated,  the 
solution  of  sesquichloride  of  iron  yields,  sometimes  orange- 
yellow  crystalline  needles,  radiating  from  a  centre,  which  are 
FcjClg  +  12H0,  at  other  times,  large  dark  yellowish-red 
crystals,  Ye^  CI3  +  5H0.  Mixed  with  sal-ammoniac,  and 
evaporated  in  vacuo,  it  affords  beautiful  ruby-red  octohedral.^ 
crystals,  consisting  of  2  eq.  of  chloride  of  ammonium,  and 
1  eq.  sesquichloride  of  iron,  with  2  eq.  of  water,  Fcj  CI3. 
2NH4  CI  I-  2H0.  Of  this  water,  the  double  salt  loses  1 
eq.  at  150°,  and  the  other  when  dried  above  300°  (Graham). 
There  is  a  similar  double  salt,  containing  chloride  of  potassium, 
but  not  so  easily  formed.  Sesquichloride  of  iron  is  soluble 
both  in  alcohol  and  ether.  A  strong  aqueous  solution  was 
found  by  Mr.  R.  Phillips  to  dissolve  not  less  than  4  eq.  of 
freshly  precipitated  ferric  hydrate,  becoming  deep  red  and 
opaque. 

Sesqui-iodide  of  iron  is  formed  in  similar  circumstances  to 
the  preceding  sesquicliloride. 

Sesquicyanide  of  iron,  Ferric  cyanide,  Ye^Cj^,  is  unknown 
in  the  pure  state.  A  solution  of  it,  which  is  decomposed  by 
evaporation,  is  obtained  by  precipitating  the  potash  of  the  red 
prussiate  by  fluoride  of  silicon.  It  forms  a  numerous  class  of 
double  cyanides.  A  compound  of  the  two  cyanides  of  iron, 
like  the  compound  oxide,  is  obtained  as  a  green  powder,  when 
a  solution  of  the  yellow  prussiate  of  potash,  charged  with 
excess  of  chlorine,  is  heated  or  exposed  to  air.  The  precipitate 
should  be  boiled  with  eight  or  ten  times  its  weight  of  concen- 


FERRIC    COMPOUNDS.  49 

trated  hydrochloric  acid,  and  well  washed.  Its  formula  is, 
FeCy.  Fe2Cy3  +  4H0.* 

Hydroferricyanic  acid;  H3Fe2Cy6,  or  H3.(Cy3Fc)2,  or 
3HCy.Fe2Cy3,  is  obtained  by  decomposing  ferricyanide  of 
lead  with  sulphuric  or  hydrosulphuric  acid.  The  decanted 
yellow  solution  yields,  by  careful  evaporation,  brownish 
needles,  which  redden  litmus  strongly,  and  have  a  rough 
sour  taste.  This  solution  gives  a  deep  blue  precipitate 
(TumbulPs  blue),  with  ferrous  salts.  This  acid,  united  with 
salifiable  bases,  forms  the  ferricyanides  M3Fe2Cy6.  The 
potassium  salt  is  described  in  Vol.  I.  p.  530. 

Prussian  blue,  Fe^  •  3(Cy3Fe),  or  3FeCy.  2Fe2Cy3.  —  This  ' 
remarkable   substance  is  precipitated   whenever   the  yellow 
prussiate  of  potash  is  added  to  a  sesquisalt  of  iron.     Thus 
with  the  sesquichloride : 

3K2FeCy3  +  2Fe2Cl3"=  Fe4.3(Cy3Fe)  +  6KCI3. 

Care  must  be  taken  to  avoid  an  excess  of  the  yellow  prussiate, 
as  the  precipitate  is  apt  to  carry  down  a  portion  of  that  salt. 
The  precipitate  also  contains  water  which  cannot  be  separated 
from  it  without  decomposition.  On  the  large  scale,  prussian 
blue  is  sometimes  prepared  by  precipitating  green  vitriol  with 
yellow  prussiate  of  potash,  and  subjecting  the  white  precipi- 
tate, KFe2Cy3,  to  the  action  of  oxidising  agents,  such  as 
chlorine  or  nitric  acid.  This  process,  however,  is  likely  to 
yield  ferricyanide  of  iron  and  potassium,  KFe4Cy6  (p.  40.), 
rather  than  prussian  blue,  properly  so  called. 

Prussian  blue,  dried  at  the  temperature  of  the  air,  is  a  light 
porous  body,  of  a  rich  velvety  blue  colour ;  dried  at  a  higher 
temperature  it  is  more  compact,  and  exhibits  in  mass  a  cop- 
pery lustre.  It  is  tasteless,  and  not  poisonous.  Alkalies  de- 
compose it,  precipitating  sesquioxide  of  iron  and  reproducing 
an  alkaline  ferrocyanide.  This  renders  prussian  blue  of  little 
value  in  dyeing,  as  it  is  injured  by  washing  with  soap.     Ked 

*  Pelouze,  Ann.  Ch.  Phys.  [2],  Ixix.  40. 
VOL.  II.  E 


50  IRON. 

oxide  of  mercury  boiled  with  prussian  blue,  affords  the  soluble 
cyanide  of  mercury,  with  an  insoluble  mixture  of  oxide  and 
cyanide  of  iron.  Prussian  blue  is  destroyed  by  fuming  nitric 
acid,  but  combines  with  oil  of  vitriol,  forming  a  white  pasty 
mass,  which  is  decomposed  by  water. 

The  combination  of  prussian  bhic  and  sesquioxide  of  iron, 
called  basic  prussian  blue^  was  noticed  at  page  40. 

Although  there  is  no  carbonate  of  the  sesquioxide  of  iron, 
the  hydrated  sesquioxide  is  dissolved  by  alkaline  bicai'bonates, 
under  certain  conditions  which  are  not  well  understood,  and 
d  red  solution  is  formed. 

Ferric  sulphates.  —  The  neutral  sulphate,  Fe203.  SSOg,  is 
formed  by  adding  to  a  solution  of  the  protosulphate,  half  as 
much  sulphuric  acid  as  it  already  contains,  and  oxidising  by 
nitric  acid.  It  gives  a  syrupy  liquid,  without  crystallising. 
This  salt  is  found  native  in  Chili,  forming  a  bed  of  consider- 
able thickness.  It  is  generally  massive,  but  forms  also  six- 
sided  prisms,  with  right  summits,  which  are  colourless,  and 
contain  OHO  (Rose).  Ferric  sulphate  is  soluble  in  alcohol. 
It  may  be  rendered  anhydrous  by  a  low  red  heat ;  but  after 
ignition,  it  dissolves  in  water  with  extreme  slowness,  like 
calcined  alum. 

When  hydrated  ferric  oxide  is  digested  in  the  neutral  sul- 
phate, a  red  solution  is  formed,  which,  according  to  Maus,  is 
the  compound  FcjOg.  2SO3.  The  rusty  precipitate  which  is 
formed  in  a  solution  of  the  protosulphate  from  absorption  of 
oxygen,  is  another  subsulphate,  of  which  the  empirical  formula 
is  2Fe203.  SO3.  The  decomposition  may  be  represented  by 
the  following  equation: — 

lOlFeO.SOg)  +  50  =  2Fe203.S03  +  SlFcaOg-SSOa). 

The  neutral  ferric  sulphate  remains  in  solution. 

A  potassio-ferric  sulphate,  or  iron  alum,  is  formed  by  eva- 
poratmg  a  solution  of  the  mixed  salts  to  their  point  of  crystal- 


FERRIC    SULPHATES.  51 

lisation.  It  is  colourless  and  exactly  analogous  in  composition 
to  ordinary  alum  (I.  606.).  Its  formula  is  KO  •  SO3  +  ¥efiy 
3SO3  +  24HO. 

Another  double  sulphate  is  formed,  which  crystallises 
in  large  six-sided  tables,  and  of  which  the  formula  is 
2(K0  •  SO^j  +  FcaOg  •  2SO3  +  6HO  (Maus),  when  potash  is 
added  gradually  to  a  concentrated  solution  of  ferric  sulphate, 
till  the  precipitate  formed  ceases  to  redissolve,  and  the  solu- 
tion is  evaporated  in  vacuo. 

Berzelius  designates  as  ferroso-ferric  sulphate  a  combination 
containing  FeO  *  S03  +  re203  •  3SO3.  It  is  the  salt  produced 
when  a  solution  of  the  neutral  protosulphate  of  iron  is  ex- 
posed to  the  air,  till  no  more  ochre  is  precipitated.  The 
solution,  which  is  yellowish  red,  does  not  crystallise,  but  gives 
the  black  oxide  of  iron  when  precipitated  by  an  alkali.  A 
salt  of  the  same  constituents,  but  in  different  proportions, 
forms  large  stalactites,  composed  of  little  transparent  crys- 
tals, in  the  copper  mine  of  Fahlun.  This  last  is  represented 
by  SFeO  •  2S03  4-3(Fe203  •  2S03)-h36HO  (Berzelius). 

Ferric  nitrate.  —  By  dissolving  iron  in  nitric  acid,  without 
heat,  as  in  Schoenbein^s  experiments  (page  35),  a  salt  is  ob- 
tained in  large,  transparent,  colourless  crystals.  From  more 
than  one  analysis,  Pelouze  found  the  constituents  of  this 
salt  to  be  in  the  proportion  of  2Fe203.3N05 +  1^110.  Its 
solution  is  decomposed  by  heat,  with  deposition  of  ferric  oxide. 
Ordway*,  by  digesting  metallic  iron  in  nitric  acid  of  sp. 
gr.  1'20,  obtained,  first  a  greenish  solution,  then  a  red,  and 
ultimately  a  rusty  brown  precipitate ;  and  on  adding  an  equal 
volume  of  nitric  acid  of  sp.  gr.  1*43  as  soon  as  the  last  pre- 
cipitate began  to  form,  and  cooling  the  liquid  below  60°, — or 
by  evaporating  the  greenish  solution,  adding  a  large  excess  of 
nitric  acid  and  cooling, —  colourless,  oblique,  rhombic  prisms, 
were    formed    containing    Fe203  •  3  NO5  +  18  HO ;    they 


*  Sm.  Am.  J.  [2],  k.  30. 
B  2 


53  IRON. 

were  deliquescent,  sparingly  soluble  in  nitric  acid,  melted  at 
about  116°  to  a  red  liquid,  and  gave  off  their  acid  partly  at 
212^,  completely  at  a  red  beat.  Two  ounces  of  these  crystals 
pounded  and  mixed  with  an  equal  weight  of  pulverised 
bicarbonate  of  ammonia,  produced  a  fall  of  temperature 
from  +58°  to  —5°.  By  adding  this  compound  to  recently 
precipitated  ferric  hydrate,  Ordway  obtained  basic  salts  con- 
taining from  1  to  8  eq.  oxide  to  1  eq.  acid.  The  solutions  of 
these  salts  were  of  a  deep  red  colour ;  were  not  decomposed 
by  boiling  or  dilution;  but  when  they  contained  a  large 
excess  of  oxide,  were  decomposed  by  the  addition  of  chloride 
of  sodium  and  other  salts.  Hausmann*,  by  evaporating  the 
solution  of  iron  in  nitric  acid  to  a  syrup,  adding  half  the 
volume  of  strong  nitric  acid,  and  leaving  the  solution  to 
crystallise,  obtained  colourless  prisms  containing  FcaOg. 
3  NO5  +  12  HO.  By  mixing  a  very  concentrated  solution 
of  this  neutral  salt  with  water  till  the  colour  became 
reddish  yellow,  then  boiling,  and  adding  nitric  acid  after 
cooling,  an  ochre-coloured  precipitate  was  formed,  containing 
8  FcgOg  •  2  NO5  +  3  HO.  By  adding  a  very  large  quantity  of 
water  to  a  highly  concentrated  and  slightly  acid  solution  of 
the  nitrate,  an  ochre-coloured  precipitate  was  sometimes 
formed,  containing  36  Fe203.N05  +  48HO.  By  treating  iron 
in  excess  wath  nitric  acid,  a  precipitate  was  obtained  having 
the  composition  8Fe203.NO^  +  12H0. 

Ferric  oxalate  is  very  soluble  and  does  not  crystallise. 
It  forms  a  double  salt  with  oxalate  of  potash,  of  a  rich  green 
colour,  of  which  the  formula  is  3(KO.C203)  +  re203.3C203 
+  6H0.  The  crystals  effloresce  in  dry  air.  In  this 
double  salt,  the  ferric  oxide  may  be  replaced  by  alumina 
or  oxide  of  chromium.  This  salt  is  formed  by  dissolving 
hydrated  ferric  oxide  to  saturation  in  bioxalate  of  potash 
(salt  of  sorrel),  and  crystallises  readily  from  a  concentrated 

•  Ann.  Ch.  Pharm.  Ixxxix.  100. 


FERRIC    ACID.  ^  53 

Solution.  The  circumstance  of  its  being  the  salt  of  sesqui- 
oxide  of  iron  most  easily  obtained  and  preserved  in  a  dry  state 
should  recommend  it  as  a  pharmaceutical  preparation. 

The  henzoate  and  succinate  of  ferric  oxide  are  insoluble 
precipitates.  Hence  the  benzoate  and  succinate  of  ammonia 
are  employed  to  separate  iron  from  manganese.  As  both 
these  precipitates  are  dissolved  by  acids,  the  iron  solution 
should  be  made  as  neutral  as  possible.  The  formula  of  the 
succinate  is,  Fe203.S. 

Ferric  acid,  FeOg. — This  compound,  which  is  analogous 
to  manganic  acid,  is  obtained  in  the  form  of  a  potash-salt  by 
exposing  metallic  iron  or  ferric  oxide  to  the  action  of  powerful 
oxidising  agents.  1.  A  mixture  of  1  part  iron-filings  and 
2  parts  nitre  is  projected  into  a  capacious  crucible  kept  at  a 
dull  red  heat,  and  the  crucible  removed  from  the  fire  as  soon  as 
the  mixture  begins  to  deflagrate  and  form  a  white  cloud ;  if  the 
heat  is  too  strong,  the  compound  decomposes  as  fast  as  it  is 
formed.  The  soft,  somewhat  friable  mass  of  ferrate  of  potash 
thus  obtained,  may  be  taken  out  with  an  iron  spoon,  and 
preserved  in  well  stoppered  bottles ;  or  the  ferrate  of  potash 
may  be  obtained  in  solution  by  treating  the  fused  mass  with 
ice-cold  water,  leaving  the  liquid  to  stand  to  allow  the  un- 
dissolved ferric  oxide  to  settle  down,  and  then  decanting ;  the 
solution  must  not  be  filtered,  as  it  is  immediately  decomposed 
by  contact  with  organic  matter.  2.  Ferrate  of  potash  is  also 
formed  by  igniting  ferric  oxide  with  hydrate  of  potash  in  an 
open  crucible,  or  with  a  mixture  of  hydrate  of  potash  and 
nitre.  3.  Chlorine  gas  is  passed  through  a  very  strong  solu- 
tion of  caustic  pctash  containing  hydrated  ferric  oxide  in 
suspension,  fragments  of  solid  potash  being  continually 
added  in  order  to  maintain  a  large  excess  of  alkali  in  the 
liquid.  The  ferrate  of  potash,  being  almost  insoluble  in  the 
strong  alkaline  liquid,  is  deposited  in  the  form  of  a  black 
powder,  which  may  be  freed  from  the  greater  part  of  the 
mother -liquor  by  drying  it  on  a  plate  of  porous  earthenware. 

E  3 


54  IRON. 

Ferrate  of  potash  is  a  very  unstable  compound,  and  has  not 
been  obtained  in  the  crystalline  form.  Its  solution  is  of  a 
deep  red  colour,  like  that  of  permanganate  of  potash.  The 
acid  has  not  been  obtained  in  the  free  state ;  it  appears  in- 
deed to  be  scarcely  capable  of  existing  in  that  state,  decom- 
posing, as  soon  as  liberated,  into  oxygen  and  ferric  oxide. 
Ferrate  of  baryta  is  formed  by  adding  a  solution  of  ferrate  of 
potash  to  a  dilute  solution  of  a  baryta-salt;  it  then  fails 
down  as  a  deep  carmine-coloured  precipitate,  which  may  be 
washed  and  dried  without  changing  colour.  It  gives  off 
oxygen  when  heated,  and  is  readily  decomposed  by  acids. 

Nitroprussic  acid;  Fe2Cy5(N02).H2.  This  acid  and  its 
salts  were  discovered  by  Dr.  Lyon  Playfair.*  It  is  formed  by 
the  action  of  nitric  acid  (or  rather  of  nitric  oxide)  on  hydro- 
ferrocyanic  acid  or  a  ferrocyanide.  The  hydroferrocyanic 
acid  is  first  converted  into  hydroferricyanic  acid  : 

4H2reCy3  +  NO2  =  2H3Fe2Cy6  +  2H0  +  N ; 

and  afterwards,  by  the  further  action  of  the  nitric  oxide,  into 
nitroprussic  acid : 

HjFejCye  +  NO,  =  Pe,Cy,(NO,).H^  +  HCy. 

Cyanogen  is  also  evolved  and  oxamide  deposited ;  but  these 
products  are  due  to  a  secondary  action. 

To  prepare  the  potassium  or  sodium  salt,  ferrocyanide  of 
potassium  (2  eq.)  is  digested  in  the  cold  with  ordinaiy  nitric 
acid  (5  eq.)  diluted  with  an  equal  bulk  of  water,  till  it  is 
completely  dissolved ;  the  solution  boiled  till  it  forms  with 
ferrous  salts  no  longer  a  dark  blue,  but  a  green  or  slate- 
coloured  precipitate,  and  then  left  to  crystaUise,  where- 
upon it  deposits  a  large  quantity  of  nitre,  together  with 
oxamide.  The  strongly  coloured  mother-liquor  is  neutralised 
with  carbonate  of  potash  or  soda ;  boiled ;  filtered  to  separate 

*  Phil.  Trans.  1849,  ii.  477. 


NITROPRUSSIC   ACID.  55 

a  green  or  brown  precipitate ;  and  again  left  to  crystallise. 
Nitrate  of  potash  or  soda  then  crystallises  out  first;  and 
afterwards,  by  further  evaporation,  the  nitroprussiate.  The 
sodium-salt  crystallises  most  readily,  forming  large  ruby- 
coloured  prisms,  which  dissolve  in  2i  parts  of  water  at  60°, 
and  in  a  smaller  quantity  of  hot  water.  From  the  solution 
of  this  salt,  the  silver-salt  may  be  obtained  by  double  decom- 
position j  and  this,  when  decomposed  by  hydrochloric  acid, 
yields  nitroprussic  acid.  This  acid  crystallises  in  dark  red, 
very  deliquescent,  oblique  prisms,  which  dissolve  very  readily 
in  water,  alcohol,  and  ether.  The  aqueous  solution  is  very 
prone  to  decomposition. 

The  general  formula  of  the  nitroprussiates  or  nitroprussides 
is  FcgCyg  (N02).M2*  :  the  radical  (which  might  be  called  nitro- 
ferro cyanogen)  may  be  regarded  as  2  eq.  of  ferrocyanogen, 
or  1  eq.  of  ferricyanogen,  Fe2Cy6,  in  which  1  eq.  of  cyanogen 
is  replaced  by  nitric  oxide,  NO2.  Most  of  them  are  strongly 
coloured;  the  ammonium,  potassium,  sodium,  barium,  stron- 
tium, calcium,  and  lead  salts,  dissolve  readily  in  water, 
forming  deep  red  solutions  from  which  the  salts  are  not 
precipitated  by  alcohol.  The  other  nitroprussiates  are  inso- 
luble, or  sparingly  soluble.  A  solution  of  a  nitroprussiate 
forms,  with  the  solution  of  an  alkaline  sulphide,  a  splendid 
blue  or  purple  colour,  which  affords  an  extremely  delicate 
test  of  the  presence,  either  of  a  nitroprussiate,  or  of  an 
alkaline  sulphide. 


*  This  formula  was  proposed  by  Gerhardt.  Playfair  originally  gave  the 
formula  EegCyi2(NO)3.Mg  ;  and  subsequently  {P//il.  Mag.  [3.]  xxxvi.  360) 
suggested  the  simpler  formula,  Fe2Cy3(NO)  .M2.  G-erhardt's  formula,  however, 
agrees  quite  as  well  with  the  analyses  of  the  best  defined  nitroprussiates  as 
either  of  these,  and  is  more  in  accordance  with  certain  reactions;  viz.,  that 
nitroprussiate  of  sodium,  exposed  to  sunshine,  actually  gives  off  nitric  oxide  j 
and  that  when  a  solution  of  the  barium-salt  is  treated  with  red  oxide  of  mer- 
cury, part  of  the  nitrogen  is  converted  into  nitric  acid. 


£  4 


56  IRON. 


QUANTITATIVE    ESTIMATION    OF    IRON. 

Iron  is  always  estimated  in  the  form  of  sesquioxide.  If 
the  solution  contains  protoxide,  either  alone  or  mixed  with 
sesquioxide,  it  is  first  boiled  mth  a  sufficient  quantity  of 
nitric  acid  to  convert  the  whole  of  the  protoxide  into 
sesquioxide,  and  then  treated  with  ammonia  in  excess  to 
precipitate  the  latter.  The  precipitate  is  collected  on  a 
filter,  washed,  dried,  and  ignited  at  a  moderate  red  heat; 
too  high  a  temperature  expels  a  portion  of  the  oxygen. 
Every  10  parts  of  pure  sesquioxide  correspond  to  7  parts 
of  metallic  iron.  In  some  cases,  however,  it  is  necessary  to 
use  potash  as  the  precipitant.  In  that  case,  the  precipitated 
ferric  oxide  is  very  apt  to  carry  down  with  it  a  portion 
of  the  potash,  which  is  exceedingly  difficult  to  remove  by 
washing.  It  is  best  therefore,  after  having  washed  it  two 
or  three  times  with  hot  w^ater,  to  re-dissolve  it  in  acid  and 
precipitate  by  ammonia.  In  other  cases,  as  when  the  solu- 
tion contains  organic  matter,  the  iron  must  be  precipitated 
by  sulphide  of  ammonium,  because  such  substances  prevent 
the  precipitation  of  the  oxide.  The  precipitated  sulphide, 
after  being  washed,  is  then  dissolved  in  nitric  acid,  and  the 
iron  precipitated  by  ammonia  as  before. 

Volumetric  method. — The  quantity  of  iron  in  a  solution 
may  also  be  estimated  by  reducing  it  aU  to  the  state  of 
protoxide,  either  by  sulphurous  acid  or  by  metallic  zinc  (in 
the  former  case  the  excess  of  sulphurous  acid  must  be  ex- 
pelled by  boiling),  and  then  adding,  from  a  graduated  burette, 
a  quantity  of  solution  of  permanganate  of  potash,  sufficient 
to  convert  all  the  protoxide  of  iron  into  sesquioxide : 

KO  •  MusOy  +  10FeO=  2MnO  +  KO  -VhY^jdy 

The  liquid  must  contain  an  excess  of  acid,  to  hold  the  oxide 
of  manganese  in  solution.     The  first  portions  of  perman- 


QUANTITATIVE    ESTIMATION    OP    IRON.  57 

ganate  added  produce  no  visible  effect ;  but  as  soon  as  all  the 
protoxide  of  iron  is  converted  into  sesquioxide,  the  addition 
of  another  drop  of  the  permanganate  imparts  a  rose  tint  to 
the  liquid.  The  value  of  the  solution  of  the  permanganate 
must  be  previously  ascertained  by  dissolving  1  gramme  of 
iron  (harpsichord  wire)  in  hydrochloric  acid,  and  determin- 
ing the  number  of  divisions  of  the  burette  occupied  by  the 
quantity  of  the  solution  required  to  convert  that  quantity  of 
iron  into  sesquioxide.  (Margueritte,  Ann.  Ch.  Phys.  [3], 
18,244.) 

The  preceding  method  may  also  be  applied  to  determine 
the  quantities  of  protoxide  and  sesquioxide  of  iron  in  a  solu- 
tion when  they  occur  together, — viz.,  by  first  treating  a 
portion  of  the  solution,  as  it  is,  in  the  manner  just  described ; 
then  taking  another  equal  portion,  reducing  all  the  iron  in 
it  to  protoxide  by  sulphurous  acid,  and  applying  the  same 
method  to  the  solution  thus  reduced.  The  first  determina- 
tion gives  the  quantity  of  iron  in  the  state  of  protoxide ;  the 
second,  the  total  quantity  present :  the  difference  is  therefore 
the  quantity  in  the  form  of  sesquioxide. 

Separation  of  iron  from  the  metals  previously  described. — 
From  the  alkalies  and  alkaline  earths,  iron  is  separated  by 
ammonia,  after  having  been  brought  to  the  state  of  sesqui- 
oxide. In  the  case  of  the  alkaline  earths,  care  must  be 
taken  to  add  but  a  slight  excess  of  ammonia,  to  filter  quickly, 
and  exclude  the  air  as  completely  as  possible  during  the 
filtration ;  otherwise  the  free  ammonia  will  absorb  carbonic 
acid  from  the  air,  and  then  throw  down  the  earths  in  the  form 
of  carbonates,  together  with  the  ferric  oxide.  Should  such 
precipitation  occur,  —  which  may  generally  be  known  by  the 
colour  of  the  oxide, — the  precipitate  must  be  re-dissolved 
and  the  treatment  with  ammonia  repeated.  If  the  solution 
contains  fixed  organic  substances,  such  as  sugar,  tartaric 
acid,  &c.,  the  iron  must  be  precipitated  by  sulphide  of  am- 


58  IRON. 

monium,  and  the  precipitate  treated  in  the  manner  already 
described  (p.  56.) 

From  alumina  and  glucina,  iron  is  separated  by  potash, 
which  precipitates  the  iron,  but  holds  the  alumina  or  glucina 
in  solution.  The  precipitate,  which  always  contains  potash, 
must  then  be  re-dissolved  in  acid,  and  the  iron  re-precipitated 
by  ammonia. 

The  separation  of  iron  from  zirconia,  yttriay  and  thorina, 
is  effected  by  adding  a  sufficient  quantity  of  tartaric  acid  to 
prevent  the  earths  from  being  precipitated  when  the  solution 
is  rendered  alkahne,  and  throwing  down  the  iron  by  sulphide 
of  ammonium. 

From  magnesia  and  from  manganous  oxide,  iron  is  most 
effectually  separated  by  succinate  or  benzoate  of  ammonia. 
The  solution,  after  all  the  iron  has  been  brought  to  the  state 
of  sesquioxide,  is  mixed  with  a  sufficient  quantity  of  sal- 
ammoniac  to  hold  the  magnesia  or  manganous  oxide  in  solu- 
tion, and  very  carefully  neutralised  with  ammonia;  it  is 
then  treated  with  benzoate  or  succinate  of  ammonia,  which 
throws  down  the  iron  as  ferric  benzoate  or  succinate, 
leaving  the  magnesia  or  manganous  oxide  in  solution.  The 
precipitate  is  washed  and  dried,  and  ignited  in  an  open 
platinum  crucible,  so  that  the  air  may  have  sufficient  access 
to  it  to  prevent  any  reduction  of  the  iron  by  the  carbon  of 
the  organic  acid.  Should  such  reduction  take  place,  the  iron 
must  be  re-oxidized  by  nitric  acid.  The  success  of  this  mode 
of  separation  depends  entirely  on  the  care  with  which  the 
acid  in  the  solution  is  neutralised  with  ammonia  before  add- 
ing the  benzoate  or  succinate.  If  too  much  ammonia  has 
been  added,  manganese  or  magnesia  goes  down  with  the  iron ; 
if  too  little,  a  portion  of  iron  remains  in  solution.  The 
addition  of  ammonia  should  be  continued  till  a  small  quan- 
tity of  ferric  oxide  is  precipitated,  and  does  not  re-dissolve  on 
agitation.  The  supernatant  liquid  has  then  a  deep  brown 
colour,  the  greater  part  of  the  iron  being  still  in  the  solution. 


COBALT.  59 

The  separation  of  ferric  oxide  from  manganous  oxide  may 
also  be  effected  by  agitating  the  solution  with  excess  of  car- 
bonate of  lime  or  baryta,  which  precipitates  the  iron  but  not 
the  manganese.  According  to  J.  Schiel*,  manganese  may 
be  separated  from  iron  by  mixing  the  solution  with  acetate 
of  soda  and  passing  chlorine  through  it ;  bioxide  of  manganese 
is  then  alone  precipitated.  The  methods  of  separation  given 
at  page  7.  serve  very  well  for  preparing  a  pure  salt  of  man- 
ganese from  a  solution  containing  that  metal  together  with 
iron,  but  are  not  adapted  for  quantitative  analysis. 


Aridium  ?  This  name  was  given  by  Ullgren  to  a  metal  which  he  be- 
lieved to  exist  in  the  chrome-iron  ores  of  Roros  in  Sweden,  and  in  the 
iron  ores  of  Oernstolso.  Its  characters  very  much  resemble  those  of  iron. 
It  forms  two  oxides  analogous  to  those  of  iron,  and  presenting,  both  with 
liquid  reagents  and  with  the  blowpipe,  characters  which  might  be  exliibited 
by  oxides  of  iron  containing  a  little  chromium  (vid.  Chem.  Gaz.  1854,  289} ; 
Bahr  {Ann.  Ch.  Fharm.  Ixxxvii.  264),  endeavoured  to  prepare  the  supposed 
new  metal  by  Ullgren's  process,  and  came  to  the  conclusion  that  it  was 
merely  iron  containing  a  little  phosphorus,  and  perhaps  also  chromium. 


SECTION    III. 

COBALT. 

%.  29-52,  07-369;  Co. 

Cobalt  occurs  in  the  mineral  kingdom  chiefly  in  combina- 
tion with  arsenic,  as  arsenical  cobalt,  CoAs ;  or  with  sulphur 
and  arsenic,  as  grey  cobalt  ore,  CoAs.CoSg,  but  contaminated 
with  iron,  nickel,  and  other  metals.  Its  name  is  that  of  the 
Kobolds  or  evil  spirits  of  mines,  and  was  applied  to  it  by  the 
•SeU.  Am.  J.  [2],  XV.  275. 


60  COBALT. 

superstitious  miners  of  the  middle  ages,  who  were  often  de- 
ceived by  the  favourable  appearance  of  its  ores.  These  remained 
without  value,  till  the  middle  of  the  sixteenth  century,  when 
they  were  first  applied  to  colour  glass  blue.  They  are  now 
consumed  in  great  quantity  for  the  blue  colours  of  porcelain 
and  stoneware.  Cobalt  is  likewise  found  in  almost  all  meteoric 
stones. 

To  obtain  metallic  cobalt,  the  native  arsenide  is  repeatedly 
roasted,  by  which  the  greater  part  of  the  arsenic  is  converted 
into  arsenious  acid,  and  carried  off  in  vapour,  while  the  impure 
oxide  of  cobalt,  known  as  zaffre,  remains.  This  is  dissolved 
in  hydrochloric  Jicid,  and  the  remaining  arsenic  precipitated 
as  sulphide,  by  passing  a  stream  of  sulphuretted  hydrogen 
through  the  solution.  To  get  rid  of  the  iron  present,  the  last 
solution,  after  filtration,  is  boiled  with  a  little  nitric  acid,  to 
peroxidise  that  metal ;  and  carbonate  of  potash  is  added  in 
excess,  which  throws  down  carbonate  of  cobalt  and  sesquioxide 
of  iron.  The  precipitate  is  treated  with  oxalic  acid,  which 
forms  an  insoluble  oxalate  of  cobalt  and  soluble  ferric  oxalate. 
The  oxalate  of  cobalt  is  dried  and  decomposed  by  ignition  in 
a  covered  crucible,  when  the  oxide  is  reduced  by  the  carbon 
of  the  acid,  which  goes  off  as  carbonic  acid,  while  the  metallic 
cobalt  remains  as  a  black  powder.  To  separate  cobalt  from 
nickel,  with  which  it  is  almost  always  associated,  the  mixed 
oxalates  of  cobalt  and  nickel,  obtained  by  the  preceding  pro- 
cess, are  dissolved  in  ammonia,  after  which  the  liquid  is  diluted 
and  exposed  to  the  air  in  a  shallow  basin  for  several  days.  The 
ammonia  evaporates,  and  the  salt  of  nickel  precipitates  as  a 
green  powder,  while  the  salt  of  cobalt  remains  in  solution. 
The  liquid  is  then  decanted,  and  if  no  additional  precipitate 
subsides  from  it  in  twenty-four  hours,  it  is  free  from  nickel, 
and  may  be  evaporated  to.  dryness.  The  precipitate  of  nickel 
contains  a  little  cobalt.* 

Cobalt  is  a  brittle  metal,  of  a  reddish  grey  colour,  some- 
*  For  other  methods  of  separating  nickel  and  cobalt,  see  Nickel. 


SALTS    OF    COBALT.  61 

what  more- fusible  than  iron,  and  of  the  density  8'5131 
(Berzelius).  Rammelsberg,  in  five  experiments  with  cobalt 
reduced  by  hydrogen,  found  the  specific  gravity  to  vary  from 
8-132  to  9-495 ;  the  mean  is  8-957.  Pure  cobalt  is  mag- 
netic, but  a  minute  quantity  of  arsenic  causes  it  to  lose  that 
property. 

Cobalt  is  less  oxidable  in  the  air  or  by  acids  than  iron,  dis- 
solving slowly  in  diluted  hydrochloric  or  sulphuric  acid,  when 
heated,  with  evolution  of  hydrogen ;  but  it  is  readily  oxidised 
by  nitric  acid.  This  metal  forms  a  protoxide  and  sesqui- 
oxide,  CoO  and  C02O3,  corresponding  with  the  oxides  of 
iron,  and  three  intermediate  oxides,  viz.,  €0304  =  000.00203; 
0o6O7  =  40oO.0o2O3;  and  0o8O9=60oO.0o2O3.  According 
to  Fremy,  the  first  of  these,  viz.,  O03O4  is  a  salifiable  base  com- 
bining directly  with  acetic  acid,  and  existing  in  several  am- 
monio-salts  of  cobalt.  Fremy  has  also  obtained  compound  salts 
of  this  nature  containing  a  bioxide  of  cobalt  OoOg 

Protoxide  of  cobalt,  Cobaltous  oxide,  CoO,  37-52  or  469. — 
Prepared  by  the  ignition  of  the  carbonate.  This  oxide  is  a 
powder  of  an  ash-grey  colour.  It  colours  glass  blue,  even 
when  in  minute  quantity,  no  other  colouring  matter  having 
so  much  intensity.  Smalt  blue  is  a  pounded  potash-glass 
containing  cobalt.  All  compounds  of  cobalt,  when  heated 
with  borax  or  phosphorus -salt,  either  in  the  inner  or  in  the 
outer  blowpipe-flame,  impart  a  splendid  blue  colour  to  the 
bead.  This  coloration  afibrds  an  extremely  delicate  test  for 
cobalt. 

The  salts  of  protoxide  of  cobalt  have  a  reddish  colour  in 
solution.  Potash  or  soda  added  to  these  solutions  forms  a 
blue  precipitate  of  the  hydrated  oxide,  insoluble  in  excess  of 
the  reagent.  Ammonia  also  forms  a  blue  precipitate,  which 
dissolves  in  excess  of  ammonia,  yielding  a  red-brown  solution. 
If  the  cobalt  solution  contains  a  large  quantity  of  free  acid 
or  of  an  ammoniacal  salt,  no  precipitate  is  formed  by  ammonia. 
Alkaline  carbonates  precipitate  a  pink  carbonate  of  cobalt. 


62  COBALT. 

soluble  in  carbonate  of  ammonia.  Hydromlphuric  add  does 
not  precipitate  a  solution  of  cobalt  xjontaining  either  of  the 
stronger  acids ;  but  in  a  solution  of  acetate  of  cobalt,  or  of 
any  cobalt- salt  mixed  with  acetate  of  ammonia,  it  forms  a 
black  precipitate  of  protosulphide  of  cobalt.  Alkaline  ml- 
pJiides  throw  down  the  same  precipitate  from  all  solutions  of 
protoxide  of  cobalt. 

Oxide  of  cobalt  appears  to  combine  with  alkalies  and  earths 
as  well  as  with  acids.  It  dissolves  in  fused  potash,  and  imparts 
a  blue  colour  to  the  compound.  IMagnesia  mixed  with  a  drop 
of  nitrate  of  cobalt,  and  then  dried  and  ignited,  assumes  a 
feeble  but  characteristic  rose  tint.  A  compound  of  oxide  of 
cobalt  with  alumina  is  obtained  by  mixing  the  solution  of  a 
salt  of  cobalt,  which  must  be  perfectly  free  from  iron  or  nickel, 
with  a  solution  of  equally  pure  alum,  precipitating  the  liquor 
by  an  alkaline  carbonate,  washing  the  precipitate  with  care, 
then  drying  and  igniting  it  strongly.  It  forms  a  beautiful  blue 
pigment,  known  as  cobalt-blue,  which  may  be  compared  in 
purity  of  tint  with  ultramarine.  A  compound  of  oxide  of 
cobalt  with  oxide  of  zinc  of  a  fine  green  colour  may  be  prepared 
in  a  similar  manner.  These  coloured  compounds  often  aftbrd 
useful  confirmatory  tests  of  the  presence  of  zinc,  alumina,  or 
magnesia.  The  substance  to  be  examined  is  placed  on  pla- 
tinum foil,  moistened  with  nitrate  of  cobalt,  then  dried,  and 
strongly  heated  in  the  blo^vpipe-flame. 

Chloride  of  cobalt,  Co  CI,  is  obtained  by  dissolving  zaffre  or 
the  oxide  in  hydrochloric  acid.  Its  solution  is  pink-red,  and 
affords  hydrated  ciystals  of  the  same  colour ;  but  when  highly 
concentrated,  assumes  an  intense  blue  colour,  and  then  affords 
blue  crystals  of  chloride  of  cobalt,  which  are  anhydrous 
(Proust).  The  red  solution  is  used  as  a  sympathetic  ink; 
characters  written  with  it  on  paper  are  colourless  and  invisible, 
or  nearly  so,  but  when  the  paper  is  warmed  by  holding  it  near 
a  fire  or  against  a  stove,  the  writing  becomes  visible  and 
appears  of  a  beautiful  blue.     After  a  while,  as  the  salt  absorbs 


SALTS    OF    COBALT.  63 

moisture,  the  colour  again  disappears,  but  may  be  reproduced 
by  the  action  of  heat.  If  the  paper  be  exposed  to  too  high  a 
temperature,  the  writing  becomes  black,  and  does  not  after- 
wards disappear.  The  addition  of  a  salt  of  nickel  to  the  sym- 
pathetic ink  gives  a  green  instead  of  blue. 

The  neutral  carbonate  of  cobalt  is  unknown,  oxide  of  cobalt, 
like  magnesia,  being  thrown  down  from  its  solutions  by  alka- 
line carbonates,  as  a  carbonate  with  excess  of  oxide.  The  sub- 
carbonate  of  cobalt  is  a  pale  red  powder,  which  contains, 
according  to  Setterberger,  2  eq.  of  carbonic  acid,  5  eq.  of 
oxide  of  cobalt,  and  4  eq.  of  water. 

Besides  the  sulphate  of  cobalt  corresponding  with  green 
vitriol,  another  salt  was  crystallised  by  Mitscherlich  between 
68**  and  86°,  containing  6  eq.  of  water,  C0O.SO34-6HO,  iso- 
morphous  with  a  corresponding  sulphate  of  magnesia.  Sulphate 
of  cobalt  forms  the  usual  double  salts  with  the  sulphates  of 
potash  and  ammonia,  containing  6H0. 

Nitrate  of  cobalt,  C0O.NO5 — is  obtained  by  dissolving  the 
metal,  the  protoxide,  or  the  carbonate  in  dilute  nitric  acid. 
Its  solution  is  carmine -coloured,  and  on  evaporation  yields 
red  crystals  containing  6  eq.  of  water ;  they  deliquesce  in  the 
air,  fuse  below  100°,  and  at  a  higher  temperature  give  off 
water  and  melt  into  a  violet-red  liquid,  which  afterwards 
becomes  green  and  thick,  and  is  ultimately  converted,  with 
violent  intumescence  and  evolution  of  nitrous  fumes,  into  black 
sesquioxide  of  cobalt.  Characters  written  on  paper  with  a  solu- 
tion of  this  salt  assume  a  peach-blossom  colour  when  heated. 

A  seocbasic  nitrate,  6CoO.NOg  +  5Aq.,  is  obtained  on  adding 
excess  of  ammonia  to  a  well  boiled  solution  of  the  neutral 
nitrate,  carefully  protected  from  the  air.  It  then  falls  down 
as  a  blue  precipitate,  but  on  the  slightest  access  of  air  quickly 
assumes  a  grass-green  colour  and  partly  redissolves  in  the 
liquid. 

Cobalt-yellow,  CoO.KO.N208.--This  compound  is  formed 
by  adding  a  solution  of  nitrite  of  potash  (obtained  by  passing 


64 


COBALT. 


the  nitrous  fumes  evolved  from  a  heated  mixture  of  nitric  acid 
and  starch  into  caustic  potash)  to  an  acid  solution  of  nitrate 
of  cobalt ;  nitric  oxide  and  nitrate  of  potash  are  then  formed, 
and  the  cobalt-compound  separates  in  the  form  of  a  beautiful 
yellow  crystalline  powder : 

C0O.NO5  +  2NO5  -h  4(KO.N03)  =  3(KO.N05)  +  2NO2  + 
N2O8.C0O.KO. 

It  is  likewise  obtained  by  adding  potash,  not  in  excess,  to 
solution  of  nitrate  of  cobalt,  so  as  to  precipitate  a  blue  basic 
salt,  treating  this  with  a  slight  excess  of  nitrite  of  potash,  and 
adding  nitric  acid  in  a  thin  stream,  by  means  of  a  pipette. 
Also  by  treating  nitrate  of  cobalt  with  a  slight  excess  of 
potash,  so  as  to  throw  do^vn  the  rose-coloured  hydrated  oxide, 
and  passing  nitric  oxide  gas  into  the  mixture.  This  last  reac- 
tion is  so  rapid  that  it  may  be  exhibited  as  a  lecture-experi- 
ment. The  compound  crystallises  in  microscopic  four-sided 
prisms  with  pyramidal  summits.  It  is  insoluble  in  cold 
water,  also  in  alcohol  and  ether,  but  when  boiled  with  water 
gradually  dissolves  with  evolution  of  acid  vapours ;  the  solu- 
tion yields  on  evaporation  a  lemon-yellow  salt  of  different 
composition.  Nitric  acid  and  hydrochloric  acid  do  not  act 
upon  it  in  the  cold,  but  decompose  it  at  a  boiling  heat,  with 
evolution  of  nitrous  fumes.  Hydrosulphuric  acid  decom- 
poses it  very  slowly,  sulphide  of  ammonium  immediately, 
forming  black  sulphide  of  cobalt.  When  heated,  it  assumes 
an  orange-yellow  colour,  gives  off  water  and  aftei'wards  fumes 
of  nitric  and  hyponitric  acids,  and  leaves  sesquioxide  of  cobalt 
mixed  with  nitrite  of  potash.  Its  beautiful  colour,  its  perma- 
nence, and  the  facility  with  which  it  mixes  with  other  colours, 
render  it  well  adapted  for  artistic  purposes.* 

According  to  A.  Stromeyerf,  this  salt  is  a  nitrite  of  co- 


*  St.  Evre,  Ann.  Ch.  Phys.  [3],  xxxviii.  177. 
t  Ann.  Ch.  Pharm.  xcvi.  218. 


SALTS    OF    COBALT.  65 

baltic  oxide  and  potash,  Co203.2N03  +  3(KO.N03),  and  its 
formation  may  be  represented  by  the  equation, 

2(CoO.S03)  +  5(KO.N03)  +  0=  [Co203.2N03  4-3(KO.N03)] 
+  2(KO.S03). 

When  a  solution  of  lead  is  mixed  with  nitrite  of  potash  and 
acetic  acid,  the  liquid  assumes  a  yellow  colour,  but  no  precipi- 
tation takes  place ;  but  on  adding  a  cobalt-salt,  a  yellowish 
green  precipitate  (or  brownish  black  and  crystalline  from  dilute 
solutions)  is  formed,  whose  composition  is  that  of  the  yellow 
cobalt-compound  with  half  the  potash  replaced  by  oxide  of 
lead  (Stromeyer). 

Phosphate  of  cobalt ,  2CoO.HO.PO5,  is  an  insoluble  preci- 
pitate of  a  deep  violet  colour.  When  2  parts  of  this  phosphate 
or  1  part  of  the  arseniate  of  cobalt  are  carefully  mixed  with 
16  parts  of  alumina  and  strongly  ignited  for  a  considerable 
time,  a  beautiful  blue  pigment  is  obtained,  resembling  ultra- 
marine ;  it  was  discovered  by  Thenard. 

Arseniate  of  cobalt,  SCoO.AsOg  +  8H0,  exists  as  a  crystal- 
line mineral  called  cobalt-bloom. 

Sesquioxide  of  cobalt ,  Cobaltic  oooide,  C02O3,  is  formed  when 
chlorine  is  transmitted  through  water  in  which  the  hydrated 
protoxide  is  suspended,  or  when  a  salt  of  the  protoxide  is  precipi- 
tated by  a  solution  of  chloride  of  lime.  In  the  former  case,  water 
is  decomposed  by  the  chlorine,  and  hydrochloric  acid  produced, 
while  the  oxygen  of  the  water  peroxidises  the  cobalt ; 

2CoO  +  HO  +  CI  =  C02O3  +  HCl. 

The  sesquioxide  of  cobalt  is  precipitated  as  a  black  hydrate, 
containing  2H0.  This  hydrate,  when  cautiously  heated  tt 
600°  or  700°,  yields  the  black  anhydrous  oxide.  When  sesqui- 
oxide of  cobalt  is  digested  in  hydrochloric  acid,  clilorine  is 
evolved,  and  the  protochloride  formed.  Exposed  to  a  low 
red  heat,  the  sesquioxide  loses  oxygen,  and  the  compound 
oxide,  C0O.C02O3,  is  produced.  (Hess.)  When  protoxide  of 
VOL.  II.  r 


66  COBALT. 

cobalt  is  calcined  with  a  borax  glass,  at  a  moderate  heat^  it 
absorbs  oxygen,  and  a  black  mass  is  obtained,  which  mixed  with 
manganic  oxide,  serves  as  a  black  colour  in  enamel  painting. 

Sesquioxide  of  cobalt  acts  as  a  weak  base.  Phosphoric,  sul- 
phuric, nitric,  and  hydrochloric  acids  dissolve  its  hydrate  in 
the  cold,  without  decomposition  at  first,  but  the  resulting  salts 
are  afterwards  reduced  to  salts  of  the  protoxide.  A  protosalt 
of  cobalt  containing  a  small  quantity  of  a  sesquisalt  is  some- 
what deepened  in  coloiu*.  The  most  permanent  of  the  sesqui- 
salts  is  the  acetate ;  the  hydrated  sesquioxide  while  yet  moist 
dissolves  in  acetic  acid,  slowly  but  completely.  The  solution, 
which  has  an  intense  brown  colour,  forms  a  brown  precipitate 
with  alkalies  and  alkaline  carbonates.  With  ferrocyanide  of 
potassium  it  forms  a  dark  precipitate,  which,  if  the  precipitant 
is  in  excess,  gives  up  cyanogen  to  it,  converting  it  into  ferri- 
cyanide  of  potassium  and  being  itself  converted  into  green 
ferrocyanide  of  cobalt.  Alkaline  oxalates  colour  the  solution 
yellow,  forming  an  oxalate  of  the  oxide  C03O4. 

According  to  Fremy,  the  oxide  C03O4  combines  also  with 
other  acids.  The  acetate  of  this  oxide  is  obtained  by  digesting 
in  dilute  acetic  acid  the  hydrated  oxide  obtained  by  continued 
action  of  oxygen  on  the  blue  precipitate  tlirown  down  from 
ordinary  cobalt-salts  by  potash  not  in  excess.  Fremy  also 
states  that  when  chlorine  is  passed  into  the  solution  of  ordi- 
nary acetate  of  cobalt,  a  browTiish  yellow  salt  is  formed  con- 
taining the  base  CO3CIO3,  or  C03O4  in  which  1  eq.  of  O  is 
replaced  by  CI.  This  chlorine  base  exists  also  in  some  of  the 
amraonio  -compounds  of  cobalt  (pp.  68-72) .  The  oxide  C03OJ  is 
obtained  in  the  free  state  by  heating  the  nitrate  or  oxalate  of 
cobalt,  or  the  hydrated  sesquioxide  to  redness  in  contact  with 
the  air  (Hess,  Rammelsberg) ;  but  according  to  Beetz  and 
Winkclblech,  the  oxide  thus  obtained  is  CogO^.  When  the 
residue  obtained  by  gently  igniting  the  oxalate  in  contact 
with  the  air  is  digested  in  strong  boiling  hydrochloric  acid, 
the  oxide  C03O4  remains  in  liard,  brittle,  greyish-black  micro- 


SALTS    OF    COBALT.  67 

scopic  octohedrons  having  a  metallic  lustre.  The  same  crys- 
talline compound  is  obtained  by  igniting  dry  protochloride 
of  cobalt,  alone  or  mixed  with  sal-ammoniac,  in  dry  air  or 
oxygen  gas  (Schwarzenberg). 

A  cobaltic  acidj  C03O5,  is  obtained  in  combination  with 
potash  by  strongly  igniting  the  oxide  C03O4,  or  the  protoxide, 
or  the  carbonate,  with  pure  hydrate  of  potash.  A  crystalline 
salt  is  then  formed  which,  when  dried  at  100°  C,  contains 
KO.3C03O5  +  3HO,  and  gives  of  1  eq.  of  water  at  130° 
(Schwarzenberg) . 

Bioxide  of  cobalt,  C0O2J  has  not  been  obtained  in  the  free 
state,  but  exists  according  to  Fremy  in  the  oxycobaltiac  salts, 
(p.  68.) 

There  exist  three  sulphides  of  cobalt,  a  protosulphide,  sesqui- 
sulphide,  and  bisulphide. 

Sesquicyanide  of  cobalt  has  not  been  obtained  in  the  sepa- 
rate state,  but  it  exists  in  a  class  of  double  cyanidbs,  of  which 
the  radical  is  cobalticyanogen,  CygCo2,  analogous  to  ferri- 
cyanogen.  The  cobalticyanide  of  potassium,  corresponding 
with  the  red  prussiate  of  potash,  is  formed  when  protoxide  of 
cobalt  or  its  carbonate  is  dissolved  in  caustic  potash  which 
has  been  treated  with  an  excess  of  hydrocyanic  acid.  It  is 
an  anhydrous  salt,  pale  yellow  and  nearly  colourless  when 
pure,  and  of  the  same  form  as  the  ferricyanide  of  potassium. 
Its  solution  does  not  affect  the  salts  of  iron,  but  forms  a  rose- 
coloured  precipitate  with  those  of  the  protoxide  of  cobalt.* 

K  phosphide  of  cobalt,  C03P,  was  obtained  by  Rose,  as  a 
grey  powder,  on  passing  hydrogen  over  the  subphosphate  of 
cobalt  ignited  in  a  porcelain  tube.  It  is  also  produced  by 
the  action  of  phosphuretted  hydrogen  on  the  chloride  of 
cobalt,  and  may  be  looked  upon  as  analogous  in  composition 
to  the  former  compound,  II3P. 

*  For  further  details  on  the  cobaltioyanides,  vide  Gmelin's  Handbook  (trans- 
lation), vii.  492-497. 

F  2 


68  COBALT. 

Ammoniacal  salts  of  cobalt. —  Cobalt-salts  treated  with 
excess  of  ammonia  in  a  vessel  from  wliicli  the  air  is  excluded, 
unite  with  the  ammonia,  forming  compounds  to  which  Fremy 
gives  the  name  of  ammonio- cobalt  salts.  Most  of  them  con- 
tain 3  eq.  ammonia  to  1  eq.  of  the  cobalt-salt ;  thus  the  cliloride 
contains  C0CI.3NH3  +  HO :  the  nitrate  C0O.N05.3NH3  + 
2H0.  They  are  mostly  cry  st  alii  sable  and  of  a  rose-colour, 
soluble  without  decomposition  in  ammonia,  but  decomposed  by 
water  with  separation  of  a  basic  salt.  (Fremy.)  H.  Rose,  by 
treating  dry  chloride  of  cobalt  with  ammoniacal  gas,  obtained 
the  compound  C0CI.2NH3;  and  similarly  an  anhydrous  sul- 
phate containing  C0O.SO3.3NH3. 

When  an  ammoniacal  solution  of  a  cobalt  salt  is  exposed  to 
the  air,  oxygen  is  absorbed,  the  liquid  turns  brown,  and  new 
salts  are  formed  containing  a  higher  oxide  of  cobalt  (C02O3  or 
CO2),  and  therefore  designated  generally  ^speroa^idised  ammo- 
niO'Cobalt  salts.  Several  of  these  salts  containing  different 
bases  are  often  formed  at  the  same  time.  Fremy*  distinguishes 
four  classes  of  these  compounds,  viz.,  salts  of  occijcobaltia, 
luteocobaltia,  fitscocobaltia,  and  roseocobaltia. 

The  oxycobaltia-salts  are  formed  by  the  action  of  the  air 
on  concentrated  solutions  of  ammonio-cobalt  salts.  Tlicy  have 
generally  an  ohve  colour,  are  sparingly  soluble  in  the  am- 
moniacal liquid,  and  are  decomposed  by  water,  especially 
when  hot,  with  evolution  of  pure  oxygen,  liberation  of  am- 
monia, and  separation  of  a  green  basic  salt  containing  cobal- 
toso-cobaltic  oxide  CO3O4,  They  contain  5  cq.  of  ammonia 
associated  with  2  eq.  of  a  monobasic  salt  of  bi-oxide  of  cobalt, 
C0O2;  thus  the  nitrate  is  composed  of  2(Co02.N05).5NIi3. 
The  nitrate  and  sulphate  crystallise  in  small  prisms  contain- 
ing water  of  crystallisation  (Fremy). 

The  luteocobaltia-salts  are  formed:  1.  By  the  action  of 
the  air  on  dilute  solutions  of  ammonio-cobalt  salts ;  2.  By  the 
action  of  a  small  quantity  of  water  on  crystallised  oxycobal- 

*  Ann.  Ch.  Phys.,  [3],  xxxv.  257. ;  Chem.  Gaz.  1853,  201. 


SALTS    OF    COBALT.  69 

tia-salts ;  3,  By  treating  the  brown  solution,  formed  by  the 
action  of  oxygen  in  excess  on  ammonio-cobalt  salts,  with  di- 
lute acids;  4.  By  treating  roseocobaltia- salts  with  excess  of 
ammonia.  These  salts  are  of  a  fine  yellow  colour,  crystallise 
readily,  are  tolerably  permanent,  and  resist  for  some  time 
the  action  of  boiling  water.  They  give  no  precipitates  with 
alkaline  phosphates  or  carbonates  at  ordinary  temperatures, 
but  are  decomposed  by  boiling  potash,  with  evolution  of  am- 
monia and  separation  of  C02O3HO.  Dilute  acids  precipitate 
them  from  their  aqueous  solution  in  the  crystalline  state. 
They  contain  1  eq.  of  a  sesquisalt  of  cobalt,  associated  with 
6  eq.  of  ammonia ;  thus,  the  sulphate  =  {Co203.3S03).6NH3 ; 
the  chloride  =  C02CI3.6NH3.  (Fremy.)  This  last  salt  was 
previously  obtained  by  Bogojski*,  who  regarded  it  as  the 
hydrochlorate  of  dicobaltinamine  ClH.NgHgCO  [co  =  fCo]. 
He  likewise  obtained  the  other  salts  of  the  same  base  by 
double  decomposition. 

Fuscocobaltia-salts  are  formed  when  an  ammoniacal  solu- 
tion of  a  protosalt  of  cobalt  is  exposed  to  the  air,  and  by  the 
action  of  water  on  the  oxycobaltia- salts.  They  are  aU  un- 
crystaUisable,  but  may  be  obtained  in  the  solid  state  by  pre- 
cipitation with  alcohol  or  excess  of  ammonia.  They  are  slowly 
decomposed  by  boiling  with  water,  but  quickly  on  the  addition 
of  an  alkali,  with  evolution  of  ammonia,  and  precipitation  of 
hydrated  sesquioxide  of  cobalt.  They  are  of  a  brown  colour, 
and  appear  to  contain  basic  salts  of  sesquioxide  of  cobalt,  united 
with  4  or  5  eq.  of  ammonia.  The  nitrate  contains  C02O3. 
2NO5.4NH3.3HO. 

Ammonio-chloride  of  cobalt,  after  exposure  to  the  air, 
yields  by  evaporation  in  vacuo,  an  uncrystallisable  residue 
having  the  characters  of  the  fuscocobaltia-salts,  but  contain- 
ing a  chlorine-base  ;  its  formula  is  C02CI2O.4NH3.3HO.  By 
exposing  the  solution  of  the  ammonio-chloride  to  the  air  for 

*  J.  pr.  Cliera.  Ivi.  491. 
F  3 


70  COB.\LT. 

two  or  three  weeks,  and  then  boiling  with  sal-ammoniac^ 
roseocobaltiacal  chloride  separates  out  first,  and  afterwards  a 
l)lack  crystalline  compound  containing  CO3CIO3.NH3  +  5HO. 

The  roseocobaltia-salts  are  obtained :  1 .  By  slightly  acidu- 
lating the  solution  of  an  ammonio-cobalt  salt,  w  hich  has  been 
exposed  to  the  air;  2.  By  boiling  the  solution  of  an  ammonio- 
cobalt  salt,  which  has  been  exposed  to  the  air  for  two  or  three 
days,  and  contains  a  fuscocobaltia-salt,  with  a  salt  of  ammonia; 
3.  By  mixing  oxycobaltia-salts  with  boiling  solutions  of  am- 
moniacal  salts.  They  have  a  fine  red  or  rose  colour,  and  some 
of  them  crystallise  readily.  Their  reactions  are  similar  to 
those  of  the  luteocobaltia-salts.  The  nitrate  and  the  neutral 
sulphate  contain  3  eq.  of  C02O3.3NO5,  or  €0203,3803,  with 
5  eq.  ammonia.  There  is  also  an  acid  sulphate  containing 
(Co203.5S03)5NH3  +  5HO,  obtained  by  adding  sulphuric  acid 
in  excess  to  an  ammoniacal  solution  of  sulphate  of  cobalt  which 
has  stood  for  some  days  in  contact  with  the  air.  Baryta- water 
added  to  the  solution  of  the  sulphate,  throws  do^ni  roseocobalti- 
acal oxide,  which  is  rose-colom'cd,  has  a  strong  alkaline  reaction, 
and  decomposes  on  boiling,  giving  off  ammonia  and  depositing 
C02O3.  Tlie  chloride,  C02CI3.5NH3.HO,  is  obtained  by  boiling 
the  ammonio-chloride  of  cobalt,  or  the  chlorine-comiX)und 
C02CI2O.4NH3  (p.  69.),  or  a  salt  of  oxycobaltia,  with  chlo- 
ride of  ammonium  (Fremy) . 

Genth  *  and  F.  Claudetf  have  also  described  a  compound 
■which  appears  to  be  the  same  as  Fremy's  hydrochlorate  of 
30seocobaltia,  although  each  assigns  to  it  a  different  formula. 
"When  sulphate  or  chloride  of  cobalt  is  mixed  with  a  large 
quantity  of  chloride  of  ammonium  and  an  excess  of  ammonia, 
exposed  for  some  time  to  the  air,  and  then  boiled  with  excess 
of  hydrochloric  acid,  a  crimson  powder  gradually  separates, 
oxygen  is  evolved,  and  the  liquid  becomes  colourless.  This 
compound  dissolves  in  244  parts  of  cold  water,  and  in  a  smaller 

*  Ann.  Cli.  Pharm.  Ixxx.  275. ;  Chem.  Gaz.  1851,  266, 
t  Pliil.  Mag.  [4],  ii.  253. ;  Chem.  Soc.  Qu.  J.  iv.  35a 


SALTS    OF    COBALT.  71 

quantity  of  boiling  water,  but  is  decomposed  by  continued 
boiling,  unless  hydrocbloric  acid  be  added ;  in  that  case  a  solu- 
tion is  obtained,  from  which  the  compound  crystallises  on 
cooling  in  ruby- coloured  regular  octohedrons.  Genth  assigns 
to  this  compound  the  formula  C02O3.3NH4CI,  regarding  it  as 
the  chloride  of  a  conjugated  radical  C02O3.3NH4.  Claudet 
finds  it  to  contain  3C1, 2Co,  5N  and  16H,  and  expresses  its  com- 
position by  one  of  the  following  formulae : — 

(NH2C02   )  ,        V  CE     \ 

3NH4CI  +  2NH2C0;         CWNH3NH4  };        C1NK,M  ^.2C1N        2 

(NHNH4  )  ^  ^^^^  ^^^'^ 

According  to  the  two  latter  formulae,  the  compound  is  sup- 
posed to  contain  ammonium  in  which  part  of  the  hydrogen  is 
replaced  by  NH4.  It  might  also  be  regarded  as  the  hydro- 
chlorate  of  pentacobaltosamine  N5H13C02.3HCI,  the  base  being 
formed  of  5  eq.  of  ammonia  in  which  2  eq.  of  hydrogen  are 
replaced  by  cobalt.  Gregory*  assigns  to  it  the  formula 
C02CI3  .  5NH3,  making  it  identical  with  Fremy's  roseoco- 
baltiacal  chloride. 

The  compound  heated  in  a  glass  tube  gives  off  ammonia 
and  sal-ammoniac,  and  leaves  CoCl.  When  the  aqueous  solu- 
tion is  boiled,  ammonia  is  evolved,  and  a  precipitate  formed 
probably  consisting  of  C03O4.3HO,  combined  with  nitride  of 
cobalt.  The  chlorine  compound  treated  with  recently  preci- 
pitated oxide  of  silver,  yields  the  oxygen-compound  of  the  same 
radical ;  and  by  double  decomposition  with  various  silver-  salts, 
the  other  salts  of  the  base. 

The  ammonia  in  all  these  compounds  is  in  a  peculiar  state, 
not  exhibiting  its  usual  basic  properties,  or  being  recognisable 
by  the  usual  reagents  or  replaceable  by  other  bases.  Glaus 
attributes  this  circumstance  to  the  ammonia  being  in  a  passive 
state,  which  is  merely  another  way  of  expressing  the  fact,  but 

*  Ann.  Cli.  Pharm.  Ixxxvii.  125. 
F  4 


72  COBALT. 

affords  no  explanation.  Weltzien  supposes  the  compounds  in 
question  to  contain  compound  ammonium-molecules,  in  which 
1  or  2  at.  hydrogen  are  replaced  by  ammonium  itself  (an 
idea  first  suggested  by  Mr.  Graham),  viz.,  ammo-cobaltammo- 


nium  NHgAmCo,  and  biammo-cobalt ammonium  NHAmjCo 
[the  symbol  Am  standing  for  NH^].  Thus  the  ammonio- 
cobalt  salts  J  containing  2NH3,  may  be  regarded  as  neutral 
salts  of  ammo-cobaltammonium,  and  those  which  contain 
3NH3  as  neutral  salts  of  biammo-cobaltammonium  ;  thus  — 


C0CI.2NH3  =  NH2AmCo.Clj  and 
CoBr.SNHy  =  NHA^o.Br. 

The  fuscocobaltia-salts  may  be  regarded  as  basic  salts  of 
the  sesquioxide  of  ammo-cobaltammonium,  e.  g. — 

C02O3.2NO5.4NH3  =  (NH^cijA-^NOs. 

The  luteocobaltia-s&\ts,  as  neutral  salts  of  the  sesquioxide 
of  biammo-cobaltammonium,  e.  g. — 


C02O3.3NO5.GNH3  =  (NHAm2Co)203.3N05  ; 

The   roseocobaltia-svAts   as   neutral   sesquisalts   containing 
1  at.  of  each  of  the  above-mentioned  ammoniums,  thus — 


Co,Cl3.5NH3  ^NH^AmCo 
NHAmXo 


•CI3; 


And  the  oxycobaltia-salts  as  basic   salts  of  the  same  two 
ammonium-molecules,  e.  g, — 


2CoO2.2SO3.5NH3  =  ^^M;^0 

NHAm2Co 


0,.2S03. 


ESTIMATION    OF    COBALT.  73 


ESTIMATION  OF  COBALT,    AND    METHODS  OF  SEPARATING  IT  FROM 
THE  PRECEDING  METALS. 

Cobalt  is  generally  precipitated  from  its  solutions  by  caustic 
potash.  The  precipitate  is  bluish,  and  consists  of  a  basic  salt, 
which,  however,  when  heated,  is  converted  into  the  hydrated 
protoxide  of  a  dingy  rose  colour.  It  must  then  be  washed  in 
hot  water,  dried  and  ignited  in  an  atmosphere  of  hydrogen, 
by  which  it  is  reduced  to  the  metallic  state,  after  which  it  is 
weighed.  According  to  Beetz*,  the  reduction  to  the  metallic 
state  may  be  dispensed  with,  an  accurate  result  being  obtained 
by  igniting  the  precipitated  oxide  till  it  no  longer  varies  in 
weight,  its  composition  being  then  4C0.C02O3  or  CogO^ ;  but 
the  reduction  by  hydrogen  is  perhaps  the  surer  method. 

Cobalt  is  separated  from  the  alkalies  and  alkaline  earths  by 
sulphide  of  ammonium,  the  black  sulphide  of  cobalt  being 
then  dissolved  in  nitro-hydrochloric  acid,  and  the  oxide  preci- 
pitated by  potash  as  above. 

From  magnesia  it  may  also  be  separated  by  sulphide  of 
ammonium,  sufficient  chloride  of  ammonium  being  added  to 
hold  the  magnesia  in  solution. 

From  alumina  and  glucina  it  is  separated  by  potash. 

The  separation  of  cobalt  from  manganese  is  difficult.  It  is 
best  effected  by  heating  the  mixed  oxides  in  hydrochloric  acid 
gas,  which  converts  them  into  chlorides,  and  then  heating  the 
chlorides  in  a  stream  of  hydrogen,  which  reduces  the  cobalt 
to  the  metallic  state,  but  leaves  the  chloride  of  manganese 
undecomposed ;  the  latter  is  then  dissolved  out  by  water. 
Another  mode  of  separation  is  to  digest  the  mixed  oxides  in  a 
solution  of  pentasulphide  of  calcium,  which  dissolves  the 
sulphide  of  cobalt,  but  leaves  the  sulphide  of  manganese  un- 
dissolved, f 

Cobalt  is  separated  from  iron  in  the  same  manner  as  man- 

*  Pogg.  Ann.  Ixi.  472.  t  Cloez,  J.  Pharm.  [3.]  vii.  157. 


74  NICKEL. 

gancse  (p.  58.),  viz.  by  bringing  the  iron  to  the  state  of 
sesquioxide,  then  adding  chloride  of  ammonium,  neutralising 
^yiih  ammonia,  and  precipitating  the  iron  by  succinate  of 
ammonia. 


SECTION   IV. 

NICKEL. 

Eg.  29-57  or  369'6. 


This  metal  resembles  iron  and  cobalt  more  than  any  others, 
and  is  associated  with  these  metals  in  meteorites,  and  in  most 
of  the  terrestrial  minerals  which  contain  it.  The  principal 
ore  of  nickel  is  arsenical  nickel,  a  mineral  having  the  colour 
of  metallic  copper,  to  which  the  German  miners,  having 
attempted  in  vain  to  extract  copper  from  it,  gave  the  name 
kupfer-nickely  or  false  copper.  This  mineral  was  found  by 
Cronstedt  of  Sweden,  in  1751,  to  contain  a  particular  metal, 
which  he  called  nickel.  Nickel  imparts  a  remarkable  white- 
ness to  the  metallic  alloys  which  contain  it,  on  which  account 
it  has  come  of  late  to  be  valued  in  the  arts,  being  added  to 
brass  to  form  the  well-known  imitations  of  silver. 

The  metal  is  prepared  from  the  native  arsenide,  or  from  an 
artificial  arsenide  called  speiss,  which  contains  about  54  per 
cent  of  nickel,  and  has  been  observed  by  Wohler  to  occur  in 
octohedrons  with  a  square  base,  having  the  composition  NiyAs. 
Speiss  is  a  metallic  substance  which  collects  at  the  bottom  of 
the  crucibles  in  which  smalt  or  cobalt-blue  is  prepared.  In 
that  operation,  a  mixture  of  quartzy  sand,  potashes,  and  the 
roasted  ore  of  cobalt  is  fused.  The  previous  roasting  never 
being  perfect,  a  part  of  the  metals  escapes  oxidation ;  and 
hence  when  the  mixture  described  is  fused,  the  cobalt,  which 


NICKEL.  75 

is  more  oxidable  than  nickel  and  copper,  reacts  upon  the 
oxides  of  these  metals^  and  reduces  them,  while  it  is  itself 
oxidated :  the  nickel  and  copper  concentrate  in  the  speiss, 
while  the  smalt  contains  scarcely  any  of  them.  A  salt  of 
nickel  may  be  obtained  by  treating  speiss  in  fine  powder  with 
an  equal  weight  of  sulphuric  acid,  diluted  with  four  or  five  times 
its  bulk  of  water,  and  gradually  adding  an  equal  weight  of 
nitric  acid,  which  occasions  the  oxidation  of  both  the  nickel 
and  the  arsenic.  The  green  solution  thus  obtained,  when 
cooled  and  allowed  to  stand  for  twenty-four  hours,  deposits 
much  arsenious  acid,  from  which  it  may  be  separated  by  filtra- 
tion. A  quantity  of  carbonate  of  potash,  equal  to  half  the 
weight  of  the  speiss,  is  then  added  to  the  solution,  which  is 
concentrated  and  set  aside  to  crystallise.  The  double  sulphate 
of  nickel  and  potash,  NiO.SOg  +  KO.SOg-f  6H0,  forms  easily, 
and  may  be  obtained  free  from  arsenic  by  a  second  crystallisa- 
tion. (Dr.  Thomson.)  The  perfect  separation  of  small  quan- 
tities of  cobalt  and  copper,  which  these  crystals  may  still 
contain,  requires  additional  processes.*  With  the  view  of  ob- 
taining the  metal,  the  insoluble  oxalate  of  nickel  may  be  preci- 
pitated from  the  preceding  salt  by  oxalate  of  ammonia,  washed, 
dried,  and  ignited  gently  in  a  covered  crucible.  The  oxalic  acid 
reduces  the  oxide  of  nickel,  and  the  metal  remains  in  a  spongy 
state.  It  is  pyrophoric,  like  manganese  and  iron  prepared  in  the 
same  manner,  if  the  temperature  of  reduction  has  been  low.  To 
obtain  the  metal  in  a  solid  mass,  it  should  be  fused  in  a  crucible 
covered  with  pounded  glass.  The  oxide  of  nickel  is  very  easily 
reduced  both  by  carbonic  oxide  and  by  hydrogen. 

Nickel,  when  free  from  cobalt,  is  silver- white,  unalterable 
in  air,  and  highly  ductile.  Its  density,  according  to  Richter, 
is  8*279,  and  after  being  forged  8*666.  Nickel  is  magnetic 
nearly  to  the  same  extent  as  iron.  Magnets  composed  of  this 
metal  lose  their  polarity  at  630°  (Faraday).  It  is  somewhat 
more  fusible  than  iron.     Nickel  forms  two  oxides  correspond- 

*  Bcrzelius,  Traite.  tcm.  i.  p.  486. ;  see  also  pp.  78—80.  of  this  volume. 


76  NICKEL. 

ing  with  the  protoxide  and  sesquioxide  of  iron ;  but  the  doable 
compound  of  the  two  oxides  of  nickel^  corresponding  with  the 
black  oxide  of  iron,  has  not  been  observed. 

Protoxide  of  nickel,'NiO,S7'67j  or  469'6,  may  be  obtained 
by  the  ignition  of  the  carbonate  or  nitrate  of  nickel,  or  by  pre- 
cipitation from  its  salts  by  an  alkali,  as  a  dark  ash-coloured 
powder,  or  as  a  bulky  hydrate  of  an  apple- green  colour,  NiO 
HO.  Oxide  of  nickel  is  very  soluble  in  acids,  but  not  in  pot- 
ash or  soda.  Ammonia  dissolves  it,  and  forms  an  azure -blue 
solution,  from  which  oxide  of  nickel  is  precipitated  by  potash, 
baryta,  and  strontia,  having  a  considerable  tendency  to  com- 
bine with  salifiable  bases.  The  solutions  of  its  salts  have  all  a 
green  colour,  much  more  intense  than  tliat  of  the  ferrous  salts. 
They  are  not  precipitated  by  hydrosulphuric  acid  when  a 
strong  acid  is  present,  but  afford  a  black  sulphide  with  alka- 
line sulphides.  Carbonate  of  nickel  is  of  a  pale  green-colour 
and  soluble  in  carbonate  of  ammonia. 

Peroxide  or  sesquioxide  of  nickel,  Ni203,  is  obtained  as  a 
black  powder,  by  exposing  the  hydrated  protoxide  suspended 
in  water  to  a  stream  of  chlorine  gas.  It  does  not  combine  with 
acids,  and  in  other  respects  resembles  sesquioxide  of  cobalt. 

Besides  a  protosulphide,  NiS,  a  subsuljjhide  of  nickel,  ^\2^, 
is  formed,  like  that  of  manganese,  by  decomposing  the  ignited 
sulphate  of  nickel  with  hydrogen.  A  bisulphide  of  nickel  also 
exists  in  combination  as  a  constituent  of  the  mineral  nickel- 
glance,  NiSj.NiAs. 

Chloride  of  nickel  NiCl,  forms  a  solution  of  an  emerald- 
green  colour,  and  yields  by  evaporation  a  hydrated  salt  of  the 
same  colour,  which  becomes  yellow  when  deprived  of  its  water 
of  crystallisation.  Chloride  of  nickel,  sublimed  at  a  high  tem- 
perature without  access  of  air,  forms  golden  scales  which 
dissolve  with  difficulty. 

Sulphate  of  nickel  crystallises  from  a  strong  solution  in  slen- 
der green  prisms,  isomorphous  with  Epsom  salt,  of  which  the 
composition  is  NiO-SOg^-  7H0.     At  a  higher  temperature,  it 


ESTIMATION   OF  NICKEL.  Tt 

crystallises  with  6  eq.  of  water  NiO.SOa  +  CHO,  like  the 
magnesia  and  cobalt  salts,  and  in  the  same  form.  Mitscher- 
lich  made  the  singular  observation,  that  when  the  crystals 
containing  7  eq.  of  water  are  exposed,  in  a  close  glass  vessel, 
to  a  day  of  sunshine,  or  kept  for  some  time  in  a  temperate 
place,  the}'^  change  their  form,  becoming  a  mass  of  small  crys- 
tals, of  which  the  form  is  the  regular  octohedron.  The  original 
crystals  become  opaque  from  this  change,  but  lose  none  of 
their  combined  water.  Sulphate  of  nickel  forms  the  usual 
double  salts  with  the  sulphates  of  potash  and  ammonia. 

Nickel  also  forms  ammonio -compounds  analogous  to 
the    ammonio-cobalt    salts;     e.  g,   the  ammonio-chloride  — 

SNHg.NiCl  =  NHAm2Ni.Cl ;  ammonio-sulphate  —  3NH3. 
NiS04  =  NHAm2Ni.S04,  &c. 

The  useful  white  alloy  of  nickel,  German  silver  or  packfong, 
is  formed  by  fusing  together  100  parts  of  copper,  60  of  zinc, 
and  40  of  nickel. 

ESTIMATION   OF  NICKEL,   AND  METHODS  OF  SEPARATING   IT  FROM 
THE    PRECEDING    METALS. 

Nickel  isbest  precipitated  from  its  solutions  by  caustic  potash 
which  throws  down  an  apple-green  precipitate  of  the  hydrated 
protoxide,  and  if  the  liquid  be  heated,  leaves  not  a  trace  of  nickel 
in  the  solution.  The  precipitate  must  be  washed  with  hot 
water,  dried,  ignited,  and  weighed ;  it  then  consists  of  pure 
protoxide  of  nickel,  containing  78*57  per  cent  of  the  metal. 

In  separating  nickel  from  other  metals,  it  is  often  necessary 
to  precipitate  it  by  sulphide  of  ammonium;  this  precipitation 
is  attended  with  difficulties,  because  the  sulphide  of  nickel  is 
somewhat  soluble  in  the  alkaline  sulphide.  To  make  the  pre- 
cipitation as  complete  as  possible,  Rose  directs  that  the  solu- 
tion be  diluted  with  a  considerable  quantity  of  water,  and  then 
treated  with  sulphide  of  ammonium,  as  nearly  colourless  as  it 
can  be  obtained,  avoiding  a  large  excess  of  the  precipitant  and 


78  NICKEL. 

likewise  an  excess  of  ammonia ;  the  glass  is  then  to  be  covered 
up  with  filtering  paper,  and  left  in  a  warm  place.  Under  these 
circumstances,  the  excess  of  sulphide  of  ammonium  is  decom- 
posed by  the  oxygen  and  carbonic  acid  of  the  air,  without  risk 
of  the  sulphide  of  nickel  being  oxidised.  As  soon  as  the  super- 
natant liquid  has  lost  its  brown  colour,  the  precipitate  is  col- 
lected on  a  filter  and  washed,  as  quickly  as  possible,  with 
water  containing  a  little  sulphide  of  ammonium.  It  must  then 
be  dissolved  in  nitro-hydrochloric  acid,  and  the  nickel  preci- 
pitated by  potash  as  above. 

The  methods  of  separating  nickel  from  all  the  preceding 
metals  except  cobalt,  are  the  same  as  those  given  for  cobalt 
(p.  73.). 

The  separation  of  nickel  from  cobalt  itself  is  diflBicult.  The  be3t 
method  is  perhaps  that  given  by  H.  Rose*,  depending  on  the 
fact  that  protoxide  of  cobalt  in  solution  is  converted  by  chlo- 
rine into  sesquioxide,  whereas  with  nickel  this  change  does 
not  take  place.  The  metals  or  their  oxides  being  dissolved  in 
excess  of  hydrochloric  acid,  the  solution  is  diluted  with  a  large 
quantity  of  water,  about  a  pound  of  water  to  a  gramme  of  the 
metals  or  their  oxides.  Chlorine  gas  is  then  passed  through 
the  solution  for  several  hours,  till  in  fact  the  space  above  the 
liquid  becomes  permanently  filled  with  the  gas  ;  carbonate  of 
baryta  is  then  added  in  excess,  the  whole  left  to  stand  for  12  or 
18  hours,  and  shaken  up  from  time  to  time.  The  precipitate, 
consisting  of  sesquioxide  of  cobalt  and  carbonate  of  baryta,  is 
then  collected  on  a  filter,  and  washed  with  cold  water.  The 
filtered  liquid,  which  has  a  pure  green  colour,  contains  all  the 
nickel  without  a  trace  of  cobalt.  The  precipitate  is  boiled 
with  hydrochloric  acid  to  convert  the  sesquioxide  of  cobalt  into 
protoxide,  and  dissolve  it  together  ^dth  the  baryta ;  the  latter 
is  then  precipitated  by  sulphuric  acid,  and  the  cobalt  from  the 
filtrate  by  potash.  The  nickel  is  also  precipitated  by  potash 
after  the  removal  of  any  baryta  that  the  solution  majr  contain 

*  ITaiulbuch  dor  Analyiisclicn  Chemie  (Corlin,  1S51),  ii.  10k 


SEPARATION  OF  NICKEL  FROM  COBALT.  79 

by  sulphuric  acid.  This  method,  if  properly  executed,  gives 
very  exact  results.  The  chief  precautions  to  be  attended  to, 
are  to  add  a  large  excess  of  chlorine,  and  not  to  filter  too  soon, 
because  the  precipitation  of  sesquioxide  of  cobalt  by  carbonate 
of  baryta  takes  a  long  time. 

Liebig  has  given  several  methods  of  separating  these  two 
metals,  founded  on  the  difference  of  their  reactions  with 
cyanide  of  potassium.  1.  The  oxides  of  the  two  metals  are 
treated  with  hydrocyanic  acid  and  then  with  potash,  and  the 
liquid  warmed  till  the  whole  is  dissolved  (pure  cyanide  of 
potassium,  free  from  cyanatemay  also  be  used  as  the  solvent). 
The  reddish-yellow  solution  is  boiled  to  expel  free  hydro- 
cyanic acid,  whereupon  the  cobaltocyanide  of  potassium 
(K2CoCy3),  formed  in  the  cold,  is  converted  into  cobalticya- 
nide  (K3Co2Cy6),  while  the  nickel  remains  in  the  form  of 
cyanide  of  nickel  and  potassium  (KNiCy2).  Pure  and  finely- 
divided  red  oxide  of  mercury  is  then  added  to  the  solution 
while  yet  warm,  whereby  the  whole  of  the  nickel  is  precipi- 
tated partly  as  oxide,  partly  as  cyanide,  the  mercury  taking 
its  place  in  the  solution.  The  precipitate  contains  all  the 
nickel,  together  with  excess  of  mercuric  oxide  ;  after  washing 
and  ignition,  it  yields  pure  oxide  of  nickel.  The  filtered 
solution  contains  all  the  cobalt  in  the  form  of  cobalticyanide 
of  potassium.  It  is  supersaturated  with  acetic  acid,  boiled 
with  sulphate  of  copper,  which  precipitates  the  cobalt  in 
the  form  of  cobalticyanide  of  copper  (Cu3Co2Cyg.7HO), 
and  the  precipitate  retained  in  the  liquid  at  a  boiling-heat 
till  it  has  lost  its  glutinous  character.  It  is  then  washed, 
dried,  and  ignited,  dissolved  in  hydrochloric  acid  mixed  with 
a  little  nitric  acid,  the  copper  precipitated  by  hydrosulphuric 
acid,  and  the  filtrate,  after  boiling  for  a  minute  to  expel  the 
excess  of  that  gas,  mixed  with  boiling  caustic  potash  to  preci- 
pitate the  cobalt.* — 2.  Instead  of  adding  the  oxide  of  mercury, 
the  solution  containing  the  mixed  cyanides  may,  after  cooling, 

*  Ann   Ch.  Pharm.  Ixv.  214. 


80  NICKEL. 

be  supersaturated  with  chlorine,  the  precipitate  of  cyanide 
of  nickel  thereby  produced  being  continually  redissolved  by 
caustic  potash  or  soda.  The  chlorine  produces  no  change  on 
the  cobalticyanide  of  potassium,  but  decomposes  the  nickel- 
compound,  the  whole  of  the  nickel  being  ultimately  preci- 
pitated in  the  form  of  black  sesquioxide.* 

Liebig's  first  methodf  which  consisted  in  treating  the  solution 
of  the  mixed  cyanides  with  excess  of  hydrochloric  or  sulphuric 
acid,  whereby  the  nickel  was  precipitated  as  cobalticyanide  of 
nickel,  leaving  a  solution  of  pure  cobalticyanide  of  potassium, 
has  been  found,  both  by  himself  and  others,  not  to  give  per- 
fectly satisfactory  results.  The  method  by  oxalic  acid  (p.  75.), 
and  the  precipitation  of  nickel  from  an  ammoniacal  solution 
of  the  two  metals  by  potash  (p.  76.)  arc  not  sufficiently  accu- 
rate for  quantitative  analysis. 

r.  Claudet  proposes  to  separate  cobalt  from  nickel  and 
other  metals  in  the  form  of  the  ammonio-compound  described 
on  page  70.,  that  compound  being  very  insoluble,  while  cor- 
responding compounds  of  the  other  metals  do  not  appear  to  be 
formed  under  the  same  circumstances. 

The  separation  of  cobalt  from  nickel  (also  from  zinc  and 
the  previously  described  metals)  may  likewise  be  effected  by 
means  of  St.  Evre's  yellow  compound,  which  is  regarded  by 
A.  Stromeyer  as  a  nitrite  of  cobaltic  oxide  and  potash 
(p.  65.).  The  solution  containing  the  mixed  metals  is  diluted 
with  water  till  about  300  parts  of  water  are  present  to 
1  part  of  protoxide  of  cobalt ;  a  somewhat  concentrated  solution 
of  nitrite  of  potash  J  then  added,  and  a  sufficient  quantity  of 
acetic  acid  to  redissolve  any  precipitated  carbonates  ;  and  the 


*  Ann.  Ch.  Pharm.  Ixxxvii.  128.  t  Ibid.  xli.  291. 

+  The  nitrite  of  potash  is  prepared  by  fusing  1  part  of  nitre  in  contact 
with  2  parts  of  metallic  lead,  first  at  a  low  and  then  at  a  bright-red  heat,  ex- 
hausting the  cooled,  mass  with  water,  precipitating  a  small  quantity  of  lead 
by  carbonic  acid,  and  then  by  sulphide  of  ammonium,  evaporating  to  dryness, 
and  heating  to  the  melting-point  to  decompose  any  hyposulphite  of  potash 
that  may  have  been  formed. 


ZINC.  81 

solution  left  to  stand  for  12  to  24  hours  in  a  covered  vessel, 
then  filtered  and  washed,  first  with  acetate  of  potash,  after- 
wards with  alcohol.  The  precipitate  contains  all  the  cobalt 
in  the  form  of  the  above-mentioned  salts,  and  none  of  the 
other  metals.* 


SECTION    V. 

ZINC 

32-52 ;  Zn.  or  Eg.  406*6. 

The  principal  ores  of  zinc  are  calamine,  or  the  carbonate,  a 
pulverulent  mineral  generally  of  a  reddish  or  flesh  colour,  and 
zinc -blende J  a  massive  mineral  of  an  adamantine  lustre,  and 
often  black.  The  oxide,  from  the  carbonate  or  from  the 
calcined  sulphide,  is  mixed  with  about  ^  of  its  weight  of 
carbonaceous  matter,  and  heated  to  a  low  white  heat  in  re- 
torts, or  similar  vessels  of  earthenware  or  iron.  The  zinc  is 
then  reduced  and  volatilised,  and  condenses  in  the  colder  part 
of  the  apparatus. 

In  Silesia,  the  mixture  of  zinc-oxide  and  charcoal,  or  coke, 
is  heated  in  muffles  (Fig.  4.)  3  feet  long  and  18  inches  high. 

Fig.  4. 


six  of  which  are  laid  in  one  furnace  (Fig.  5.),  three  side  by 
side.  The  evolved  mixture  of  carbonic  oxide  and  zmc -vapour 
passes  from  the  upper  and  fore  part  of  the  muffles  M,  through 

*  A.  Stromeyer,  Ann.  Ch.  Pharrn.  xcvi.  p.  218.  ;  see  also  Liebig  and  Kopp'a 
Jaliresbericht,  1854,  p.  357. 

VOL.  II.  G 


82 


ZINC. 


a  knee-shaped  channel  b  c  d^  and  the  zinc  condenses 
therein  and  drops  down  from  the  lower  aperture  d  into  the 
reservoirs  t  (Fig.  5.)  placed  beneath. 

Fig.  5. 


Fig.  6. 


Part  of  the  zinc- vapour,  and  likewise  some  cadmium -vapour, 
escapes  uncondensed,  together  with  the  carbonic  oxide  gas, 
and  bums  in  the  air,  producing  the  substance  called  Silesian 
zinc-flowers.  Silesia  furnishes  the  greater  part  of  the  zinc 
used  in  the  arts. 

In  Belgium,  the  reduction  is   performed  in  earthenware 
tubes,  laid  side  by  side ;  and  tlie  zinc  as  it  condenses  in  the 

fore  part  of  these  tubes,  is  scraped 
out  from  time  to  time  in  the  hquid 
state. 

In  England,  a  number  of  cast- 
iron  pots  are  arranged  in  a  circle  in 
the  furnace  (Fig.  6.).  Through  tlie 
bottom  of  each  of  these  pots,  there 
passes  an  iron  tube  / 1',  which  is  con- 
tinued downwards  through  an  aper- 
ture in  the  bottom  of  the  furnace. 
The  upper  end  of  the  tube  is  stopped 
with  a  plug  of  wood,  which  is 
cliarrcd  during  the  operation,  and 
l)ccomes  sufficiently  porous  to  allow 


ZINC.  83 

the  passage  of  the  zinc-vapour,  but  at  the  same  time  prevents 
the  solid  matter  from  falling  through.  Each  pot  is  fitted  with 
a  cover  well  luted  with  clay.  The  fire-place  F,  is  in  the 
middle.  The  distilled  zinc  condenses  in  the  tubes  //',  and 
falls  in  drops  into  a  receiver  u,  placed  beneath.  This  process 
is  called  destillatio  per  descensum. 

Zinc  may  be  purified  by  a  second  distillation  in  a  porcelain 
retort ;  but  the  first  portions  of  that  metal  which  come  over 
should  be  rejected,  as  they  generally  contain  cadmium  and 
arsenic. 

Zinc  is  a  white  metal,  with  a  shade  of  blue,  capable  of 
being  polished  and  then  assuming  a  bright  metallic  lustre. 
It  is  usually  brittle,  and  its  fracture  exhibits  a  crystalline 
structure.  But  zinc,  if  pure,  may  be  hammered  into  thin 
leaves,  at  the  usual  temperature ;  and  commercial  zinc,  which 
is  impure  and  brittle  at  a  low  temperature,  acquires  the 
same  malleability  between  210°  and  300°:  it  may  then  be 
laminated ;  and  the  metal  is  now  consumed  in  the  form 
of  sheet  zinc  for  a  variety  of  useful  purposes.  At  400°  it 
again  becomes  brittle,  and  may  be  reduced  to  powder  in  a 
mortar  of  that  temperature.  The  density  of  cast  zinc  is 
6*862,  but  it  may  be  increased  by  forging  to  7*21.  Its  point 
of  fusion  is  773°  (Daniell).  At  a  red  heat,  zinc  rises  in 
vapour  and  takes  fire  in  the  air,  burning  with  a  white  flame  like 
that  of  phosphorus ;  the  white  oxide  produced  is  carried  up 
mechanically  in  the  air,  although  itself  a  fixed  substance. 
Laminated  zinc  is  a  valuable  substance,  from  its  little  disposi- 
tion to  undergo  oxidation.  When  exposed  to  air  or  placed  in 
water,  its  surface  becomes  covered  with  a  grey  film  of  sub- 
oxide, which  does  not  increase ;  this  film  is  better  calculated 
to  resist  both  the  mechanical  and  chemical  effects  of  other 
bodies  than  the  metal  itself,  and  preserves  it.  Zinc  dissolves 
with  facility  in  dilute  hydrochloric,  sulphuric  and  other 
hydrated  acids,  by   substitution  for   hydrogen.     In  contact 

G   2 


:84  ZINC. 

with  iron,  it  protects  the  latter  from  oxidation  in  any  saline 
fluid. 

Zinc  appears  to  form  three  oxides,  the  suboxide  above  re- 
ferred to,  the  protoxide,  and  a  peroxide,  which  last  is  produced 
when  the  hydrated  protoxide  is  acted  upon  by  a  solution  of 
peroxide  of  hydrogen ;  but  of  these,  the  first  and  last  have 
not  been  studied,  and  the  protoxide  is,  therefore,  the  only 
well  known  oxide  of  zinc. 

Protoxide  of  zinc ;  ZnO;  40'52  or  5066.  —  This  oxide 
may  be  obtained,  in  the  form  of  an  anhydrous  white  powder, 
by  the  combustion  of  the  metal  in  a  stoneware  crucible,  or  as 
a  white  hydrate,  by  precipitation  from  its  salts  by  an  alkali. 
It  is  of  a  yellow  colour  at  high  temperatures,  but  becomes 
colourless  again  on  cooling.  By  the  oxidation  of  zinc  in  air 
and  water,  without  access  of  carbonic  acid,  a  hydrate,  3ZnO 
-f  HO,  has  been  obtained  in  crystalline  needles  (Mitscherlich). 

Oxide  of  zinc  combines  with  acids  and  forms  salts,  which 
are  colourless,  like  those  of  magnesia.  Caustic  alkalies 
form  with  zinc-salts  a  white  gelatinous  precipitate  of  the 
hydrated  oxide,  soluble  in  excess  of  the  alkali.  Carbonate  of 
potash  or  soda  throws  down  white  carbonate  of  zinc,  insoluble 
in  excess ;  carbonate  of  ammonia,  the  same  precipitate,  soluble 
in  excess.  Ferrocyanide  of  potassium,  and  the  alkaline  phos- 
phates and  arseniates,  also  foiTQ  white  precipitates.  Zinc- 
salts  containing  a  strong  acid  in  excess,  are  not  affected  by 
hydrosulphuric  acid,  but  give  a  white  hydrated  sulphide  with 
alkaline  sulphides.  A  solution  of  acetate  of  zinc  is  readily 
decomposed  by  hydrosulphuric  acid. 

The  native  sulphide  of  zinc,  or  zinc-blende,  ZnS,  crystal- 
lises in  octohedrons.  Its  colour  is  variable,  being  sometimes 
yellow,  red,  brown,  or  black. 

Chloride  of  zinc,  ZnCl,  is  produced  by  the  combustion  of 
zinc  in  chlorine,  and  by  dissolving  the  metal  in  hydrochloric 
acid.  It  is  fusible  at  212°,  volatile  at  a  red  heat,  and  perhaps 
the  most  deliquescent  of  salts.     Chloride  of  zinc-ammonium, 


SALTS    OF    ZINC.  85 

NHgZn.Cl,  is  obtained,  according  to  Ritthansen,  in  white 
prismatic  crystals,  when  zinc  and  copper,  or  zinc  and  silver, 
are  placed  in  contact  in  a  solution  of  sal-ammoniac,  or  by  the 
action  of  zinc  on  a  solution  of  sal-ammoniac  containing 
chloride  of  copper. 

Iodide   of  zinc   is   formed   by  digesting  iodine,  zinc,   and 
water  together,  and  resembles  the  chloride.     The  compound 


Znl.SNHg,  or  NH2(NH4)Zn.I,  forms  crystals  belonging  to 
the  rhombic  system  (Rammelsberg) . 

The  neutral  carbonate  of  zinc  forms  the  ore  called 
calamine.  When  precipitated  by  an  alkaline  carbonate,  the 
salts  of  zinc,  like  those  of  magnesia,  yield  the  neutral  car- 
bonate in  combination  with  hydrated  oxide,  2(ZnO.C02) 
+  3(ZnO.HO).  The  mineral  substance,  zinc-bloom,  is  of  the 
same  composition.  Precipitated  in  the  cold,  the  carbonate  is 
ZnO.COg  +  2(ZnO.HO),  but  is  contaminated  with  sulphate 
of  soda  (Mitscherlich). 

Sulphate  of  zinc,  White  vitriol,  ZnO.SOg  +  THO. — This  salt 
is  formed  by  the  oxidation  of  the  native  sulphide  at  high 
temperatures,  or  by  dissolving  the  metal  in  dilute  sulphuric 
acid.  It  crystallises  in  colourless  prismatic  crystals,  contain- 
ing 7  eq.  of  water,  the  form  of  which  is  a  right  rhombic  prism. 
This,  like  all  the  other  magnesian  sulphates,  gives  up  6  eq.  of 
its  water  at  about  212°,  while  the  seventh  or  constitutional 
equivalent  requires  a  heat  of  400°  to  expel  it.  The  crystals 
are  soluble  in  24  times  their  weight  of  water,  at  the  usual 
temperature,  and  fuse  in  their  water  of  crystallisation  when 
heated.  The  salt  also  crystallises  above  86°,  with  6  eq.  of 
water,  in  oblique  rhombic  prisms  (Mitscherlich).  According 
to  Kiihn,  another  hydrate  is  formed  and  precipitated  as  a 
white  powder,  containing  2  eq.  of  water,  when  a  concentrated 
solution  of  sulphate  of  zinc  is  mixed  with  oil  of  vitriol.  Sul- 
phate of  zinc  forms  the  usual  double  salt  with  sulphate  of  potash, 
ZnO.SOa  +  KO.SOg-l-eHO.    The  double  sulphate  of  zinc  and 

o  3 


86  ZINC. 

soda  contains  4  atoms  of  water,  ZnO.S03  +  NaO.S03  +  4HO. 
It  is  formed  by  a  singular  decomposition  (I.  228.).  "When  a 
solution  of  the  sulphate  is  mixed  with  a  quantity  of  alkali 
less  than  suflficient  for  complete  precipitation,  a  subsulphate  of 
zinc  precipitates,  which,  according  to  the  analyses  of  several 
chemists,  contains  4  eq.  of  oxide  of  zinc  to  1  eq.  of  sulphuric 
acid,  besides  water.  A  concentrated  solution  of  sulphate  of 
zinc  dissolves  the  preceding  subsalt,  and,  when  saturated, 
contains  a  compound  of  1  eq.  of  acid  and  2  eq.  of  base,  ac- 
cording to  Schindler,  and  docs  not  crystallise.  From  this 
solution,  Schindler  obtained  the  former  insoluble  subsalt 
with  two  different  proportions  of  water,  in  long  crystalline 
needles,  containing  lOHO,  by  spontaneous  evaporation  of  the 
solution,  and  in  brilliant  crystalline  plates  containing  2 HO, 
which  were  deposited  on  boiling  the  solution.  By  diluting 
the  same  solution  with  a  large  quantity  of  water,  he  also  ob- 
tained another  subsalt,  as  a  light  bulky  precipitate,  which 
contained  1  eq.  of  acid,  8  eq.  of  oxide  of  zinc,  and  2  eq.  of 
water.  The  insoluble  matter,  which  precipitates  when  sul- 
phate of  zinc-ammonium  (NH3Zn)O.S03  is  thrown  into 
water,  is  considered  by  Kane  as  a  third  subsulphate  of 
zinc,  containing  1  eq.  of  acid,  6  eq.  of  oxide  of  zinc,  and 
10  eq.  of  water.  All  these  subsulphates  afford  neutral 
sulphate  of  zinc  to  water,  after  being  heated  to  redness ;  so 
that,  whatever  their  constitution  may  be  when  hydrated, 
it  is  certaiidy  different  from  what  it  is  in  their  anhydrous 
condition. 

Nitrate  of  zinc,  ZnO.NOg -1-6110,  is  very  soluble  in  water, 
and  moderately  deliquescent. 

Phosphate  of  zinc,  ZnOj.HO.POg  4-  2HO,  is  obtained  in 
minute  silvery  plates,  which  are  nearly  insoluble,  on  mixing 
dilute  solutions  of  phosphate  of  soda  and  sulphate  of  zinc. 

Silicate  of  zinc  is  foimd  as  a  crystalline  mineral,  which  has 
received  the  name  of  the  electrical  oxide  of  zinc,  because  it 
acquires,   like   the   tourmalin,    a   high   degree   of    electrical 


ESTIMATION    OF    ZINC.  87 

polarity  when  heated.     It  contains  water,  and  may  be  repre- 
sented by  the  formula  2(3ZnO.Si03)  +3H0. 

The  most  important  alloys  of  zinc  are  those  with  copper, 
which  form  the  varieties  of  brass.  Zinc  also  combines  readily 
with  iron,  and  is  contaminated  by  that  metal,  when  fused  in 
an  iron  crucible. 


OTHER    METALS. 

Zinc  is  precipitated  from  its  solutions  by  carbonate  of  soda, 
which,  when  added  in  excess  and  boiled  with  the  solu- 
tion, throws  down  carbonate  of  zinc.  It  is  best,  however^ 
to  pour  the  zinc-solution  into  the  hot  solution  of  the  alkaline 
carbonate,  because,  in  that  case,  we  may  be  sure  of  not  form- 
ing a  basic  salt.  If  the  zinc-solution  contains  ammoniacal 
salts,  it  must  be  boiled  with  a  quantity  of  carbonate  of  soda 
sufficient  to  decompose  those  salts ;  then  evaporated  to  dry- 
ness ;  the  residue  treated  with  a  large  quantity  of  water  to 
dissolve  out  the  soluble  salts;  and  the  carbonate  of  zinc 
collected  on  a  filter  and  weU  washed  with  hot  water.  The 
evaporation  should  be  conducted  as  quickly  as  possible.  The 
carbonate  of  zinc,  when  dried  and  ignited,  yields  oxide  of  zinc 
containing  80*26  per  cent,  of  the  metal. 

In  separating  zinc  from  other  metals,  it  is  often  necessary 
to  precipitate '  by  sulphide  of  ammonium.  If  the  solution  is 
acid,  it  must  be  previously  neutralised  by  ammonia.  The 
precipitate  must  not  be  thrown  on  the  filter  immediately,  but 
left  to  settle  down  completely,  after  which  the  clear  liquid 
must  first  be  passed  through  the  filter,  and  then  the  preci- 
pitate thrown  on  it.  If  this  precaution  be  neglected,  the 
sulphide  of  zinc  will  stop  up  the  pores  of  the  filter.  The 
precipitate  is  washed  with  water  containing  a  little  sulphide 
of  ammonium ;  then  dissolved  in  hydrochloric  acid ;  the  solution 

o  4 


88  ZINC. 

boiled  to  drive  off  the  hydrosulphuric  acid;  and  the  zinc 
precipitated  by  carbonate  of  soda  as  above. 

Zinc  is  separated  from  the  alkalies  and  alkaline  eartJis 
(baryta,  strontia,  and  lime)  by  means  of  sulphide  of  am- 
monium. In  the  case  of  the  alkaline  earths,  however,  great 
care  must  be  taken  to  prevent  the  ammoniacal  liquid  from 
absorbing  carbonic  acid  from  the  air,  as  that  would  occasion 
a  precipitation  of  the  earth  in  the  form  of  carbonate.  For 
this  purpose,  the  filtration  must  be  effected  as  quickly  as 
possible,  and  the  liquid  well  protected  from  the  air.  The 
separation  of  zinc  from  baryta  may  also  be  effected  by  sul- 
phuric acid,  and  from  lime  by  oxalate  of  ammonia. 

From  magnesia^  zinc  may  be  separated  by  sulphide  of  am- 
monium, a  sufficient  quantity  of  chloride  of  ammonium  being 
previously  added  to  prevent  the  precipitation  of  the  magnesia. 
Or  the  separation  may  be  effected  by  converting  the  zinc  and 
magnesia  into  acetates,  and  precipitatmg  the  zinc  as  sulphide 
by  hydrosulphuric  acid. 

The  separation  of  zinc  from  alumina  and  glucina  may  also 
be  effected  by  converting  the  two  bases  into  acetates  and  pre- 
cipitating the  zinc  by  hydrosulphuric  acid ;  or  hy  dissolving 
in  potash,  and  precipitating  the  zinc  by  hydrosulphuric  acid  ; 
but  the  former  method  is  to  be  preferred. 

The  conversion  into  acetates  and  precipitation  by  hydrosul- 
phuric acid  likewise  serves  to  separate  zinc  from  zirconia, 
yttria,  thorina,  and  manganese.  The  separation  from  man- 
ganese may  also  be  effected  by  converting  the  two  metals 
into  chlorides,  passing  chlorine  gas  through  the  solution  to 
convert  the  manganese  into  bioxide,  and  completing  the  pre- 
cipitation of  the  latter  by  carbonate  of  baryta. 

From  iron,  zinc  may  be  separated  by  ammonia,  or  better  by 
succinate  of  ammonia,  the  same  precautions  being  used  as  in 
the  separation  of  iron  from  manganese  by  the  same  method 
(p.  58.).  The  iron  (in  the  state  of  sesquioxide)  may  also  be 
precipitated  by  carbonate  of  lime  or  carbonate  of  baryta. 


CADMIUM.  89 

From  cobalt  and  nickel,  zinc  is  separated  "by  dissolving  the 
oxides  of  both  metals  in  excess  of  acetic  acid,  and  precipi- 
tating the  zinc  by  hydrosulphuric  acid.  Nickel  and  cobalt 
are  completely  precipitated  by  hydrosulphuric  acid  from  the 
neutral  solutions  of  their  acetates,  but  not  when  a  consider- 
able excess  of  acetic  acid  is  present.  But  in  separating  zinc 
from  cobalt  and  nickel  in  this  manner,  a  small  quantity  of  the 
latter  metals  is  generally  precipitated  with  the  zinc  towards 
the  end  of  the  process,  the  precipitate  then  becoming  greyish 
black.  In  that  case  it  must  be  redissolved  in  hydrochloric 
acid,  the  chlorides  converted  into  acetates,  and  the  precipita- 
tion repeated.  Another  method  of  separation  is  to  convert 
the  metals  into  chlorides,  and  ignite  the  dry  chlorides  in  a 
stream  of  hydrogen  gas  :  the  nickel  or  cobalt  is  then  reduced 
to  the  metallic  state,  while  the  chloride  of  zinc  remains  un- 
altered, and  may  be  dissolved  out  by  water.  (For  the  separa- 
tion of  cobalt  from  zinc,  see  also  p.  80.) 

In  precipitating  zinc  from  its  acetic  acid  solution  by  hydro- 
sulphuric acid,  it  is  necessary  that  the  solution  be  quite 
free  from  inorganic  acids,  which  would  interfere  with  the 
precipitation.  This  may  be  effected  either  by  precipitating 
the  metals  with  carbonate  of  soda,  washing  the  precipitate  and 
dissolving  it  in  acetic  acid,  or  by  boiling  the  solution  with 
excess  of  sulphuric  acid  to  drive  off  the  inorganic  acids  (if  vola- 
tile) and  decomposing  the  sulphate  with  acetate  of  baryta. 


SECTION  VI. 

CADMIUM. 

J^Jg.  65-74  or  696-77;  Cd. 

This  metal  is  frequently  found  in  smaU  quantity,  associated 
with  zinc,  and  derives  the  name  cadmium,  applied  to  it  by 
Stromeyer,  from  cadmia  fossilis,  a  denomination  by  which  the 


90  CADMIUM. 

common  ore  of  zinc  was  formerly  desi^ated.  In  the  process 
of  reducing  ores  of  zinc,  the  cadmium  which  they  contain 
comes  over  among  the  first  products  of  distillation,  owing  to 
its  greater  volatility.  It  may  be  separated  from  zinc,  in  an  acid 
solution,  by  hydrosulphuric  acid,  which  throws  down  cadmium 
as  a  yellow  sulphide.  This  sulphide  dissolves  in  concentrated 
hydrochloric  acid,  affording  the  chloride  of  cadmium,  from 
which  the  carbonate  may  be  precipitated  by  an  excess  of  car- 
bonate of  ammonia.  Carbonate  of  cadmium  is  converted  by 
ignition  into  the  oxide ;  and  the  latter  yields  the  metal  when 
mixed  with  one-tenth  of  its  weight  of  pounded  coal,  and  dis- 
tilled in  a  glass  or  porcelain  retort,  at  a  low  red  heat. 

Cadmium  is  a  white  metal,  like  tin,  very  ductile  and  mal- 
leable. It  fuses  considerably  under  a  red  heat,  and  is  nearly 
as  volatile  as  mercury.  The  density  of  cadmium,  cast  in  a 
mould,  is  8*604,  after  being  hammered,  8-6914.  Cadmium 
may  be  dissolved  in  the  more  powerful  acids,  by  substitution 
for  hydrogen,  with  the  aid  of  heat ;  but  nitric  acid  is  its 
proper  solvent. 

Oxide  of  cadmium,  CdO;  6374  or  796'77.— The  only 
known  oxide  of  cadmium  is  obtained  by  the  combustion  of 
the  metal,  or  by  the  ignition  of  its  carbonate,  as  a  powder  of 
an  orange  colour,  or  as  a  white  hydrate  by  precipitation  from 
its  salts  by  an  alkali.  Its  density,  in  the  anhydrous  condition, 
is  8' 183  (Herapath).  By  igniting  the  nitrate,  the  oxide  is 
obtained  in  microscopic  octohedrons,  which  are  dark  bluish 
black  by  reflected,  and  dark  brown  with  a  tinge  of  violet  by 
transmitted  light  (Schuler).  This  oxide  is  soluble  in  am- 
monia, but  not  in  its  carbonate  (differing  in  the  last  property 
from  zinc  and  copper)  nor  in  the  fixed  alkalies.  Its  salts  are 
white,  and  greatly  resemble  those  of  zinc.  They  are  precipi- 
tated of  a  fine  yellow  colour  by  hydrosulphuric  acid. 

Sulphide  of  cadmium  is  distinguished  from  sulphide  of 
arsenic,  which  it  resembles  in  colour,  by  being  insoluble  in 
potash  and  in  sulphide  of  ammonium,  and  by  sustaining  a  red 


SALTS    OF    CADMIUM.  91 

heat  without  subliming.  A  crystalline  sulphide  is  obtained 
by  fusing  1  part  of  the  precipitated  sulphide  with  5  parts  of 
carbonate  of  potash  and  5  parts  of  sulphur;  or  by  passing 
dry  hydrosulphuric  acid  gas  over  strongly-heated  chloride  of 
cadmium. 

Chloride  of  cadmium  forms  a  crystalline  hydrate,  containing 
CdCl  +  2H0.  It  also  forms  crystalline  compounds  with  the 
chlorides  of  ammonium,  potassium_,  sodium,  barium,  stron- 
tium, calcium,  magnesium,  manganese,  iron,  cobalt,  nickeb 
and  copper.  A  solution  of  chloride  of  cadmium,  mixed  with 
excess  of  ammonia,  yields  by  spontaneous  evaporation  the 
compound  NH2CdCl  (C.  v.  Hauer). 

The  same  ammoniacal  solution  treated  with  excess  of  hydro- 
chloric acid  deposits  crystalline  crusts,  which,  according  to 

Sclmler,  contain  CdCl.SNHg  or  NH(NHJ^.C1.  Sul- 
phurous acid  gas  passed  through  the  ammoniacal  solution 
throws  down  a  white  crystalline  precipitate  containing 
CdO.SO24-NH4O.SO2  (Schiller). 

Iodide  of  cadmium  forms  a  crystalline  compound  with  water. 

Bromide  of  cadmium  mixed  in  equivalent  quantity  with 
bromide  of  potassium  in  solution,  yields  crystals,  first  of 
2CdBr.KBr  +  2H0,  afterwards  of  CdBr.2KBr  (C.v.  Hauer). 

Sulphate  of  cadmium  forms  efflorescent  crystals  contain- 
ing CdO.SOg  +  4H0  (Stromeyer).  According  to  Kiihn  and 
Von  Hauer,  an  acid  solution  of  the  salt  concentrated  at 
the  boiling  heat,  deposits  nodular  crystals,  which  contain 
CdO.SOs  +  HO,  and  give  oiF  their  water  at  212°.  The  crys- 
tals obtained  by  evaporation  at  ordinary  temperatures  contain 
3(CdO.S03)+ 8H0,  give  off  nearly  3  eq.  water  at  212°, 
and  the  rest  at  a  low  red  heat  (C.  v.  Hauer).  Sulphate  of  cad- 
mium forms  with  sulphate  of  potash  the  compound  CdO.SOg 
+  KO.SO3  +  6H0,  and  similar  double  salts  with  the  sul- 
phates of  soda  and  ammonia. 

Several  definite  alloys  of  cadmium  have  been  formed.  At  a 
red  heat,  100  parts  of  platinum  retain  1 1 7'3  parts  of  cadmium. 


92  COTPER. 

giving  a  compound  =  CdgPt :  100  parts  of  copper  retain,  at  a 
red  heat,  82'2  of  cadmium,  which  approaches  nearly  to  the  pro- 
portion of  CdCug.  Cadmium  forms  an  amalgam  with  mer- 
cury, which  crystallises  in  octohedrons,  and  consists  of  21 '74 
parts  of  cadmium,  and  78*26  of  mercury.  Cor  dHgg. 

Estimation  of  cadmium,  and  method  of  separating  it  from 
the  preceding  metals.  —  Cadmium  is  best  precipitated  from  its 
solutions  by  carbonate  of  soda ;  it  is  thereby  obtained  as  a 
carbonate,  which  by  ignition  yields  the  brown  oxide  containing 
87*45  per  cent,  of  the  metal. 

From  all  the  preceding  metals  cadmium  may  be  separated 
by  hydrosulphuric  acid ;  the  sulphide  of  cadmium  being  then 
dissolved  by  nitric  acid,  and  the  metal  precipitated  by  carbonate 
of  soda  as  above. 


SECTION    VII. 

COPPER. 

Eg.  31*66  or  395*7;   Cu  {aiprum). 

Copper,  if  not  the  most  abundant,  is  certainly  one  of  the 
most  generally  diffused  of  the  metals.  Its  ores  arc  often 
accompanied  by  metallic  copper,  crystallised  in  cubes  or  octo- 
hedrons. Very  large  masses  of  native  copper  have  been  found 
near  Lake  Superior  in  North  America,  one  of  which  w^eighed 
2200  pounds ;  in  the  Cliff  mine,  on  the  Eagle  river,  a  mass 
has  been  found  weighing  50  tons.  Native  copper  is  also 
found  in  considerable  quantities  in  the  decomposed  basalt  of 
Rheinbreitenbach,  near  Recsk  in  Hungaiy,  and  near  Harlech, 
North  Wales.  The  richest  mines  of  this  country  are  those 
in  Cornwall  and  Anglesea.  The  common  ore  of  this  metal  is 
copper  pyrites,  a  compound  of  subsulphide  of  copper  and  ses- 
quisulphide  of  iron,  or  a  sulphui'-salt,  CuS  -f  FcgSg,  but  in 


COPPER.  93 

which  the  two  sulphides  are  also  found  in  other  proportions, 
and  which  often  contains  an  admixture  of  the  bisulphide  of 
iron.  Few  metallurgic  processes  require  more  skill  and  atten- 
tion than  the  extraction  of  copper  from  this  ore.  The  ore  is 
first  roasted  at  a  high  temperature  in  a  reverberatory  or  flame- 
furnace  (Fig.  7.) J  whereby  the  sulphide  of  iron  is  in  great  part 

Fig.  7. 


converted  into  oxide^  while  the  sulphide  of  copper  remains  un- 
altered. The  product  of  this  operation  is  then  strongly  heated 
with  silicious  sand_,  which  combines  with  the  oxide  of  iron,  form- 
ing a  fusible  slag,  and  separates  from  the  heavier  copper  com- 
pound. This  operation  is  performed  in  a  reverberatory  furnace 
similar  to  the  former,  but  of  smaller  dimensions.  These  pro- 
cesses are  several  times  repeated,  whereby  the  quantity  of  iron 
is  continually  diminished,  and  the  sulphide  of  copper  begins  to 
decompose,  giving  it  up  its  sulphur  and  absorbing  oxygen ;  the 
temperature  is  then  raised  high  enough  to  reduce  the  resulting 
oxide  by  the  aid  of  carbonaceous  matter.  The  coarse  copper 
thus  obtained,  containing  from  80  to  90  per  cent,  of  copper, 
is  then  melted  under  the  action  of  a  strong  blast  of  air, 
to  complete  the  expulsion  of  volatile  matter,  and  the  copper 
is  partially  oxidised.  Lastly,  to  free  it  from  oxide,  which 
renders  it  brittle,  it  is  again  melted  with  its  surface  well 
covered  with  charcoal,  and  a  pole  of  birchwood  is  thrust  into 
it ;  this  causes  considerable  ebullition,  the  oxide  being  reduced 


94  COPPER. 

by  the  carbonaceous  matter,  and  carbonic  acid  escaping. 
Samples  of  the  metal  are  taken  out  from  time  to  time,  and 
tested  by  the  hammer,  the  process  being  discontinued  as 
soon  as  the  right  degree  of  toughness  is  attained.  If  the 
poling  is  continued  too  long,  the  copper  takes  up  carbon,  and 
then  becomes  even  more  brittle  than  in  its  former  oxidised 
state :  it  is  then  said  to  be  over-poled,  and  must  be  again 
melted  in  contact  with  the  air  to  bum  away  the  carbon.* 

Copper  is  the  only  metal  of  a  red  colour.  The  crystals  of 
native  copper,  and  of  that  obtained  in  the  humid  way  by  pre- 
cipitation with  iron,  belong  to  the  regidar  system ;  but  the 
crystals  which  form  in  the  cooling  of  melted  copper  were 
found  by  Seebeck  to  be  rhomboidal,  and  to  have  a  different 
place  in  the  thermo-electric  series  from  the  other  crystals. 
The  density  of  copper  when  cast  is  about  8*83,  and  when 
laminated  or  forged  8*95  (Berzelius).  It  is  less  fusible  than 
silver,  but  more  so  than  gold,  its  point  of  fusion  being  1996° 
(Daniell) .  It  is  one  of  the  most  highly  malleable  metals,  and 
in  tenacity  is  inferior  only  to  iron.  It  has  much  less  affinity 
for  oxygen  than  iron,  and  decomposes  water  only  at  a  bright 
red  heat,  and  to  a  small  extent.  In  damp  air,  it  acquires  a 
green  coating  of  subcarbonate  of  copper,  and  its  oxidation  is 
remarkably  promoted  by  the  presence  of  acids.  The  weaker 
acids,  such  as  acetic,  have  no  effect  upon  copper,  unless  with 
the  concurrence  of  the  oxygen  of  the  air,  when  the  copper 
rapidly  combines  with  that  oxygen,  and  a  salt  of  the  acid  is 
formed.  Copper  scarcely  decomposes  the  hydratcd  acids  by 
displacing  hydrogen ;  when  boiled  in  hydrochloric  acid,  it  dis- 
engages only  the  smallest  traces  of  that  gas.  But  hydrogen 
does  not  precipitate  metallic  copper  from  solution.  Copper 
acts  violently  on  nitric  acid,  occasioning  its  decomposition, 
with  evolution  of  nitric  oxide,  and  dissolving  as  a  nitrate. 

*  A  minute  account  of  the  process  of  copper-smelting  as  practised  at 
Swansea,  lias  lately  been  given  by  Mr.  Napier,  in  the  '*  Philosophical  Maga- 
zine," 1th  Scries,  vols.  iv.  and  v. 


CUPROUS   OXIDE.  95 

Dioxide  of  copper,  Red  oxide  of  copper,  Cuprous  oxide, 
CugO  j  71'32  or  891'4. — This  degree  of  oxidation  is  better 
marked  in  copper  than  in  any  other  metal  of  the  magnesian 
class.  The  dioxide  of  copper  is  found  native  in  octohedral 
crystals,  and  may  be  prepared  artificially  by  heating  to  red- 
ness, in  a  covered  crucible,  a  mixture  of  5  parts  of  the 
black  oxide  of  copper  with  4  parts  of  copper-filings.  It  is 
a  reddish-brown  powder,  which  undergoes  no  change  in  the  air. 
The  surface  of  vessels  of  polished  copper  is  often  converted 
into  red  oxide,  or  bronzed,  to  enable  them  to  resist  the  action 
of  air  and  moisture :  this  is  done  by  covering  them  with  a  paste 
of  sesquioxide  of  iron,  heating  to  a  certain  point,  and  after- 
wards cleaning  them,  to  remove  the  oxide  of  iron ;  or  other- 
wise, by  means  of  a  boiling  solution  of  acetate  of  copper. 

Dilute  acids  decompose  red  oxide  of  copper,  dissolving  the 
protoxide,  and  leaving  metallic  copper.  Undiluted  hydro- 
chloric acid  dissolves  the  red  oxide,  without  decomposition, 
or  rather  forms  a  corresponding  chloride  of  copper,  CU2CI, 
which  is  soluble  in  hydrochloric  acid.  The  hydrated  alkalies 
precipitate  hydrated  cuprous  oxide  from  that  solution,  of  a 
lively  yellow  colom",  which  changes  rapidly  in  air  from  absorp- 
tion of  oxygen. 

Cuprous  oxide  is  also  formed  when  copper  is  placed  in  a 
dilute  solution  of  ammonia  containing  air,  and  is  dissolved  by 
the  alkali.  If  the  ammonia  has  been  corked  up  in  a  bottle 
with  copper  for  some  time,  the  liquid  is  colourless ;  but  on 
pouring  it  out  in  a  thin  stream,  it  immediately  becomes  blue, 
by  absorbing  oxygen.  The  liquid  may  be  again  deprived  of 
colour  by  returning  it  to  the  bottle,  and  closing  it  up,  in  con- 
tact with  the  metal.  Cuprous  oxide  is  also  readily  obtained 
by  the  reducing  action  of  glucose  (grape-sugar)  on  the  prot- 
oxide or  its  salts.  When  a  solution  of  1  part  of  common  sul- 
phate of  copper  and  1  part  of  glucose  is  mixed  with  a  sufficient 
quantity  of  caustic  potash  or  soda  to  redissolve  the  precipitate 
first  formed,  and  the  liquid  gently  warmed,  cuprous  oxide  is 


9G  COPPER. 

abundantly  precipitated  in  the  form  of  a  yellowish-red  crystal- 
line powder.  Cane-sngar  produces  the  same  effects,  but  more 
slowly,  apparently  because  it  must  first  be  converted  into 
glucose. 

Compounds  have  been  obtained  of  cuprous-oxide  with 
several  acids,  particularly  with  sulphurous  acid,  the  sulphite 
forming  a  double  salt  with  sulphite  of  potash,  CU2O.SO2  + 
2(KO.S02)  (Muspratt) ;  also  with  hyposulphurous,  sulphuric, 
carbonic  and  acetic  acids.  When  fused  with  vitreous  matter, 
cuprous  oxide  gives  a  beautiful  ruby-red  glass;  but  it  is 
difficult  to  prevent  the  cuprous  oxide  from  absorbing  oxygen, 
in  which  case  the  glass  becomes  green. 

Hydride  of  copper ,  Cuprous  hydride,  Cu^H.  —  When  a 
solution  of  cupricsulphate  and  hypophosphorous  acid  is  heated 
not  above  158°,  this  compound  is  deposited  as  a  yellow  pre- 
cipitate, which  soon  turns  red-brown.  It  gives  off  hydrogen 
when  heated,  takes  fire  in  chlorine  gas,  and  when  treated  with 
hydrochloric  acid,  is  converted  into  dichloride  of  copper,  with 
evolution  of  a  double  quantity  of  hydrogen,  the  acid  in  fact 
giving  up  its  hydrogen  as  well  as  the  copper-compound 
(Wurtz)  : 

CuJI  +  HCl  =  Cu^Cl  +  HH. 

This  action  is  very  remarkable,  inasmuch  as  metallic  copper 
is  scarcely  acted  upon  by  hydrochloric  acid.  It  appears  to 
arise  from  the  two  atoms  of  hydrogen  contained  in  the  acid 
and  the  hydride  being  in  opposite  states,  the  former  being 
basylous  or  positive,  the  latter  chlorous  or  negative,  and  so 
disposed  to  combine  togetheVy  just  as  the  hydrogen  of  the 
hydrochloric  acid  combines  under  similar  circumstances 
with  the  oxygen  of  the  compound  CU2O.  The  reduction 
of  certain  metallic  oxides  by  peroxide  of  hydrogen  affords 
another  example  of  the  same  kind  of  action. 

Disulphide  of  copper,  Cuprous  sulphide,  CU2S,  forms   the 
mineral  copper -glance,  and   is   also  a  constituent  of  copper 


CUPROUS    SALTS.  97 

pyrites.  It  is  a  powerful  sulphur-base.  Copper-filings,  mixed 
with  half  their  weight  of  sulphur,  unite,  when  heated,  with  in- 
tense ignition,  and  form  this  disulphide. 

Bichloride  of  copper^  Cuprous  chloride,  CU2CI,  may  be  pre- 
pared by  heating  copper-filings  with  twice  their  weight  of 
corrosive  sublimate.  It  was  obtained  by  Mitscherlich  in 
tetrahedrons,  by  dissolving  in  hydrochloric  acid  the  dichloride 
of  copper  formed  on  mixing  solutions  of  the  protochlorides  of 
copper  and  tin,  and  allowing  the  concentrated  solution  to  cool. 
Dichloride  of  cojjper  so  prepared  is  white,  insoluble  in  water, 
soluble  in  hydrochloric  acid,  but  precipitated  by  dilution.  It 
is  dissolved  by  a  boiling  solution  of  chloride  of  potassium, 
and  the  resulting  solution,  if  allowed  to  cool  in  a  close 
vessel,  yields  large  octohedral  crystals  of  a  double  chloride : 
CU2CI.2KCI ;  they  are  anhydrous.  It  is  remarkable  that  the 
forms  of  this  double  salt,  and  of  both  its  constituents,  aU 
belong  to  the  regular  system.* 

When  finely-divided  metallic  copper  is  boiled  in  a  saturated 
solution  of  sal-ammoniac,  ammonia  is  evolved  and  a  white 
salt  formed,  which  crystallises  in  rhombic  dodecahedrons :  it 
contains  NH3.CU2CI,  and  may  be  regarded  as  a  dichloride  of 

copper  and  cuprammonium         ^^   !ci.     A  solution  of  this 

salt  exposed  to  the  air  yields  blue  crystals  of  the  compound 
NH3.Cu2Ci  +  NH3CUCI+HO  ;  and  the  mother-liquor,  after 
further  exposure  to  the  air,  contains  the  salt  NH3.CUCI  + 
NH4CI,  which  at  a  lower  temperature  crystallises  in  large 
cubes  (Ritthausen). 

Diniodide  of  copper,  Cuprous  iodide,  CU2I,  is  a  white  in- 
soluble precipitate,  obtained  on  mixing  a  solution  of  1  part  of 
sulphate  of  copper  and  2-^  parts  of  protosulphate  of  iron,  with 
a  solution  of  iodide  of  potassium. 

Dicyanide  of  copper,  Cuprous  cyanide,  CugCy. — Obtained  as 
a  white  curdy  precipitate   on   adding   hydrocyanic  acid   or 

*  Mitscherlich  in  Poggendorff 's  Annalen,  xlix.  401.,  1840. 
VOL.  II.  H 


98  COPPER. 

cyanide  of  potassium  to  a  solution  of  dichloride  of  copper  in 
hydrochloric  acid,  or  to  a  solution  of  protochloride  of  copper 
mixed  with  sulphurous  acid.  It  forms  a  colomiess  solution 
with  ammonia,  and  a  yellow  solution  with  strong  hydrochloric 
acid,  from  which  it  is  precipitated  by  potash. 

Dicyanide  of  copper  unites  with  the  cyanides  of  the  alkali- 
and  earth-metals,  and  with  the  cyanides  of  manganese,  ii'on, 
zinc,  cadmium,  lead,  tin,  uranium,  and  silver,  forming  double 
salts,  some  of  which  have  the  composition  MCy.Cu2Cy,  others 
SMCy.Cu^Cy  (the  symbol  M  denoting  a  metal). 

CvprosO'Cujjric  cyanide,  CugCy .  CuCy,  is  obtained  as  a 
green  hydrate  by  adding  hydrocyanic  acid  or  cuproso-potassic 
cyanide,  KCy.Cu2Cy,  to  sulphate  of  copper.  It  forms  three 
compounds  with  ammonia,  viz.,  NH3.Cu3Cy2.HO,  obtained 
by  adding  cyanide  of  ammonium  to  a  protosalt  of  copper,  and 
the  compounds  2NH3.Cu3Cy2  and  3NIl3.Cu3Cy2,  formed  by 
the  action  of  ammonia  on  the  first  compound. 

Cuprous  hyj)osiiIj)hite,  CU2O.3S2O2  +  2H0,  separates  in 
microscopic  needles,  having  a  golden  lustre,  on  adding  a 
saturated  solution  of  hyposulphite  of  soda  to  a  concentrated 
solution  of  cupric  sulphite,  till  a  deep  yeUow  colour  is  pro- 
duced. It  dissolves  in  aqueous  sal-ammoniac,  and  the  solu- 
tion deposits  the  compound  CU2O.3S2O2  4-  NHgCuCl  +  HO. 
(C.  v.  Hauer). 

Cuprous  sulphite  is  said  by  some  chemists  to  be  obtained 
in  a  definite  state  by  the  action  of  sulphurous  acid  on  cupric 
oxide ;  but  according  to  Rammelsbcrg  and  Pean  de  St.  Gilles, 
it  exists  only  in  combination  with  cupric  sulphite,  forming  the 
compound  CU2O.SO2  -f  CUO.SO2,  which  crystallises  with 
3  and  5  eq.  of  water, — and  with  the  sulphites  of  the  alkalies. 
By  treating  dichloride  of  copper  with  excess  of  sulphite  of 
ammonia,  prismatic  crystals  are  formed  containing  CU2O.SO2 
+  7(NH40.S02)  +  10  Aq. ;  and  by  saturating  the  solution 
of  this  salt  with  sulphurous  acid,  the  salt  CU2O.S2O2  + 
NH4O.SO3  is  obtained.     A  concentrated  solution  of  sulphite 


CUPRIC    OXIDE.  99 

of  ammonia  and  cupric  sulphate  saturated  with  sulphurous 
acid  gas,  yields  light  green  crystals  containing  fCu20.S02  + 
NH4O  .  SO2)  +  (CU2O  .  SO2  +  CuO  .  SO2)  +  5  aq.  Corre- 
sponding  double  salts  are  formed  by  the  sulphites  of  potash 
and  soda,  but  they  are  very  unstable. 

Protoxide  of  copper ,  Black  oxide  of  copper j  Cupric  oxide,  CuO; 
495*7  or  39*66. — The  base  of  the  ordinary  salts  of  copper,  or 
cupric  salts.  It  is  formed  by  the  oxidation  of  copper  at  a  red  heat, 
but  is  generally  prepared  by  igniting  the  nitrate  of  copper.  It 
is  black  like  charcoal,  and  fuses  at  a  high  temperature.  This 
oxide  is  remarkable  for  the  facility  with  which  it  is  reduced, 
at  a  low  red  heat,  by  hydrogen  and  carbon,  which  it  converts 
into  water  and  carbonic  acid.  It  is  this  property  which  re- 
commends oxide  of  copper  for  the  combustion  of  organic 
substances,  in  close  vessels,  by  which  their  ultimate  analysis 
is  effected. 

Oxide  of  copper  is  a  powerful  base.  Its  salts,  the  cupric 
salts,  are  generally  blue  or  green,  when  hydrated,  but  white 
when  anhydrous.  Although  neutral  in  composition,  they  have 
a  strong  acid  reaction.  They  are  poisonous  ;  but  their  effect 
upon  the  animal  system  is  counteracted  in  some  degree  by 
sugar.  Liquid  albumen  forms  insoluble  compounds  with  these 
salts,  and  is  an  antidote  to  their  poisonous  action.  Copper  is 
separated  in  the  metallic  state  from  its  salts  by  zinc,  iron,  lead, 
and  the  more  oxidable  metals,  which  are  dissolved,  and  take 
the  place  of  the  former  metal. 

Potash  or  soda  added  to  the  solution  of  a  cupric  salt,  throws 
down  at  first  a  blue  precipitate  of  hydrated  cupric  oxide, 
which,  however,  on  agitation,  takes  up  a  portion  of  the  unde- 
composed  salt,  and  forms  with  it  a  green  basic  salt.  An  excess 
of  the  alkali  throws  down  the  hydrated  oxide  in  bulky  blue 
flakes,  which,  on  boiling  the  mixture,  collect  together  in  the 
form  of  a  black  powder,  consisting  of  the  anhydrous  oxide. 
This  reaction  is  greatly  modified  by  the  presence  of  fixed  or- 

H  2 


loo 


COPPER. 


ganic  substances,  such  as  sugar,  tartaric  acid,  &c.  In  a  solu- 
tion of  sulphate  of  copper,  containing  such  substances  in 
sufficient  quantity,  potash  either  produces  no  precipitate,  or 
one  Tvhich  is  quickly  redissolved,  forming  a  blue  solution ;  and 
from  this  solution,  when  boiled,  the  copper  is  sometimes  wholly 
precipitated  as  red  or  yellow  cuprous  oxide,  as  when  grape- 
sugar  is  present, — or  partially,  as  with  cane-sugar,  or  not  at 
all,  as  with  tartaric  acid.  Ammonia,  added  by  degrees,  and 
with  constant  agitation,  to  the  solution  of  a  cupric  salt,  first 
throws  down  a  green  basic  salt,  and  afterwards  the  blue 
hydrate :  an  excess  of  ammonia  dissolves  the  precipitate, 
forming  a  deep  blue  solution.  A  copper  solution  diluted  so 
far  as  to  be  colourless,  becomes  distinctly  blue  on  the  addition 
of  ammonia.  The  blue  colour  thus  produced  is  still  visible, 
according  to  Lassaigne,  in  a  solution  containing  1  part  of  copper 
in  100,000  parts  of  liquid.  Carbonate  of  potash  or  soda  throws 
down,  with  evolution  of  carbonic  acid,  a  greenish  blue  preci- 
pitate of  a  basic  carbonate  of  copper,  which  on  boiling  is 
converted  into  the  black  oxide.  Carbonate  of  ammonia  pro- 
duces the  same  precipitate,  but  when  added  in  excess, 
dissolves  it  abundantly,  forming  a  blue  solution.  Hydro- 
sulphuric  acid  and  solutions  of  alkaline  sulphides  throw  down 
a  brownish  black  precipitate  of  protosulphide  of  copper,  in- 
soluble in  sulphide  of  potassium  or  sodium,  slightly  soluble 
in  sulphide  of  ammonium.  Ferrocyanide  of  potassium  forms 
with  cupric  salts  a  deep  chocolate -coloured  precipitate  of 
ferrocyanide  of  copper.  To  very  dilute  solutions  it  imparts  a 
reddish  colour,  which  is  even  more  delicate  in  its  indications 
than  the  ammonia  reaction,  being  still  visible  in  a  solution 
containing  1  part  of  copper  in  400,000  parts  of  liquid,  according 
to  Lassaigne,  and  in  1,000,000  parts,  according  to  Sarzeau. 
Ferrocyanide  of  copper  dissolves  in  aqueous  ammonia,  and 
reappears  when  the  ammonia  is  evaporated.  This  reaction 
serves  to  detect  extremely  small  quantities  of  copper,  even 
when   associated   with   other   metals.      Thus,  if  a    solution 


CUPIUC    SALTS.  101 

containing  copper  and  iron  be  treated  with  excess  of 
ammonia,  a  few  drops  of  ferrocyanide  of  potassium  added, 
the  liquid  filtered,  and  the  filtrate  left  to  evaporate  in  a  small 
white  porcelain  capsule*,  ferrocyanide  of  copper  will  be  left 
behind,  exhibiting  its  characteristic  red  colour  (Warington). 
Salts  of  copper  impart  a  green  colour  to  flame.  The  black 
oxide  of  copper  dissolves  by  fusion  in  a  vitreous  flux,  and 
produces  a  green  glass.  Any  compound  of  copper  fused  with 
borax  in  the  oxidising  flame  of  the  blowpipe  forms  a  trans- 
parent glass,  which  is  green  while  hot,  but  assumes  a  beautiful 
blue  colour  when  cold.  In  the  reducing  flame,  the  glass 
becomes  opaque,  and  covered  on  the  surface  with  liver-coloured 
streaks  of  cuprous  oxide,  or  metallic  copper.  This  last 
reaction  is  somewhat  difficult  to  obtain^  especially  when  the 
quantity  of  copper  is  small,  but  it  may  always  be  ensured  by 
fusing  a  small  piece  of  metallic  tin  in  the  bead.  Copper  salts 
mixed  with  carbonate  of  soda  or  cyanide  of  potassium,  and 
heated  on  charcoal  before  the  blowpipe,  yield  metallic  copper. 

Thenard  obtained  a  higher  oxide  of  copper,  CuOg,  by  the 
action  of  diluted  bioxide  of  hydrogen  on  the  hydrated  prot. 
oxide  of  copper. 

Chloride  of  copper ,  cupric  chloride,  CuCl,  is  obtained  by 
dissolving  the  black  oxide  in  hydrochloric  acid.  Its  solution 
is  green  when  concentrated,  but  blue  wheu  more  dilute, 
and  the  salt  forms  blue  prismatic  crystals,  containing  two 
atoms  of  water.  It  combines  with  chloride  of  potassium, 
and  more  readily  with  chloride  of  ammonium,  forming  the 
double  salts  KCl.CuCl  +  2H0,  and  NH^Cl.CuCl  +  2H0. 
Another  chloride  of  copper  and  ammonium,  containing 
NH4CI.2CUCI  +  4H0,  is  obtained  in  fine  bluish-green  crys- 
tals, by  mixing  the  solutions  of  1  eq.  sal-ammoniac  and  2  eq. 
chloride  of  copper. 

Chloride  of  copper  likewise  combines  with  ammonia,  form- 
ing the  three  following  compounds: — a.  SNHy.CuCl.  This 
compound   is   obtained   by   saturating   dry  protochloride  of 

H  3 


102  COPPER. 

copper  with  ammoniacal  gas:  it  forms  a  blue  powder. — b.  2NH3. 
CuCl.  Formed  by  passing  ammoniacal  gas  through  a  hot  satu- 
rated solution  of  protochloride  of  copper,  till  the  precipitate 
first  formed  is  completely  redissolved.  During  this  process, 
the  liquid  is  kept  almost  boiling  by  the  heat  developed  by  the 
absorption  of  the  gas;  and  the  resulting  solution  yields,  on 
cooling,  small  dark  blue  octohedrons  and  square  prisms  yni\\ 
four-sided  summits. — c.  NHg.CuCl.  Obtained  by  heating  a  or 
b  to  300°,  or  by  saturating  dry  chloride  of  copper,  at  a  high 
temperature,  with  ammoniacal  gas.  Forms  a  green  powder. 
The  compound  c  may  also  be  regarded  as  chloride  of  citprammo- 
nium,  NH3CU.CI,  or  hydrochlorate  of  cupr amine ,  NHjCu.HCl, 
the  base  being  ammonium  or  ammonia  in  which  1 II  is  replaced 
by  Cu.  Similarly,  b  may  be  regarded  as  a  basic  hijdrochhrate 
of  dicupr amine,  NjHgCu.HCl,  the  base  being  formed  by  the 
union  of  two  atoms  of  ammonia  into  one,  and  the  substitution 
therein  of  ICu  for  IH.  Lastly,  a  may  be  regarded  as  basic 
hydrochlorate  of  tricupramine,  NgHgCu.HCl ;  or  again,  a  may 

be  regarded  as  NHAm2Cu.Cl,  and  b  as  NH2AmCu.Cl. 

Carbonates  of  copper. — When  a  salt  of  copper  is  precipitated 
by  an  alkaline  carbonate,  a  hydrated  subcarbonate  is  produced 
containing  2  eq.  of  oxide  of  copper  to  1  cq.  carbonic  acid.  It 
is  a  pale  blue  bulky  precipitate,  which  becomes  denser  and 
green  when  treated  with  boiling  water.  It  is  used  as  a  pig- 
ment, and  known  as  mineral  green.  The  beautiful  native 
green  carbonate  of  copper,  malachite,  is  of  the  same  composi- 
tion, CUO.CO2  +  CuO.HO.  The  finely  crystallised  blue  copper 
ore  is  another  subcarbonate.  It  may  be  represented  as  the 
neutral  hydrated  carbonate  of  copper,  in  combination  with  a 
similar  carbonate  of  copper,  in  which  the  constitutional  water 
is  replaced  by  oxide  of  copper : 

CCuO.COa  +  HO. 
^CuO.C02  +  CuO. 

In  the  green  carbonate,  the  constitutional  water  of  the  neutral 


CUPRTC    SALTS.  103 

carbonate  of  copper  is  replaced  by  hydrate  of  copper.  The 
neutral  carbonate  of  copper  itself,  of  which  the  formula  would 
be  CuO.COg  +  HO,  is  unknown.  According  to  Thomson*,  the 
anhydrous  subcarbonate  2CuO  .  CO2,  occurs  in  the  form  of 
mysorinej  which  contains  also  ferric  oxide  and  silica. 

Sulphate  of  copper,  Cupric  sulphate,  Blue  vitriol,  CUO.SO3. 
HO  +  4H0;  79-66  or  995*7  +  562-5.— This  salt  may  be 
formed  by  dissolving  copper  in  sulphuric  acid  diluted  with 
half  its  bulk  of  water,  with  ebullition;  the  metal  is  then 
oxidated  with  formation  of  sulphurous  acid.  But  the  sul- 
phate of  copper  is  more  generally  prepared,  on  the  large  scale, 
by  the  roasting  and  oxidation  of  sulphide  of  copper;  or 
by  dissolving  in  sulphuric  acid  the  oxide  formed  by  exposing 
sheets  of  metallic  copper  to  air  at  a  red  heat.  It  forms 
large  rhombo'idal  crystals  of  a  sapphire-blue  colour,  contain- 
ing 5  eq.  of  water,  which  lose  their  transparency  in  dry  air : 
they  are  soluble  in  four  times  their  weight  of  cold,  and  twice 
their  weight  of  boiling  water.  Like  the  other  soluble  salts  of 
copper,  the  sulphate  has  an  acid  reaction;  it  is  used  as  an 
escharotic.  The  water  in  this  salt  may  be  reduced  to  1  eq.  at 
212°;  above  400°  the  salt  is  anhydrous  and  white.  Although 
sulphate  of  copper  does  not  crystallise  alone  with  7  HO,  yet, 
when  mixed  with  the  sulphates  of  magnesia,  zinc,  nickel,  and 
iron,  it  crystallises  along  with  these  isomorphous  salts  in  the 
form  of  sulphate  of  iron.  At  a  strong  red  heat  it  melts  and 
loses  acid. 

The  anhydrous  sulphate  absorbs  2J  eq.  of  ammonia,  and 
forms  a  light  powder  of  a  deep  blue  colour  (H  Rose).  When 
ammonia  is  added  to  a  solution  of  sulphate  of  copper,  an  in- 
soluble subsulphate  is  first  thrown  down,  which  is  redissolved  as 
the  addition  of  ammonia  is  continued,  and  the  usual  deep  azure- 
blue  ammoniacal  solution  formed.  The  ammoniacal  sulphate 
may  be  obtained  in  beautiful  indigo-blue  crystals,  by  passing 

•  Outlines  of  Mineralogy. 

n  4 


lOl  corpteii. 

a  stream  of  ammoniacal  gas  into  a  saturated  liot  solution  of 
tlie  sulphate:  it  is  CuO.S03.HO  +  2^H3  (Berzelius).  These 
crystals  lose  1  eq.  ammonia  and  1  eq.  water  at  390°  (Kane), 
and  are  converted  into  a  green  powder,  CuO.SOg  +  NH3,  or 
(NHgCuO) .  SO3 ;  by  the  cautious  application  of  a  heat  not 
exceeding  500°,  the  whole  of  the  ammonia  may  be  got  rid 
of,  and  sulphate  of  copper  quite  pure  remains  behind.  Sul- 
phate of  copper  forms  the  usual  double  salts  with  sulphate  of 
potash  and  with  sulphate  of  ammonia.  A  saturated  hot 
solution  of  the  double  sulphate  of  copper  and  potash  allows  a 
remarkable  double  subsalt  to  precipitate  in  crystalline  grains, 
KO.S03  +  3(CuO.S03)  4-  CuO.HO  +  3HO.  A  corresponding 
seleniate  is  deposited,  below  the  boiling  point,  and  always  in 
crystals.  The  ammoniacal  and  double  salts  of  sulphate  of 
copper  may  be  represented  thus  : — 

Sulphate  of  copper  (blue  vitriol)    .     .     .  CuO.SOa.HO  +  4II0 
Sulpliate  of  copper  and  potash  ....  CuO.S03,(KO.S03)  +  6H0 
Ilydrated  ammoniacal  sulphate  of  copper  CuO.S03,HO +  2NH3 

Preceding  salt  dried  at  300^ (NH3.CuO).S03 

Rose's  ammoniacal  sulphate CUO.SO3+ (Nn3CuO)S03  +  4NIl3 

Do.  heated  to  350° CUO.SO3  + (NH3CuO)S03 

The  hydrated  ammoniacal  sulphate  may  also  be  regarded 
as  NH2(NHJCu.S04  j   and  Rosens  ammoniacal  sulphate  as 

^^^^-  Uso,. 

NHlNHJ^Cu  ) 

Several  subsiilphates  of  copper  have  been  formed.  By 
digesting  hydrated  oxide  of  copper  in  a  solution  of  sulphate  of 
copper,  a  green  powder  is  obtained,  of  which  the  constituents 
are,  according  to  Berzelius,  3CUO.SO3  +  3H0.  The  bhiish- 
green  precipitate  which  falls  when  ammonia  is  added  to  sul- 
phate of  copper,  or  potash  added  in  moderate  quantity  to 
the  same  salt,  contains,  according  to  Kane^s  and  Graham^s 
analyses  4CUO.SO3  -f  4H0.  By  a  larger  quantity  of  potash, 
Kane  precipitated  a  clear  grass-green  subsulphate,  containing 


CUPRIC    SALTS.  105 

SCaO.SOg-f  12H0.     The  last  subsulpliate  loses  exactly  half 
its  water  at  300^*  ] 

Nitrate  of  copper,  CuO.NOg  4-  3 HO,  is  formed  by  dissolving 
copper  in  nitric  acid.  It  crystallises  from  a  strong  solution 
in  blue  prisms  which  contain  3  atoms  of  water,  or  in  rhom- 
boidal  plates  which  contain  6  atoms  of  water.  This  salt  acts 
upon  granulated  tin,  with  nearly  as  much  energy  as  hydrated 
nitric  acid.  A  crystallised  ammoniacal  nitrate  of  copper  is 
obtained  by  conducting  a  stream  of  ammoniacal  gas  into  a 
saturated  solution  of  nitrate  of  copper.  It  is  anhydrous,  and 
contains  NOg.CuO  +  2NH3  (Kane).     It  may  be  regarded  as 


NH^lNHJCu.NOg. 

Subnitrate  of  copper,  CuO.NOg  +  3(CuO .  HO),  according 
to  the  analyses  of  Gerhardt,  Gladstone-f,  and  Kuhnf,  is  a 
green  powder,  produced  by  the  action  of  heat  upon  the 
neutral  nitrate,  at  any  temperature  between  160°  and  600° ; 
or  by  adding  to  that  salt  a  quantity  of  alkali  insufficient  for 
complete  precipitation.  When  oxide  of  copper  is  drenched 
with  the  most  concentrated  nitric  acid  (HO.NO5),  ^^  ^^  ^^^^^ 
subsalt,  singular  as  it  may  appear,  which  is  formed,  even 
when  the  acid  is  in  great  excess. 

Oxalate  of  copper  and  potash  is  obtained  by  dissolving 
oxide  of  copper  in  binoxalate  of  potash ;  it  crystallises  with 
2  and  with  4  eq.  of  water. 

Acetates  of  copper. — The  neutral  acetate,  CuO.(C^H303)  + 
HO,  or  C^H^CuO*  +  HO,  is  obtained  by  dissolving  oxide  of 
copper  in  acetic  acid.  It  forms  fine  crystals  of  a  deep  green 
colour,  containing  1  eq.  of  water,  which  lose  their  trans- 
parency in  air,  and  are  soluble  in  5  times  their  weight  of 
boiling  water.  This  salt,  when  it  separates  from  an  acid 
solution  below  40°,  also  forms  blue  crystals  containing  5 HO 

*  Transactions  of  the  Eoyal  Irish  Academy,  vol.  xix.  p.  1. ;  or  Ann.  Ch. 
Phys.  t.  Ixxii.  p.  272. 

t  Chem.  Soc.  Mem.  iii.  480.  %  Arch.  Pliarm.  [2.],  1.  283. 


lOG  COPPER. 

(Wohler).  The  green  salt  is  found  in  commerce  under  the 
improper  name  of  distilled  verdigris.  The  acetates  of  copper 
and  potash  unite  in  single  equivalents,  and  form  a  double  salt 
in  fine  blue  crystals,  containing  8H0.  Verdigris  is  a  sub- 
acetate  of  copper,  formed  by  placing  plates  of  the  metal 
in  contact  with  the  fermenting  marc  of  the  grape,  or 
with  cloth  dipped  in  vinegar.  The  bluer  species,  which  con- 
sists of  minute  crystalline  plates,  is  a  definite  compound  of 
1  eq.  acetic  acid,  2  cq.  oxide  of  copper,  and  6  eq.  of  water, 
C^IIaCuO^.C^^O  +  6H0.  The  ordinary  green  species  is  a 
mixture  of  the  sesqui-  and  tribasic  acetates  of  copper,  with  the 
preceding  bibasic  acetate.  Water  dissolves  out  from  verdigris 
the  sesquibasic  acetate^  which  presents  itself  on  evaporating 
the  solution,  sometimes  as  an  amorphous  mass,  and  some- 
times in  crystalline  grains  of  a  pale  blue  colour.  The  sesqui- 
basic acetate  consists  of  2  eq.  of  acetic  acid,  3  eq.  of  oxide  of 
copper,  and  G  eq.  of  water;  it  loses  3  cq.  of  water  at  212°. 
The  tribasic  acetate  is  the  insoluble  residue  which  remains 
after  the  lixiviation  of  verdigris.  It  is  a  clear  green  powder, 
which  loses  nothing  at  212^.  It  contains  2  cq.  of  acetic  acid, 
6  eq.  oxide  of  copper,  and  3  cq.  of  water  (Berzclius). 

Acetate  of  copper  also  combines  with  acetate  of  lime,  and 
"with  several  other  salts.  The  double  acetate  and  arsenite  of 
copper  is  a  crystalline  powder  of  a  brilliant  sea-green  colour, 
which  is  used  as  a  pigment,  under  the  name  of  Schweinfurt 
green.  It  is  obtained  by  mixing  boiling  solutions  of  equal 
parts  of  arsenious  acid  and  neutral  acetate  of  copper,  adding 
to  the  mixture  its  own  volume  of  cold  water,  and  leaving  the 
whole  at  rest  for  several  days.  It  is  a  highly  poisonous  sul)- 
stance.  From  the  analysis  of  Ehrmann,  its  formula  is 
CJI,CuO^  +  3(CuO.As03). 

The  most  important  alloys  of  copper  are  those  which  it 
forms  with  tin  and  zinc  : 

100  parts  of  copper  with  5  tin   (or  4  tin   +1  zinc)  form 
the  bronze  used  for  coin. 


ESTIMATION    OP   COPPER.  107 

100  parts  copper  with  10  tin,  form  bronze  and  gun-metal. 
100  parts  copper  with  20  to  25  tin,  form  bell-metal. 
100  parts  copper  with  30  to  35  tin,  form  speculum-metal. 

A  little  arsenic  is  generally  added  to  the  last  alloy,  to  increase 
its  whiteness. 

The  different  varieties  of  brass  are  prepared,  either  by  fusing 
together  the  two  metals,  copper  and  zinc,  or  by  heating  cop- 
per under  a  mixture  of  charcoal  and  calamine — an  operation  in 
which  zinc  is  reduced  and  its  vapour  absorbed  by  the  copper. 
Two  or  three  parts  of  copper  to  one  of  zinc  form  common 
brass.  The  brass  known  as  Muntz^s  white  metal,  which  re- 
sists the  solvent  action  of  sea-water  much  better  than  pure 
copper,  and  is,  in  consequence  largely  used  for  the  sheathing 
of  ships,  consists  of  60  parts  copper  to  40  parts  zinc,  and 
appeai-s  to  be  the  atomic  compound  Ca2Zn.  Equal  parts  of 
copper  and  zinc,  or  four  of  the  former  and  one  of  the  latter, 
give  an  alloy  of  a  higher  coloui*,  resembling  gold,  and  on  that 
account  called  similor. 


ESTIMATION    OF    COPPER,  AND    METHODS   OP   SEPARATING   IT 
PROM    OTHER    METALS. 

Copper  is  best  precipitated  by  caustic  potash,  which  when 
added  to  a  boUing  solution  of  a  cupric  salt,  throws  down  the 
protoxide  of  copper  in  the  form  of  a  heavy  black  powder. 
From  tliis  precipitate  every  trace  of  potash  may  be  removed 
by  washing  with  hot  water ;  and  the  washed  precipitate  may 
then  be  dried  and  ignited  in  a  platinum  or  porcelain  crucible. 
It  must  be  weighed  immediately  after  cooling,  with  the  cover 
on  the  crucible,  because  it  absorbs  moisture  rapidly  firom  the 
air.     It  contains  79*82  per  cent,  of  copper  (H.  Rose). 

Copper  is  often  precipitated  from  its  solutions  by  hydro- 
sulphuric  acid.  In  that  case  the  precipitated  sulphide  must 
be  washed  as  quickly  as  possible  with  water  containing  hy- 
drosulphuric  acid,  to  prevent  oxidation ;  the  precipitate  mav 


108  COPPER. 

then  be  dried,  and  the  filter  burnt  with  the  precipitate  on  it, 
in  a  porcelain  basin ;  after  which  the  precipitate  is  treated 
with  concentrated  nitric  acid,  which  dissolves  it,  with  separa- 
tion of  sulphur,  and  the  copper  precipitated  from  the  filtered 
solution  by  potash  as  above.  The  chief  precaution  to  be 
attended  to  in  this  process  is  to  wash  the  precipitated  sulphide 
quickly,  and  to  preserve  it  as  completely  as  possible  from 
contact  with  the  air;  otherwise  the  sulphide  becomes  par- 
tially oxidised  and  converted  into  sulphate,  which  being  soluble, 
runs  through  the  filter ;  when  this  takes  place,  the  filtrate 
becomes  brown,  because  the  copper  thus  carried  through,  is 
again  precipitated  by  hydrosulphuric  acid. 

Volumetric  methods. — Copper  may  be  volumetrically  deter- 
mined by  means  of  a  solution  of  permanganate  of  potash,  by  a 
process  founded  on  that  adopted  by  Margueritte  for  the  deter- 
mination of  iron  (p.  56.).  The  copper  compound  having  been 
weighed  and  dissolved  in  acid,  is  mixed  in  a  porcelain  basin, 
with  neutral  tartrate  of  potash  and  excess  of  caustic  potash,  and 
then  heated  with  a  quantity  of  milk-sugar,  or  honey,  sufficient 
to  precipitate  all  the  copper  as  cuprous  oxide,  the  completion 
of  the  precipitation  being  indicated  by  the  brown  colour  which 
the  liquid  then  acquires.  The  precipitated  cuprous  oxide  is  then 
filtered,  washed  with  hot  water,  and  gently  heated,  together 
with  the  filter,  with  a  mixture  of  pure  scsquichloride  of  iron  and 
dilute  hydrochloric  acid.  It  is  thereby  dissolved  in  the  form 
of  protochloride  of  copper,  the  scsquichloride  of  iron  being 
at  the  same  time  reduced  to  protocldoride : 

CU2O  +  Fe^Clg  +  HCl = 2CuCH-  2reCl  +  HO. 

In  the  filtered  liquid,  diluted  to  a  convenient  strength  and 
heated  to  about  86°,  the  quantity  of  iron  in  the  state  of  proto- 
chloride is  determined  by  a  graduated  solution  of  permanganate 
of  potash  in  the  manner  already  described  (p.  56.),  and  thence 
the  equivalent  quantity  of  copper  is  readily  determined.  The 
presence  of  lead,   zinc,  bismuth,  manganese,  or  iron,  in  the 


ESTIMATION    OF   COPPER.  109 

alkaline  solution  does  not  interfere  with  the  process ;  silver  or 
mercury  must  be  separated  before  the  precipitation  of  the 
cuprous  oxide. 

Another  method,  which  appears  to  give  very  exact  results, 
is  to  treat  the  copper-solution  with  iodide  of  potassium, 
whereby  diniodide  of  copper  is  precipitated  and  iodine  set 
free : 

2(CuO.N05)  +  2KI  =  CU2I  4-  I  +  2(KO.N05), 

and  remove  the  free  iodine  by  means  of  a  standard  solution  of 
hyposulphite  of  soda,  whereby  iodide  of  sodium  and  tetrathio- 
nate  of  soda  are  produced  : 

2(NaO.S202)  +  I  =  Nal  +  KaCS^Og. 

The  copper- compound,  if  solid,  an  alloy  for  example,  is 
dissolved  in  nitric  acid  j  carbonate  of  soda  added  till  a  slight 
precipitate  is  formed;  and  this  precipitate  redissolved  in  acetic 
acid  (free  nitric  acid  would  vitiate  the  result  by  decomposing 
the  iodide  of  potassium) .  A  quantity  of  iodide  of  potassium 
is  next  added,  equal  to  at  least  six  times  the  weight  of  the 
copper  to  be  determined,  and  then  the  standard  solution  of 
hyposulphite  of  soda,  in  sufficient  quantity  to  remove  the 
greater  part  of  the  free  iodine,  which  point  will  be  indicated 
by  the  colour  of  the  liquid  changing  from  brown  to  yellow. 
Lastly,  a  clear  solution  of  starch  is  added,  and  the  addition  of 
the  hyposulphite  of  soda  cautiously  continued  till  the  blue 
colour  of  the  iodide  of  starch  is  completely  destroyed.  The 
solution  of  hyposulphite  of  soda  is  graduated  by  dissolving  a 
known  weight  of  pui-e  electrotype  copper  in  nitric  acid,  and 
proceeding  as  above.  If  the  copper-compound  contains  a  large 
quantity  of  lead  or  iron,  these  metals  must  be  removed  before 
commencing  the  determination,  because  the  yellow  colour  of 
the  iodide  of  lead  and  the  red  of  the  acetate  of  iron  might 
interfere  with  the  result  (E.  O.  Brown).* 

*  In  a  paper  read  before  the  Cliemical  Society,  Nor  17th,  1856,  and  to  be 
Published  in  the  10th  Yolumc  of  the  Society's  Journal. 


110  COPPER. 

Pelouze's  method,  which  consists  in  treating  the  copper 
solution  with  excess  of  ammonia,  and  precipitating  the  copper 
as  oxysulphide,  CuO.SCuS,  by  adding  a  graduated  solution  of 
sulphide  of  sodium  tiU  the  blue  colour  is  completely  destroyed, 
appears,  from  Mr.  Brown's  experiments,  to  be  liable  to 
uncertainty  from  two  causes  :  first,  because  the  oxysulphide 
of  copper  reduces  a  portion  of  the  protoxide  of  copper  to 
dioxide,  thereby  rendering  the  solution  colourless  before  the 
precipitation  is  complete  ;  and  secondly,  because  a  portion  of 
the  sulphide  of  sodium  is  oxidised  and  converted  into  hyposul- 
phite of  soda. 

Copper  is  separated  from  all  the  preceding  metals,  except 
cadmium,  by  means  of  hydrosulphuric  acid,  the  solution  being 
preWously  acidulated  with  hydrochloric  or  sulphuric  acid. 
When  zinc,  nickel,  or  cobalt  is  present,  a  considerable  excess 
of  acid  must  be  added,  otherwise  a  portion  of  these  metals 
will  be  precipitated  together  with  the  copper. 

From  cadmium^  copper  may  be  separated  by  carbonate  of 
ammonia,  which  dissolves  the  copper  and  leaves  the  cadmium. 
The  deposition  of  the  cadmium  is  not  complete  till  the  liquid 
has  been  exposed  for  some  time  to  the  air.  The  separation  is, 
however,  better  effected  by  adding  to  the  solution  of  the  two 
metals  a  quantity  of  cyanide  of  potassium,  sufficient  to  rc- 
dissolve  the  precipitate  first  formed,  and  then  passing  hydro- 
sulphuric  acid  through  the  solution.  Sulphide  of  cadium 
is  then  precipitated,  and  on  driving  off  the  excess  of 
hydrosulphuric  acid  by  heat,  and  adding  more  cyanide  of 
potassium,  the  sulphide  of  copper  remains  completely  dis- 
solved. The  copper  may  be  precipitated  as  sulphide  by 
mixing  the  filtrate  with  hydrochloric  acid :  but  it  is  better  to 
boil  the  filtrate  with  aqua-regia,  till  all  the  hydrocyanic  acid  is 
expelled,  and  then  precipitate  the  copper  by  potash  (Haidlen 
and  Fresenius). 


LEAD.  Ill 


SECTION    VIII. 

LEAD. 

Eq,  103-56  or  1294-5;  Pb  [jMmbum). 

Lead  was  one  of  tlie  earliest  known  of  the  metals.  A  con- 
siderable number  of  its  compounds  are  found  in  nature,,  but 
the  sulphide,  or  galena,  is  the  only  one  which  is  important  as 
an  ore  of  lead.  The  reduction  of  the  metal  is  effected  by 
heating  the  sulphide  with  exposure  to  air  (or  roasting),  by 
which  much  of  the  sulphur  is  burned  and  escapes  as  sulphu- 
rous acid,  and  a  fusible  mixture  of  oxide  of  lead  and  sulphate 
of  lead  is  produced.  A  fresh  portion  of  the  ore  is  added,  which 
reacts  upon  the  oxide  of  lead,  the  sulphur  and  oxygen  forming 
sulphurous  acid,  and  the  lead  of  both  oxide  and  sulphide 
being  consequently  reduced.  Lime  also  is  added,  which  de- 
composes the  sulphate  of  lead,  and  exposes  the  oxide  to  be 
reduced  by  the  fuel  or  by  sulphide. 

Lead  has  a  bluish  grey  colour  and  strong  metallic  lustre, 
is  very  malleable,  and  so  soft,  when  it  has  not  been  cooled 
rapidly,  as  to  produce  a  metallic  streak  upon  paper.  Its  density 
is  11*445,  and  is  not  increased  by  hammering.  Its  tenacity 
is  less  than  that  of  any  other  ductile  metal.  The  melting 
point  of  lead  is  612° ;  on  solidifying,  this  metal  shrinks  con- 
siderably, so  that  bullets  cast  in  a  mould  are  never  quite 
round.  Lead,  like  most  other  metals,  assumes  the  octohedral 
form  on  crystallising.  Lead  is  one  of  the  less  oxidable  metals, 
at  least  when  massive ;  its  surface  soon  tarnishes,  and  is  covered 
with  a  grey  pellicle,  which  appears  to  defend  the  metal  from 
further  change.  Rain  or  soft  water  cannot  be  preserved  with 
safety  in  leaden  cisterns,  owing  to  the  rapid  formation  of  a 
white  hydratcd  oxide  at  the  line  where  the  metal  is  exposed 


112  LEAD. 

to  both  air  and  water ;  the  oxide  formed  is  soluble  in  pure 
water,  and  highly  poisonous.  But  a  small  quantity  of  car- 
bonic acid,  which  spring  and  well  ^yater  usually  contain, 
arrests  the  corrosion  of  the  lead,  by  converting  the  oxide  of 
lead  into  an  insoluble  salt,  and  prevents  the  contamination 
of  the  water.*  Lead  is  not  directly  attacked  by  hydrochloric 
and  sulphuric  acids,  at  the  usual  temperature,  but  they  favour 
its  union  with  oxygen  from  the  air.  Its  best  solvent  is  nitric 
acid.  Besides  a  protoxide,  PbO,  which  is  a  powerful  base, 
lead  forms  a  suboxide  Pb20,  and  a  bioxide  PbO^,  wliich  do 
not  combine  with  acids. 

Suboxide  of  lead,  Pb20,  was  discovered  by  Dulong,  and  is 
best  obtained  by  heating  the  oxalate  of  lead  to  low  redness  in 
a  small  retort.  It  is  dark  grey,  almost  black,  and  pulverulent, 
and  is  not  affected  by  metallic  mercury.  According  to  tlie 
analysis  of  Boussingault,  it  contains  1  eq.  of  oxygen  to  2  eq. 
of  lead.  The  grey  pellicle  which  forms  upon  lead  exposed  to 
the  air  is,  according  to  Berzelius,  the  same  suboxide. 

Protoxide  of  lead,  PbO,  111*56  or  1394*5. — When  a  stream 
of  air  is  thrown  upon  the  surface  of  melted  lead,  the  metal  is 
rapidly  converted  into  the  protoxide,  of  a  sulphur-yellow 
colour.  The  oxidated  skimmings  of  the  metal  are,  in  this 
condition,  termed  massicot,  and  were  at  one  time  used  as  a 
yellow  pigment.  This  preparation  is  fused  at  a  bright  red 
heat,  and  the  oxide  is  thus  separated  from  some  metallic  lead, 
with  which  it  is  intermixed  in  massicot.  The  fused  oxide,  on 
solidifying,  forms  a  brick-red  mass,  which  divides  easily  into 
crystalline  scales,  tough  and  not  easily  pulverised ;  they  form 
litharge.  The  protoxide  of  lead  can  be  obtained  distinctly 
crystallised  by  various  processes,  but  always  presents  itself 
in  the  same  form,  an  octohedron  with  a  rhombic  base 
(Mitscherlich).  By  igniting  the  subnitrate  of  lead,  the  prot- 
oxide is  obtained  very  pure,  and  of  a  rich  lemon-yellow  colour. 
Its  density  after  fusion  is  9*4214. 

*  Dr.  Cliristison's  Treatise  on  Poisons. 


PROTOXIDE    OF    LEAD.  113 

When  the  acetate^  or  any  other  salt  of  lead,  is  precipitated 
by  potash,  the  protoxide  falls  as  a  white  hydrate,  which  may 
be  dried  at  212''  without  decomposition.  It  contains  3^ 
per  cent,  water,  and  is,  therefore,  the  hydrate  2PbO  .  HO 
(Mitscherlich).  Oxide  of  lead  likewise  crystallises  anhydrous, 
from  solution,  at  the  usual  temperature,  when  precipitated 
under  such  circumstances  that  it  cannot  find  water  to  com- 
bine with.  This  oxide  dissolves  in  above  12,000  times  its 
weiglit  of  distilled  water,  which  acquires  thereby  an  alkaline 
reaction,  but  not  in  water  containing  any  saline  matter.  It 
is  soluble  in  potash  or  soda ;  and  the  solutions,  when  evapo- 
rated, yield  small  crystals  of  an  alkaline  compound.  A  com- 
pound of  lime  and  oxide  of  lead  is  obtained  in  needles,  when 
hydrate  of  lime  and  that  oxide  are  heated  together,  and  the 
solution  allowed  to  evaporate  with  exclusion  of  air.  This 
solution  has  been  employed  to  dye  the  hair  black.  Oxide  of 
lead  combines  readily  with  the  earths  and  metallic  oxides  by 
fusion,  and  when  added  to  the  materials  of  glass,  imparts  bril- 
liancy to  it  and  increased  fusibility. 

Oxide  of  lead  is  a  powerful  base,  resembling  baryta  and 
strontia,  and  affords  a  class  of  salts  which  often  agree  in  form 
and  in  general  properties  with  the  salts  of  these  earths.  Its 
carbonate  occurs  in  plumbocalcite,  in  the  form  of  carbonate 
of  lime,  an  isomorphism  by  which  the  protoxide  of  lead  is 
connected  with  the  magnesian  oxides.  All  its  soluble  salts 
are  poisonous,  although  no  salt  of  lead,  with  the  exception  of 
the  insoluble  carbonate,  is  highly  so  (Dr.  A.  T.  Thomson). 
In  a  case  of  accidental  poisoning  by  the  carbonate,  acetic  acid 
proved  a  sufficient  antidote. 

Caustic  alkalies  precipitate  lead  from  its  solutions  as  a 
white  hydrate,  soluble  in  potash  and  soda,  insoluble  in  am-  • 
monia.  Alkaline  cirhonates  throw  down  a  white  precipitate 
of  carbonate  of  lead,  insoluble  in  excess  of  the  reagent.  Hy- 
drochloric acid  and  soluble  chlorides  produce  in  moderately 
strong  lead-solutions,  a  white  crystalline  precipitate  of  chloride 

VOL.  ir.  1 


114  LEAP. 

of  lead,  easily  soluble  in  potash,  insoluble  in  ammonia,  soluble 
in  a  considerable  quantity  of  Avater ;  in  dilute  solutions  {e.  y. 
in  a  solution  of  1  part  of  nitrate  of  lead  in  100  parts  of  water) 
no  precipitate  is  formed.  Sulphuric  acid  and  soluble  sulphates 
throw  down,  even  from  very  dilute  solutions,  a  white,  pul- 
verulent precipitate  of  sulphate  of  lead,  easily  soluble  in 
potash,  soluble  also,  though  slowly,  in  hydrochloric  and  nitric 
acid ;  but  by  adding  a  considerable  excess  of  sulphuric  acid, 
lead  may  be  completely  precipitated  even  from  solutions  con- 
taining hydrochloric  or  nitric  acid.  According  to  Lassaigne, 
1  part  of  oxide  of  lead  (in  the  form  of  nitrate)  dissolved  in 
25,000  parts  of  water,  gives  an  opalescence  with  sulphate  of 
soda,  after  a  quarter  of  an  hour.  Hydrosulphuric  acid  and 
alkaline  sulphides  produce  a  black  precipitate  of  sulphide  of 
lead,  insoluble  in  sulphide  of  ammonium.  In  very  dilute 
solutions,  cnly  a  brown  colouring  is  produced,  the  limit  of  the 
reaction  being  attained,  according  to  Lassaigne,  with  1  part 
of  oxide  of  lead  (in  the  form  of  nitrate)  dissolved  in  350,(){)() 
parts  of  water.  If  the  solution  of  the  lead-salt  contains  free 
hydrochloric  acid,  the  precipitate  is  red  or  yellow,  and  a  large 
excess  of  hydrochloric  acid  prevents  it  altogether.  Iodide  of 
potassium  produces  a  bright  yellow  precipitate  of  iodide  of 
lead,  which  dissolves  in  boiling  water  and  separates  again  on 
cooling  in  crystalline  spangles,  exhibiting  a  beautiful  play  of 
colours.  Chromate  and  bichromate  of  potash  throw  down 
yellow  chromate  of  lead,  easily  soluble  in  caustic  potash. 
The  limit  of  this  reaction  is  attained  with  1  part  of  oxide 
of  lead  (in  the  form  of  nitrate)  dissolved  in  70,000  parts  of 
water  (Harting).  Iron  and  zinc  throw  down  metallic  lead. 
If  a  mass  of  zinc  be  suspended  in  a  solution,  made  by  dis- 
solving one  ounce  of  acetate  of  lead  in  two  pounds  of  distilled 
water,  the  lead  is  precipitated  in  beautiful  crystalline  plates, 
which  are  deposited  not  only  in  metallic  contact  with  the  zinc, 
but  extend  from  it  to  a  considerable  distance  in  the  liquid, 
forming  what  is  called  the  lead-tree.     Lead-salts,  mixed  with 


PROTOXIDE    OF    LEAD.  115 

carbonate  of  soda  or  cyanide  of  potassium,  and  ignited  on 
cliarcoal  before  the  blow-pipe,  yield  a  malleable  button  of 
lead.  The  oxides  of  lead  are  reduced  by  simply  heating  them 
with  the  blowpipe  flame  on  charcoal. 

Sesquioxide  of  lead,  Pb203.  —  Hypochlorite  of  soda  throws 
down  from  lead-salts  a  reddish  yellow  mixture  of  sesquioxide 
and  chloride  of  lead.  The  sesquioxide  may  be  obtained  free 
from  chloride  by  supersaturating  a  solution  of  nitrate  of  lead 
with  potash,  in  quantity  sufficient  to  redissolve  the  precipitated 
hydrate,  and  then  treating  it  with  hypochlorite  of  soda.  The 
sesquioxide  is  converted  by  acids  into  bioxide  and  an  ordinary 
salt  of  lead  (Winkelblech). 

Bioxide  or  peroxide  of  lead,  Pb02,  may  be  obtained  in  the 
same  manner  as  the  peroxides  of  cobalt  and  nickel,  by  ex- 
posing the  protoxide  suspended  in  water  to  a  stream  of 
chlorine ;  also  by  fusing  protoxide  of  lead  with  chlorate  of 
potash  at  a  temperature  short  of  redness ;  or  by  digesting  the 
following  intermediate  oxide,  minium,  in  diluted  nitric  acid, 
which  dissolves  the  protoxide  of  lead,  decanting  off  the  nitrate 
of  lead,  and  washing  the  powder  which  remains  with  boiling 
water.  "VVohler  precipitates  a  solution  of  4  parts  of  acetate  of 
lead  with  a  solution  of  3  parts  or  rather  more  of  crystallised 
carbonate  of  soda,  and  passes  chlorine  gas  through  the  result- 
ing thin  pulpy  mass,  till  the  whole  of  the  carbonate  of  lead  is 
converted  into  brown  bioxide,  amounting  to  2i  parts,  which 
may  then  be  washed.  No  chloride  of  lead  is  formed  in  this 
reaction,  the  whole  of  the  chlorine  combining  with  the 
sodium,  while  acetic  and  carbonic  acid  are  set  free.  Bioxide 
of  lead  is  of  a  dark  earthy-brown  colour.  It  loses  half  its 
oxygen  by  ignition;  absorbs  sulphurous  acid  with  great 
avidity,  and  becomes  sulphate  of  lead;  and  affords  chlorine 
when  digested  in  hydrochloric  acid. 

Minium  or  red  lead  is  formed  by  heating  massicot  or  pro- 
toxide of  lead,  which  has  not  been  fused,  to  incipient  redness 
in  a  flat  furnace,  of  a  particular  construction,  and  directing  a 

I  2 


116  LEAD. 

current  of  air  upon  its  surface.  Oxygen  is  absorbed,  and  an 
oxide  formed  of  a  fine  red  colour,  with  a  shade  of  yellow.  It 
is  not  constant  in  composition.  The  proportion  of  oxygen, 
when  the  absorption  is  least  considerable,  approaches  that  of 
a  compound  containing  3PbO.Pb02;  and  such  was  the  com- 
position of  a  crystallised  compound  of  a  fine  red  colour,  formed 
})y  accident  in  a  minium  furnace,  and  analysed  by  Houton- 
Labillardiere.  But  when  the  absorption  is  favoured  by  time 
and  most  considerable,  it  approaches  but  never  exceeds  2*4 
per  cent,  of  the  original  weight  of  the  protoxide.  This  re- 
sult agrees  with  the  formula  Pb304,  and  accordingly  minium 
may  be  regarded  as  a  compound  of  protoxide  and  ])ioxidc  of 
lead  2PbO.Pb02,  or  of  protoxide  and  sesquioxide  PbO.Pb203. 
A  sample  of  minium  analysed  by  Longchamps  contained 
SPbO.PbOg.  The  finest  minium  is  obtained  by  calcining 
oxide  of  lead  from  the  carbonate,  at  about  G00°. 

Minium  is  not  altered  by  being  heated  in  a  solution  of 
acetate  of  lead,  which  is  capable  of  dissolving  free  protoxide  of 
lead.  AY  hen  heated  to  redness,  it  loses  oxygen,  and  leaves 
the  protoxide.  It  does  not  combine  with  acids,  but  is  resolved 
by  a  strong  acid  into  bioxide  of  lead  and  protoxide,  the  latter 
combining  with  the  acid.  When  minium  is  treated  with 
concentrated  acetic  acid,  it  first  becomes  white,  and  then 
dissolves  entirely  in  a  new  quantity  of  acid  without  colouring 
it.  But  the  solution  gradually  decomposes,  and  bioxide  of 
lead  separates  from  it  of  a  blackish- brown  colour  (Berzelius). 

Protosiilphide  of  lead,  PbS,  is  thrown  down  from  salts  of 
lead,  by  hydrosulphui'ic  acid,  as  a  black  precipitate,  which 
is  insoluble  in  diluted  acids  or  in  alkalies.  It  forms  also  the 
ore  galena,  which  crystallises  in  the  cube  and  other  forms  of 
the  regular  system ;  its  density  is  7'585.  Sulphide  of  lead  is 
decomposed  easily  by  nitric  acid,  and  converted  into  nitrate 
and  sulphate  of  lead,  with  separation  of  a  little  sulphur.  The 
more  concentrated  the  nitric  acid,  the  greater  is  the  quantity 
of  sulphate  produced      Recently  precipitated  sulphide  of  lead 


SULPHIDE  Of    LEAD.  117 

may  be  completely  dissolved  in  the  form  of  nitrate  by  boiling 
with  dilute  nitric  acid.  Concentrated  and  boiling  hydro- 
chloric acid  dissolves  sulphide  of  lead,  with  disengagement  of 
hydrosulphuric  acid  gas.  Galena  may  be  united  by  fusion 
with  more  lead,  and  gives  the  subsulphides  Pb4S,  and  PbgS. 
When  a  solution  of  persulphide  of  potassium  is  added  to  a 
salt  of  lead,  a  blood-red  precipitate  appears,  which  is  a  per- 
sulphide of  lead,  but  is  almost  immediately  changed  into  the 
black  protosulphide  of  lead  and  free  sulphur. 

Chloride  of  lead,  PbCl,  139*06  or  1738-25.  — Lead  dissolves 
slowly  in  hydrochloric  acid,  by  substitution  for  hydrogen, 
forming  the  chloride  of  lead,  but  only  when  assisted  by  the 
action  of  the  air.  The  same  compound  is  obtained  by  digest- 
ing oxide  of  lead  in  hydrochloric  acid,  and  also  falls  as  a 
white  precipitate,  when  a  salt  of  lead  is  added  to  any  soluble 
chloride.  The  chloride  of  lead  is  soluble  in  135  times  its 
weight  of  cold  water,  and  more  so  in  hot  water,  from  which  it 
crystallises  on  cooling  in  long  flattened  acicular  crystals,  which 
are  anhydrous.  It  is  very  fusible,  and  may  be  sublimed  at  a 
higher  temperature 

Oxy chloride  of  lead.  —  Chloride  of  lead  combines  in  five 
different  proportions  with  the  protoxide,  forming  the  follow- 
ing compounds  : —  a.  3PbCl.PbO.  Four  parts  of  chloride  of 
lead  ignited  with  1  part  of  litharge  yield  a  fused,  laminar, 
pearl-grey  mixture,  which,  when  triturated  with  water,  swells 
up  to  a  bulky  mass  having  the  above  composition  (Vauquelin). 
The  same  substance  is  obtained  by  Mr.  Pattinson,  by  decom- 
posing carbonate  of  lead  with  lime-water,  and  used  as  a  white 
pigment. — b.  PbCl.PbO.  Formed  by  igniting  chloride  of  lead 
in  contact  with  air  till  it  no  longer  fumes,  or  by  fusing  chlor- 
ide and  carbonate  of  lead  together.  Carbonic  acid  is  then 
set  free,  and  a  compound  formed  which  is  of  a  deep  yellow 
colour  while  fused,  but  as  it  cools  assumes  a  lemon-yellow 
colour,  and  becomes  nacreous  and  crystalline  (Dobereiner). — 
c.  PbC1.2PbO.    This  compound  forms  the  mineral  Mendi^nte, 

I  3 


118  LEAD. 

found  at  Mendip,in  Somersetshire,  where  it  occui's  in  yellowish- 
wliite,  right  rhombic  prisms,  which  are  harder  than  gypsum, 
translucent,  and  have  an  adamantine  lustre  (Berzelius).  It 
also  occurs,  and  in  a  state  of  greater  purity,  at  Brilon,  near 
Stadtbergen,  in  Westphalia ;  the  crystals  there  found  are  white, 
translucent,  and  have  a  mother-of-pearl  lustre  on  the  cleavage 
surfaces.*  —  d.  PbCl.SPbO. '  Obtained  by  fusing  1  eq.  chlor- 
ide of  lead  with  3  eq.  of  the  protoxide  ;  also  in  the  hydrated 
state,  PbC1.3PbO  +  HO  or  4PbO.HCl,  by  decomposing  chlor- 
ide of  lead  with  ammonia;  by  precipitating  subacetate  of 
lead  with  common  salt ;  and  by  decomposing  a  solution  of 
common  salt  with  protoxide  of  lead.  The  hydrate  is  a  white 
flocculent  mass,  and  when  fused  yields  the  anhydrous  com- 
pound, which  is  a  greenish  yellow  laminated  mass,  forming  a 
yellow  powder.  —  e.  PbC1.5PbO.  Obtained  by  fusing  1  eq. 
chloride  of  lead  with  5  cq.  of  the  protoxide.  Orange-yellow 
substance,  yielding  a  deep  yellow  powder. — /.  PbC1.7PbO,  is 
produced  on  fusing  by  heat  a  mixture  of  10  parts  of  pure 
oxide  of  lead  and  1  part  of  pui'e  sal-ammoniac,  a  portion  of 
the  lead  being  at  the  same  time  reduced.  The  surbasic 
chloride  when  fused  affords  cubic  crystals  on  cooling  slowly. 
It  forms  in  that  state  a  beautiful  yellow  pigment,  known  as 
Turner's  yellow  in  this  country,  and  Cassel  yellow  in  Ger- 
many. It  was  prepared  in  England  by  digesting  litharge 
with  half  its  weight  of  common  salt,  a  j)ortion  of  which  is 
converted  into  caustic  soda,  and  afterwards  washing  .  and 
fusing  the  oxychloride  formed.  But  it  is  sufficient  to  use 
1  part  of  salt  to  7  parts  of  oxide  of  lead  in  this  decomposition. 
Bichloride  of  lead ,  PbClj. — Bioxide  of  lead  dissolves,  with- 
out evolution  of  gas,  in  cold  dilute  hydrochloric  acid,  form- 
ing a  rose-coloured  liquid,  from  which  alkalies  throw  down  the 
bioxide  in  its  original  state.  The  rose-coloured  acid  solution, 
evaporated  in  vacuo  over  strong  potash-ley,  yields  crystals 

«  Khodius,  Ann.  Cb.  Pharra.  Ixii.  373. 


CARBONATE    OF    LEAD.  119 

of  chloride  of  lead  PbCl,  togtlier  with  crystals  of  a  different 
character,  which  appear  to  consist  of  PbClg  (Rivot,  Beudant, 
and  Daguin). 

Bromide  of  lead,  PbBr,  is  much  less  soluble  in  water  than 
the  chloride;  hence,  in  a  liquid  containing  hydrochloric  and 
hydrobromic  acids,  if  the  bromine  be  precipitated  by  acetate 
of  lead,  the  filtered  liquid  will  still  contain  chlorine,  which 
may  then  be  detected  by  adding  nitrate  of  silver  (H.  Rose). 

Iodide  of  lead,  Pbl,  229*92  or  2874. — Appears  as  a  beautiful 
lemon-yellow  powder,  when  iodide  of  potassium  is  added  to  a 
salt  of  lead.  It  is  soluble  in  194  parts  of  boiling  water,  and 
in  1235  parts  of  water  at  the  usual  temperature,  and  may  b^ 
obtained  from  solution  in  brilliant  hexagonal  scales  of  a  golden- 
yellow  colour.  A  compound  of  a  paler  yellow,  which  appears 
in  dilute  solutions  and  when  the  salt  of  lead  is  in  excess,  is  a 
basic  iodide.  M.  Denot  finds  three  oxy-iodides  of  lead,  con- 
taining 1  eq.  of  iodide  of  lead  to  1  eq.,  2  eq.,  and  5  eq.  of  oxide 
of  lead,  and  always  1  eq.  of  water,  which  last  they  do  not  lose 
below  a  temperature  of  about  400°. 

Neutral  iodide  of  lead,  Pbl,  is  decomposed  by  metallic 
chlorides,  yielding,  when  the  iodide  is  in  excess,  compounds 
which  may  be  regarded  as  iodide  of  lead,  in  which  part  of  the 
iodine  is  replaced  by  chlorine.  Sesquichloride  of  iron  and 
protochloride  of  copper  separate  free  iodine  (A.  Engelhardt). 

Cyanide  of  lead,  PbCy,  is  a  white  insoluble  powder,  obtained 
by  precipitation. 

Carbonate  of  lead,  ceruse,  white  lead;  PbO.C02;  133*56  or 
1669*5.  —  Occurs  in  nature  well  crystallised,  in  the  form  of 
carbonate  of  baryta.  It  is  precipitated  as  a  white  powder,  of 
which  the  grains,  although  very  minute,  are  crystalline,  when 
an  alkaline  carbonate  is  added  to  the  acetate  or  nitrate  of 
lead.  The  precipitate  is  anhydrous.  When  oxide  of  lead 
is  left  covered  with  water  in  an  open  vessel,  it  absorbs  car- 
bonic acid,  and  becomes  white,  forming  the  subcarbonate 
PbO.COa+PbO.HO. 

I  4 


120  LEAD. 

Carbonate  of  lead  is  invaluable  as  a  white  pij^mcnt,  from 
its  great  opacity,  which  gives  it  that  property  called  body  by 
painters,  and  enables  it  to  cover  well.  As  precipitated  by 
an  alkaline  carbonate,  it  is  deficient  in  body,  owing  to  the 
transparency  of  the  crystalline  grains  composing  the  precipi- 
tate. It  is  also  a  neutral  carbonate,  as  thus  prepared,  and 
differs  in  composition  from  the  ceruse  of  commerce,  which 
Mulder  finds  always  to  contain  hydrated  oxide  of  lead  in 
combination  with  the  carbonate  of  lead.  The  result  of 
Mulder's  analyses  of  numerous  specimens  of  white  lead,  is, 
that  there  are  three  varieties  of  that  substance,  the  composi- 
tion of  which  is  expressed  by  the  three  following  formuUe :  — 

2(PbO.C02)  +  PbO.HO; 

5iPbO.C02)+3(PbO.HO);  and 

3(PbO.C02)-}-PbO.HO. 

Mr.  J.  A.  Phillips  has  also  examined  several  specimens  of 
white  lead  prepared  by  tlie  Dutch  process.  Four  samples 
gave  by  analysis  the  formula,  2iPbO.C02)  +  PbO.HO; 
one  gave  3(PbO.C02)  +  PbO.IIO;  another,  SlPbO.COj) + 
PbO.HO.*  Dr.  T.  Richardson  also  found  that  varieties  of 
white  lead  contain  a  portion  of  oxide  of  lead,  in  addition  to 
the  carbonate,  and  so  far  confirms  the  conclusions  of  Mulder. 

In  the  old  or  Dutch  mode  of  preparing  white  lead,  which  is 
still  extensively  practised,  thin  sheets  of  the  metal  arc  placed 
over  gallipots  containing  weak  acetic  acid  (water  with  about 
2i  per  cent,  dry  acid),  themselves  imbedded  in  fermenting 
tan,  the  temperature  of  which  varies  from  1 10°  to  150°.  The 
action  is  often  very  rapid,  and  the  metal  disappears  in  a  few 
weeks  to  the  centre  of  the  sheet.  In  this  process,  from  2  to 
2\  tons  of  lead  (4480  to  5600  pounds)  are  converted  into 
carbonate,  by  a  quantity  of  vinegar  which  does  not  contain 
more  than  the  small  quantity  of  50  pounds  of  dry  acetic  acid. 
Hence  the  metal  is  certainly  neither  oxidised  nor  carbonated 
in  this  process,  at  the  expense  of  the  acetic  acid.     The  oxygen 

*  Chem.  Soc.  Qu  Vi.  iv.  p.  165. 


SALTS    OF    LEAD.  121 

must  be  derived  from  the  air,  and  the  carbonic  acid  from  the 
fermenting  tan.  In  the  newer  process,  litharge,  without  any 
preparation,  is  mixed  with  water  and  about  1  per  cent,  of 
acetate  of  lead,  and  carbonic  acid  gas  passed  over  it ;  the  oxide 
of  lead  is  rapidly  converted  into  excellent  ceruse.  There  can 
be  little  doubt  that  all  the  oxide  of  lead  is  successively  dis- 
solved by  the  acetate,  and  presented  to  the  carbonic  acid  as 
a  soluble  subacetate ;  a  compound  which,  it  is  known,  absorbs 
carbonic  acid  with  the  greatest  avidity,  and  allows  its  excess  of 
oxide  to  precipitate  as  carbonate  of  lead.  The  new  process 
supplies  likewise  the  theory  of  the  old  one,  the  function  of  the 
acetic  acid  being  manifestly  the  same  in  both  processes. 
Nitrate  of  lead  has  been  substituted  for  the  acetate,  with 
other  things  the  same  as  in  the  last  process. 

Sulphate  of  lead ;  PbO,  SO3;  151-56  or  1894-5.  — This 
salt  is  precipitated  when  sulphuric  acid  or  a  soluble  sulphate 
is  added  to  a  solution  of  acetate  or  nitrate  of  lead,  as  a  white, 
dense,  insoluble  precipitate,  which  appears  by  the  microscope 
to  be  composed  of  minute  crystals.  It  is  also  formed  by  the 
action  of  strong  nitric  acid  on  sulphide  of  lead.  Sulphate  of 
lead  contains  in  100  parts,  26'44  sulphuric  acid  and  73-56 
oxide  of  lead,  and  may  be  exposed  to  a  red  heat  without  de- 
composition. Dr.  Richardson  finds  that  this  salt  acquires 
considerable  opacity,  and  may  be  substituted  for  ceruse,  when 
prepared  in  a  mode  analogous  to  the  new  process  for  that 
substance ;  namely,  by  supplying  sulphuric  acid,  in  a  gradual 
manner,  to  a  thick  mixture  of  litharge  and  water  containing 
a  small  proportion  of  acetate  of  lead.  In  this  manner  the 
sulphate  of  lead  may  be  obtained  united  with  any  desirable 
excess  of  oxide  of  lead. 

Nitrate  of  lead ;  PbO.NOs;  165-56  or  2069-5.  —  Obtained 
by  dissolving  litharge,  at  the  boiling  point,  in  slightly  diluted 
nitric  acid,  which  should  be  free  from  hydrochloric  and  sul- 
phuric acids.  The  neutral  nitrate  crystallises  in  large  octo- 
hedrons,  with   the  secondary  faces  of  the  cube,  sometimes 


122  LEAD. 

transparent,  although  generally  white  and  opaque.  The  crystals 
are  anhydrous ;  they  are  soluble  in  7^  times  their  weight  oi 
cold,  and  in  a  much  smaller  quantity  of  hot  water.  Nitrate 
of  lead  is  decomposed  by  an  incipient  red  heat,  yielding  a 
mixture  of  oxygen  gas  and  peroxide  of  nitrogen  (which  is  pre- 
pared in  this  way),  and  leaving  the  yellow  oxide  of  lead. 
When  a  small  quantity  of  ammonia  is  added  to  nitrate  of  lead, 
or  w^hen  a  dilute  solution  of  the  neutral  salt  is  boiled  with 
oxide  of  lead  in  fine  powder,  a  soluble  bibasic  nitrate  of  lead 
is  formed  PbO.NOg  +  PbO.  It  crystallises  during  evaporation 
in  fine  scales,  or  in  little  opaque  grains,  which  are  anhydrous. 
The  granular  crystals  decrepitate  when  heated,  with  extraor- 
dinary force.  The  tribasic  nitrate  of  lead  precipitates  when 
ammonia  is  added  in  very  slight  excess  to  a  solution  of 
nitrate  of  lead.  Its  constituents  are  2(3PbO.N05)4-3HO 
(Berzelius).  It  is  a  white  powder,  which  is  soluble  to  a  small 
extent  in  pure  water.  When  nitrate  of  lead  is  digested  with 
a  considerable  excess  of  ammonia,  the  decomposition  stops  at 
the  point  at  which  6  eq.  of  oxide  of  lead  arc  combined  with 
1  eq.  of  nitric  acid.  The  sexbasic  nitrate  of  lead  contains 
2(6PbO.N05)+ 3H0  (Berzelius). 

Nitrites  of  lead.  —  When  a  solution  of  100  parts  of  nitrate 
of  lead  is  boiled  with  78  parts  of  metallic  lead  in  thin  turn- 
ings, the  lead  is  dissolved,  and  a  little  nitric  oxide  is  evolved, 
in  consequence  of  a  partial  decomposition  of  nitrous  acid 
previously  formed.  The  solution  is  alkaline  and  yellow ;  and 
gives,  on  cooling,  brilliant  crystalline  plates  of  a  golden  yellow 
colour,  which  consist  of  the  bibasic  nitrite  of  leady  2PbO.N03. 
By  dissolving  100  parts  of  this  salt  in  water  at  107°  (75°  C), 
and  then  mixing  with  the  solution  35  parts  of  oil  of  vitriol, 
previously  diluted  with  four  times  its  weight  of  water,  one 
half  of  the  oxide  of  lead  is  precipitated  as  sulphate  of  lead,  and 
a  solution  is  obtained  of  a  deep  yellow  colour,  from  which  the 
neutral  nitrite  of  lead,  PbO.NOg  +  HO,  crystallises.  This  salt 
gives  yellow  crystals,  resembling  the  nitrate  in  form.     Its 


SALTS    or    LEAD.  l;^3 

solution  absorbs  oxygen  from  the  air,  and,  like  all  the  nitrites, 
gives  off  nitric  oxide  at  176°  (80°  C),  while  a  subnitrite  of  lead 
precipitates.  Berzelius,  to  whom  we  are  indebted  for  the 
preceding  facts,  also  formed  a  quadribasic  nitrite  of  lead,  con- 
taining N03.4PbO  +  HO,  by  boiling  1  part  of  nitrate  of  lead, 
and  1  \  parts  or  more  of  metallic  lead,  in  a  long-necked  flask 
for  12  hours,  then  filtering  and  leaving  the  solution  to  crys- 
tallise by  cooling :  it  thus  yields  pale,  flesh-coloured,  silky 
needles,  or,  if  rapidly  cooled,  a  white  powder. 

The  nitrites  of  lead  have  also  been  examined  by  other 
chemists,  who  have  obtained  results  differing  from  those  of 
Berzelius.  Thus,  Peligot  and  others  found  that  Berzelius^s 
bibasic  nitrite  contains  the  elements  of  2  eq.  of  oxide  of  lead, 
1  eq.  of  hyponitric  acid,  NO4,  and  1  eq.  of  water.  Gerhardt 
therefore  regards  it  as  a  compound  of  bibasic  nitrate  and 
bibasic  nitrite  of  lead  : — 

2(PbO.N04)  =  2PbO.N03  +  2PbO.N05. 

and  expresses  its  formation  by  the  equation : — 

2(PbO.N©5)  +  2Pb  =  2PbO.N05  +  2PbO.N03. 

If  the  action  of  the  metallic  lead  be  further  continued,  a  fresh 
portion  of  nitrate  is  deoxidised,  and  the  result  is  an  orange- 
coloured  salt,  containing  7Pb0.2N04  (Peligot),which  Gerhardt 
regards  as  a  double  salt  more  basic  than  the  former : 
7Pb0.2N04  =  4PbO.N03  +  SPbO.NO^. 

Finally,  by  the  continued  action  of  the  lead,  the  subnitrate 
contained  in  these  two  salts  is  likewise  reduced,  and  a  sub- 
nitrite  is  formed,  viz.,  either  Berzelius^s  quadrobasic  salt, 
4PbO.N03,  or  a  bibasic  nitrite  2PbO.N03,  obtained  by 
Bromeis.  The  last  salt  crystallises  in  long  golden-yeUow 
needles  containing  1  eq.  of  water.* 

Phosphate  of  lead. — On  mixing  nitrate  of  lead  with  ordi- 

*  For  a  more  detailed  account  of  the  nitrates  and  nitrites  of  lead,  see 
Gmelin's  Handbook,  Translation,  v.  152—157. 


12 i  LEAD. 

nary  phosphate  of  soda,  a  precipitate  is  formed  coutaiiiing  the 
two  salts  SPbO.PO^  and  2PbO.IIO.PO5.  The  latter  is  obtained 
pure  by  precipitating  a  boiling  solution  of  nitrate  of  lead  with 
pure  phosphoric  acid.  This  salt  dissolves  in  nitric  acid  and 
fixed  alkalies,  but  very  sparingly  in  acetic  acid;  ammonia 
converts  it  into  SPbO.POg.  It  fuses  readily  before  the  blow- 
pipe, and  crystallises  on  coolmg  in  well  defined  polyhedrons. 
When  strongly  ignited  with  charcoal,  it  gives  off  phosphorus 
and  carbonic  oxide,  and  leaves  metallic  lead. 

Chlorite  of  lead,  PbO.ClO^,  is  obtained  in  sulphur-yellow 
crystalline  scales  by  precipitating  nitrate  of  lead  T\dth  an  excess 
of  chlorite  of  barj^ta  containing  free  chlorous  acid.  It  decora- 
poses  at  259°  with  a  kind  of  explosion,  and  sets  fire  to 
flowers  of  sulphur  triturated  with  it.  Sulphuric  acid  diluted 
with  an  equal  weight  of  water,  decomposes  it,  especially  between 
104°  and  122°,  evolving  pure  chlorous  acid  gas,  and  leaving 
88'75  per  cent,  of  sulphate  of  lead  (Millon). 

Chlorate  of  lead,  PbO.ClOg  +  HO,  is  obtained  by  cooling  a 
hot  solution  of  oxide  of  lead  in  aqueous  chloric  acid,  in  rhom- 
boidal  prisms  belonging  to  the  oblique  prismatic  system,  and 
isomorphous  with  the  analogously  constituted  crystals  of 
chlorate  of  baryta.  These  crystals,  when  heated,  leave  the 
yellow  oxychloride  Pb0.2PbCl  (Vauquelin,  Wiichter,  Yogel). 

Perchlorate  of  lead,  Pl)O.C107. — The  solution  of  oxide  of 
lead  in  warm  aqueous  perchloric  acid,  yields  small  prisms 
having  a  sweet  but  highly  astringent  taste,  soluble  in  their 
own  weight  of  water,  but  not  deliquescent  (Serullas).  By  boiling 
a  concentrated  solution  of  this  salt  with  carbonate  of  lead,  a 
solution  of  a  basic  salt  is  obtained,  which  if  the  excess  of 
base  is  very  large,  yields  by  evaporation,  dull,  indistinct 
crystals,  which  are  resolved  by  water  into  a  solution  of  bibasic 
salt,  and  a  white  insoluble  residue.  AVlien  the  excess  of  base 
is  less,  or  when  the  solution  of  the  bibasic  salt  is  left  to  evapo- 
rate, ci^stals  of  two  different  forms  are  obtained ;  both,  how- 
ever, containing  2PbO.C107  +  21IO  (Marignac). 


SALTS    OF    LEAD.  123 

Chlorophosphate  of  had^  PbCl  +  3(3PbO.P05),  occurs  as 
pyromorphite  and  green  and  brown  lead- ore.  The  crystals 
belong  to  the  hexagonal  system,  and  have  the  hardness  of 
apatite.  It  fuses  readily,  and  on  cooling  solidifies  with  vivid 
incandescence  into  an  angular  crystalline  mass.  In  some  of 
these  ores,  the  chloride  of  lead  is  partly  replaced  by  fiuoride 
of  calcium,  and  the  triphosphate  of  lead  by  the  triphosphate 
of  calcium  or  trisarscniate  of  lead.  The  calcareous  ores  may 
be  regarded  as  mixtures  of  apatite  and  pyromorphite.  The 
same  compound  containing,  however,  an  atom  of  water,  is 
formed  artificially  on  pouring  a  boiling  solution  of  chloride  of 
lead  into  a  boiling  solution  of  phosphate  of  soda,  the  latter 
being  in  excess  (Ileintz).  When,  on  the  contrary,  a  boiling 
solution  of  phosphate  of  soda  is  poured  into  an  excess  of 
chloride  of  lead,  a  precipitate  is  formed,  which,  according  to 
Heintz,  is  2(3PbO.P05)  +  PbCl,  but,  according  to  Gerhardt, 
2PbO.HO.P05  +  PbCl. 

Acetate  of  lead,  PbO.(C4H303)  h3H0.— This  salt  is  met 
with  well  crystallised,  and  in  a  state  of  great  purity,  in  com- 
merce. It  is  generally  prepared  by  dissolving  litharge  in  the 
acetic  acid  procured  by  the  distillation  of  wood.  It  crystal- 
lises in  flattened  four-sided  prisms ;  has  a  taste  which  is  first 
sweet  and  then  astringent ;  is  very  soluble  in  water,  100  parts 
of  water  dissolving  59  of  the  salt  at  60°;  and  dissolves  in  8  parts 
of  alcohol.  It  effloresces  in  air,  and  is  apt  to  be  partially 
decomposed  by  the  carbonic  acid  of  the  air,  and  thus  to  become 
partially  insoluble.  It  loses  the  whole  of  its  water  when  dried 
at  the  usual  temperature  in  vacuo.  M.  Payen  crystallised  the 
anhydrous  acetate  from  solution  in  absolute  alcohol. 

Tribasic  subacetate  of  lead,  PbO.(C4ll303)  -f  2PbO,is  formed 
by  digesting  oxide  of  lead  in  a  solution  of  the  neutral  salt,  till 
it  is  strongly  alkaline.  This  salt  does  not  crystallise  when  so 
prepared,  but  may  be  dried,  and  then  contains  no  water.  It 
is  very  soluble,  but  must  be  dissolved  in  distilled  water,  as  the 
carbonic,  hydrochloric  and  other  acids  in  well  wa.er  precipi- 


126  LEAD. 

tate  its  oxide  of  lead.  M.  Payen  lias  observed  that  the  tribasic 
subacetate  crystallises  readily,  in  fine  prismatic  needles,  when 
formed  by  adding  ammonia  to  a  moderately  strong  solu- 
tion of  the  neutral  acetate.  The  crystals  contain  1  eq.  of 
water,  which  they  lose  at  212°.  The  acetate  of  ammonia, 
formed  at  the  same  time,  appears  to  give  stability  to  the  sub- 
acetate  of  lead  in  solution,  and  prevents  an  excess  of  a  whole 
equivalent  of  ammonia  from  throwing  down  any  oxide  of  lead 
from  the  solution.  This  ammoniacal  solution  of  the  subacetate 
of  lead,  prepared  without  an  excess  of  ammonia,  is  a  con- 
venient form  in  which  to  apply  that  salt  as  a  reagent.* 

Sesquibasic  acetate  of  lead,  3Pb0.2(C^Il303)-f  HO.— This 
salt  was  obtained  by  Payen  by  adding  1  cq.  of  the  neutral 
acetate  to  a  concentrated  and  boiling  solution  of  1  eq.  of  the 
tribasic  acetate.  It  is  also  produced  when  the  neutral  and 
anhydrous  acetate  of  lead  is  heated  in  a  retort  or  porcelain 
capsule,  till  the  whole,  after  being  liquid,  becomes  a  white  and 
porous  mass.  The  sesquibasic  acetate  is  then  formed  by  the 
decomposition  of  3  eq.  of  neutral  acetate  of  lead,  from  which 
there  separate  the  elements  of  1  eq.  of  acetic  acid,  in  the 
form  of  carbonic  acid  and  acetone  (Matteucci  and  Wohler). 
This  basic  salt  is  very  soluble,  and  crystallises  in  plates  of  a 
pearly  lustre.  Another  method  of  obtaining  it  is  to  digest  an 
aqueous  solution  of  2  eq.  of  the  neutral  acetate  with  1  eq.  of 
protoxide  of  lead  free  from  carbonate,  till  it  dissolves,  and 
evaporate  the  filtrate  in  vacuo  over  oil  of  vitriol. 

A  sexbasic  acetate  of  lead,  6PbO.(C4H303),  is  formed  on 
dropping  a  solution  of  the  neutral,  or  of  triliasic  acetate  of 
lead,  into  excess  of  ammonia.  It  is  a  white  precipitate,  which 
when  examined  by  the  microscope,  has  a  crystalline  aspect. 
It  contains  a  little  water,  which  it  loses  when  dried  in  vacuo. 

A  bibasic  acetate,  2PbO.(C4H303),  is  also  formed,  accord- 


•  Memoire  sur  lee  Acetates  et  le  Protoxide  de  Plomb,  par  M.  Pajen,  An. 
de  Chim,  et  de  Phys.  t.  Ixvi.  p.  37. 


ALLOYS    OF    LEAD.  127 

ing  to  Dobereiner  and  Scliindler,  by  boiling  1  eq.  of  neutral 
acetate  of  lead  with  1  eq.  of  the  protoxide. 

The  common  extrokctum  Saturni  of  the  pharmacopoeias  ap- 
pears to  consist  chiefly  of  bibasic  acetate_,  containing  more  or 
less  of  the  tribasic  and  sesquibasic  salts. 

Alloys  of  lead. — Lead  and  tin  may  be  fused  together  in  all 
proportions.  M.  E-udberg  finds  that  these  metals  combine  in 
certain  definite  proportions^  having  fixed  points  of  congela- 
tion :  — 

1  atom  of  lead  and  3  atoms  of  tin^  congeal  at  368*6°. 

1  atom  of  lead  and  1  atom  of  tin,  at  464°. 

2  atoms  of  lead  and  1  atom  of  tin,  at  518°. 

3  atoms  of  lead  and  1  atom  of  tin,  at  536°. 

A  thermometer  placed  in  a  fluid  alloy  of  1  atom  of  lead  and 
2  atoms  of  tin,  becomes  stationary  when  the  temperature  falls 
to  392° ;  a  portion  then  solidifies,  and  a  more  fusible  alloy 
separates;  the  temperature  again  falls,  and  afterwards  be- 
comes stationary  at  368*6°,  the  crystallising  point  of  the  alloy 
composed  of  1  atom  of  lead  and  3  atoms  of  tin.  If  the  alloy 
contains  so  much  tin  that  its  point  of  complete  congelation  is 
below  368*6°,  the  last  compound  always  separates  from  it  at 
that  point,  and  the  thermometer  remains  stationary  for  a 
time,  whatever  may  be  the  proportion  of  the  metals  in  the 
alloy.*  Fine  solder  is  an  alloy  of  2  parts  of  tin  and  1  of  lead ; 
it  fuses  at  about  360°,  and  is  much  employed  in  tinning 
copper.  Coarse  solder  contains  one  fourth  of  tin,  and  fuses 
at  about  500° ;  it  is  the  substance  employed  for  soldering  by 
plumbers. 

Lead,  as  reduced  from  the  native  sulphide,  always  contains 
a  little  silver.  The  latter  is  separated  by  allowing  two  or  three 
tons  of  the  melted  metal  to  cool  slowly  in  a  hemispherical  iron 
pot,  when  the  lead,  as  it  solidifies,  separates  in  crystals,  which 
can  be  raked  out.     The  silver  remains  almost  wholly  in  the 

*  Eudborg,  An.  Ch.  Phys.  [2.]  xlviii.  363. 


128  LEAD. 

more  fusible  portion,  or  wliat  may  be  looked  upon  as  tlie 
mother- liquor  of  these  crystals;  so  that  by  this  operation 
the  argentiferous  alloy  is  greatly  concentrated.  This  mode  of 
separation  was  discovered  by  Mr.  Pattinson  of  Newcastle. 
To  separate  the  remaining  lead,  much  of  it  is  converted  into 
massicot,  by  the  action  of  air  upon  its  surface,  in  the  shallow 
furnace  used  for  that  preparation ;  and  the  last  portions  of 
lead  are  removed  by  continuing  the  oxidation  upon  a  porous 
bason  or  cupel  of  bone-earth,  whicli  imbibes  the  fused  oxide  of 
lead,  while  the  melted  silver  is  found  in  a  state  of  purity  upon 
the  surface  of  the  cupel,  not  being  oxidable  at  a  high  tem- 
perature. 


ESTIMATION    OF    LEAD,    AND    METHODS    OF    SEPARATING    IT    FROM 
THE    PRECEDING    METALS. 

Lead  may  be  estimated  either  as  protoxide  or  as  sul- 
phate. For  the  former  mode  of  estimation,  it  is  best  to  pre- 
cipitate by  oxalate  of  ammonia,  the  solution  being  neutral 
or  rendered  very  slightly  alkaline  by  ammonia.  The  oxalate 
of  lead,  after  being  washed  and  dried,  is  then  to  be  ignited 
in  an  open  porcelain  crucible,  whereby  it  is  converted  into 
protoxide.  As  lead  is  very  easily  reduced  by  carbonaceous 
matter  at  a  red  heat,  the  precipitate  must  not  be  ignited 
in  contact  with  the  filter ;  but  the  filter,  after  the  greater 
part  of  the  precipitate  has  been  removed  from  it,  must  be 
held  on  the  point  of  a  fine  platinum  wire  above  the  cru- 
cible, and  set*  on  fire,  so  that  the  ashes  may  drop  in  ;  the 
precipitate  may  then  be  added,  and  the  ignition  completed. 
The  protoxide  contains  92-83  per  cent,  of  metallic  lead.  Lead 
may  also  be  precipitated  by  carbonate  of  ammonia,  to  which 
a  little  free  ammonia  has  been  added,  and  the  carbonate  of 
lead  treated  as  above. 

In  precipitating  lead  as  sulphate,  if  the  solution  be  neutral, 
the  precipitation  is  best  eftectcd  by  sulphate  of  soda ;  the  sul- 


ALLOYS   OF    LEAD.  129 

phate  of  lead  may  then  be  washed  on  a  filter,  dried  and 
ignited ;  but  if  the  solution  contains  free  nitric  acid,  it  is  best 
to  precipitate  by  excess  of  sulphuric  acid,  then  evaporate  to 
dryness,  and  ignite  till  all  excess  of  acid  is  driven  off;  treat 
the  residue  with  water  to  dissolve  out  any  soluble  salts  that 
may  be  present ;  wash  the  sulphate  of  lead  on  a  filter,  and 
then  dry  and  ignite  it,  burning  the  filter  separately  as  above. 
The  sulphate  contains  68*32  per  cent,  of  lead. 

From  the  alkalies  and  earths,  and  from  manganese,  iron, 
cobalt,  nickel,  and  zinc,  lead  is  easily  separated  by  hydrosulphuric 
acid,  the  solution  being  previously  acidulated  with  nitric  acid. 
The  precipitated  sulphide  is  washed  and  dried,  then  placed, 
together  with  the  filter  (which  should  be  as  small  as  possible), 
in  a  porcelain  dish,  covered  over  with  a  glass  plate  or  a  funnel, 
and  treated  with  fuming  nitric  acid,  added  cautiously  and  by 
small  portions  at  a  time.  Violent  action  takes  place,  and  the 
sulphide  of  lead  is  converted  into  sulphate.  A  portion  may, 
however,  be  converted  into  nitrate,  with  separation  of  sul- 
phur: hence,  to  insure  complete  conversion  into  sulphate, 
it  is  necessary  to  add  a  few  drops  of  strong  sulphuric  acid. 
The  product  must  then  be  strongly  ignited  to  drive  off  the 
excess  of  sulphuric  acid,  and  burn  away  the  remaining  organic 
matter  of  the  filter. 

From  cadmium  and  copper,  lead  is  easily  separated  by  sul- 
phuric acid. 


VOL.  II. 


130  TIN. 


ORDER  V. 

OTHER  METALS  PROPER  HAVING  ISOMORPHOUS  RELATIONS 
WITH   THE  MAGNESIAN  FAMILY. 


SECTION    I. 

TIN. 

Eq.  58-82  or  735*25;  Sn  (siannum). 

Tin  does  not  occur  native,  but  its  common  ore  is  reduced 
by  a  simple  process,  and  mankind  appear  to  have  been  in 
possession  of  this  metal  from  the  earliest  ages.  The  most 
productive  mines  of  tin  are  those  of  Cornwall,  from  which 
the  ancients  appear  to  have  derived  their  principal  supply 
of  this  metal,  and  those  of  the  peninsula  of  Malacca  and 
island  of  Banca  in  India. 

The  only  important  ore  of  tin  is  the  bioxide,  which  is  found 
in  Cornwall,  both  in  veins  traversing  the  primary  rocks,  and 
in  alluvial  deposits  in  their  neighbourhood.  In  the  latter 
case,  the  ore  presents  itself  in  rounded  grains  of  greater  or 
less  size,  which  form  together  a  bed  covered  by  clay  and 
gravel.  This  ore  has  evidently  been  removed  from  its  original 
situation,  and  the  grains  rounded  by  the  action  of  water, 
which  has  at  the  same  time  divested  it  of  the  other  metallic 
ores  with  which  it  is  accompanied  in  the  vein;  these  being 
softer  are  more  easily  reduced  to  powder,  and  have  been 
carried  away  by  the  stream.  This  ore,  called  stream  tin,  is 
easily  reduced  by  coal,  and  gives  the  purest  tin.  The  metal 
from  the  ore  of  the  veins  is  contaminated  with  iron,  copper, 
arsenic,  and  antimony,  from  which  a  portion  of  it  is  par- 
tially purified  by  liquation.      Bars  of  the  impure  metal  arc 


PROTOXIDE    OF    TIN.  131 

exposed  to  a  moderate  heat,  by  wliicli  the  pure  tin  is  first 
melted,  and  separates  it  from  a  less  fusible  alloy  containing 
the  foreign  metals.  The  pm^er  portion  is  called  grain  tin, 
and  the  other,  ordinary  tin  or  block  tin.  The  mass  of  grain 
tin  is  heated  till  it  becomes  brittle,  and  then  let  fall  from 
a  height.  By  this  it  splits  into  irregular  prisms,  somewhat 
resembling  basaltic  columns.  This  splitting  is  a  mark  of  the 
purity  of  the  tin,  for  it  does  not  happen  when  the  tin  is 
contaminated  by  other  metals. 

Pure  tin  is  white,  with  a  bluish  tinge,  very  soft,  and  so 
malleable,  that  it  may  be  beaten  into  thin  leaves,  tinfoil  not 
being  more  than  1- 1000th  of  an  inch  in  thickness.  When 
a  bar  of  tin  is  bent,  it  emits  a  grating  sound,  which  is  cha- 
racteristic;  and  when  bent  backwards  and  forwards  rapidly, 
several  times  in  succession,  becomes  so  hot  that  it  cannot 
be  held  in  the  hand.  At  the  temperature  of  boiling  water, 
tin  can  be  drawn  out  into  wire,  which  is  very  soft  and 
flexible,  but  deficient  in  tenacity.  The  density  of  pure  tin  is 
7*285,  or  7*293  after  being  laminated;  that  of  the  tin  of  com- 
merce is  said  to  vary  from  7*56  to  7'Q.  Its  point  of  fusion  is 
442°,  according  to  Crichton  and  Rudberg;  4456°,  according 
to  KupfFer.  Tin  is  volatile  at  a  very  high  temperature.  The 
brilliancy  of  the  surface  of  tin  is  but  slowly  impaired  by 
exposure  to  air,  and  even  in  water  it  is  scarcely  acted  upon. 
Hence  the  great  value  of  this  metal  for  culinary  vessels,  and 
for  covering  the  more  oxidable  metals,  such  as  ii'on  and  copper, 
when  employed  as  such.  Three  oxides  of  tin  are  known,  the 
protoxide  SnO,  sesquioxide  Sn203,  and  bioxide  Sn02. 

Protoxide  of  tin.  Stannous  oxide;  SnO,  66*82  or  835*25. 
Tin  dissolves  in  undiluted  hydrochloric  acid,  at  the  boiling 
temperature,  by  substitution  for  hydrogen,  and  forms  the  pro- 
tochloride  of  tin.  From  this  the  protoxide  is  precipitated  by 
an  alkaline  carbonate,  as  a  white  hydrate,  which  may  be 
washed  with  tepid  water  and  dried  at  a  temperature  not  ex- 
ceeding 176°.     It  does  not  contain  a  trace  of  carbonic  acid. 

z  2 


132  TIN. 

This  white  powder  dried  more  strongly  in  a  retort  filled  with 
carbonic  acid,  and  heated  to  redness,  gives  the  anhydrous 
oxide  as  a  black  powder,  the  density  of  which  is  6*666.  In 
this  state,  the  oxide  is  permanent;  but  if  a  body  at  a  red 
heat  is  brought  in  contact  with  it  in  open  air,  it  takes  fire  and 
burns,  and  is  entirely  converted  into  bioxide.  If  hydrated  stan- 
nous oxide  be  boiled  with  a  quantity  of  potash  not  sufficient 
to  dissolve  it  entirely,  the  undissolved  portion  is  converted 
into  small,  hard,  shining,  black  crystals  of  anhydrous  stan- 
nous oxide,  which,  when  heated  to  392°,  decrepitate,  swell 
up,  fall  to  pieces,  and  are  converted  into  an  olive-green 
powder,  consisting  also  of  the  anhydrous  protoxide.  Again, 
on  evaporating  a  very  dilute  solution  of  sal-ammoniac,  in 
which  hydrated  stannous  oxide  is  diff'used,  that  compound 
is  converted,  as  soon  as  the  sal-ammoniac  crystalli.es,  into 
anhydrous  stannous  oxide,  having  the  form  of  a  cinnabar- 
coloiu-ed  po-\vder.  There  are,  therefore,  three  modifications 
of  stannous  oxide,  black,  olive-green,  and  red  (Fremy).  The 
red  modification  is  also  obtained  by  digesting  thoroughly 
washed  hydrated  stannous  oxide  at  a  temperature  of  133°,  in 
a  slightly  acid  solution  of  stannous  acetate,  having  a  density 
of  1-06  (Roth). 

Protoxide  of  tin  dissolves  in  acids,  and  with  more  faci- 
lity when  hydrated  than  after  being  ignited.  This  oxide  is 
also  dissolved  by  potash  and  soda,  but  the  solution  after 
a  time  undergoes  decomposition ;  metallic  tin  is  deposited, 
and  the  bioxide  is  found  in  solution.  The  solution  of  a 
stannous  salt,  and  of  a  stannic  salt  also,  is  apt  to  undergo 
decomposition,  when  largely  diluted  with  water,  and  to 
deposit  a  subsalt.  Stannous  salts  absorb  oxygen  from  the 
air,  and  have  a  great  affinity  for  that  element ;  they  convert 
the  sesquioxide  of  iron  into  protoxide,  and  throw  down  mer- 
cury, silver  and  platinum  in  the  metallic  state  from  their 
solutions.  Chloride  of  gold  produces  a  purple  precipitate  in  a 
stannous  salt,    consisting,   it  is   believed,  of  the   l)ioxide  of 


STANNOUS  COMPOUNDS.  138 

tin  in  combination  with  protoxide  of  gold,  a  test  by  which  the 
protoxide  of  tin  may  always  be  distinguished.  Hydrosulphuric 
acid  produces  in  neutral  or  acid  solutions  of  stannous  salts, 
a  brown-black  precipitate  of  protosulphide  of  tin,  which,  when 
gently  heated  with  a  considerable  quantity  of  sulphide  of  am- 
monium containing  excess  of  sulphur,  is  converted  into  the 
bisulphide  and  dissolved;  acids  added  in  excess  to  this  solu- 
tion precipitate  the  yellow  bisulphide.  Caustic  alkalies  and 
alkaline  carbonates,  added  to  stannous  salts,  throw  down  a 
white  precipitate  of  hydrated  stannous  oxide,  soluble  in  caustic 
potash  or  soda,  but  not  in  ammonia.  Ferrocyanide  of  potas- 
sium produces  a  white  precipitate,  soluble  in  hydrochloric 
acid. 

Protosulphide  of  tin,  SnS,  is  formed  when  sulphur  is  mixed 
with  tin  heated  above  its  melting  point ;  it  is  also  obtained 
in  small  dark  grey  crystalline  laminse,  of  sp.  gr.  4*973,  by 
adding  the  hydrated  sulphide  precipitated  from  a  stannous 
salt  by  hydrosulphuric  acid,  to  anhydrous  protochloride  of  tin 
in  the  melted  state,  and  removing  the  excess  of  the  proto- 
chloride with  dilute  hydrochloric  acid.  It  is  decomposed  by 
dilute  hydrochloric  acid,  with  evolution  of  hydrosulphuric  acid. 

Protochloride  of  tin,  Salt  of  tin ;  SnCl. — This  salt  may  be 
obtained  in  the  anhydrous  state  by  gradually  heating  a 
mixture  of  equal  weights  of  calomel  and  tin,  and  finally  dis- 
tilling the  protochloride  at  a  strong  red  heat.  The  fused 
mass  on  cooling  forms  a  grey  solid,  of  considerable  lustre,  and 
having  a  vitreous  fracture.  The  hydrated  chloride,  known 
in  commerce  as  salt  of  tin,  is  procured  by  evaporating  the 
solution  of  tin  in  concentrated  hydrochloric  acid  to  the 
point  of  crystallisation.  It  is  thus  obtained  in  needles,  or 
in  larger  four-sided  prismatic  crystals  containing  2  eq.  of 
water.  They  fuse  between  100°  and  105°.  The  specific 
gravity  of  the  crystals  is  2*710  at  60° ;  that  of  the  fused  mass 
at  100°,  is  2-588  (Penny).  The  salt  parts  with  the  greater 
portion,  if  not  the  whole  of  its  water  at  212°,  but  if  distilled 

K  3 


13i  TIN. 

at  a  higher  temperature,  loses  hydrochloric  acid  also,  and 
leaves  an  oxychloride  of  tin.  It  dissolves  completely  in  a 
small  quantity  of  water ;  but  when  treated  with  a  large  quan- 
tity, is  partly  decomposed,  hydrochloric  acid  being  dissolved, 
and  a  light  milk-Avhite  powder  separating,  which  is  a  basic 
chloride,  or  oxy chloride,  SnCl.SnO  +  2 HO.  Both  the  crys- 
tals and  the  solution  absorb  oxygen  from  the  air,  and  then  a 
basic  salt  of  the  sesquioxide  is  formed  which  is  also  insoluble 
in  water.  From  both  these  causes,  a  complete  and  clear  solu- 
tion of  the  salt  of  tin  is  rarely  obtained,  imlcss  the  water  is 
previously  acidulated  with  hydrochloric  acid.  This  salt  is  en- 
tirely soluble  in  caustic  alkali,  but  the  solution  is  liable  to  an 
ulterior  change  already  mentioned.  One  part  of  crystallised 
protochloride  of  tin  dissolved,  together  with  3  parts  of  tartaric 
acid,  in  a  sufficient  quantity  of  hot  water,  and  carefully  neu- 
tralised with  potash,  forms  a  clear  sohition,  whicli  may  be 
boiled  and  mixed  with  any  quantity  of  water  without  becoming 
turbid:  the  white  precipitate  which  forms  in  it  on  the  addition 
of  a  little  more  potash,  especially  on  heating,  is  redissolved 
by  a  lai'ger  quantity  of  potash  (R.  Schneider) . 

When   protochloride  of  tin  is  heated  with  a  mixture  of 
hydrochloric  and  sulphurous  acids,  a  yellow  precipitate  of  bi- 
sulphide of  tin   is   formed:  6SnCH- 2S0.^  +  4liCl=  SnS2  4- 
SSnClj  -r  4110.     This  reaction  serves  as  a  test  for  sulphurous 
acid. 

The  protochloride  of  tin  is  used  in  calico-printing,  not  only 
as  a  mordant,  but  also  as  a  deoxidising  agent,  particularly  to 
deoxidise  indigo,  and  to  reduce  to  a  lower  state  of  oxidation 
and  discharge  the  sesquioxides  of  iron  and  manganese  fixed 
upon  cloth. 

Protochloride  of  tin  and  potassium ;  SnCl.KCl. — Proto- 
chloride of  tin  forms  a  double  salt  w  ith  chloride  of  potassium, 
and  also  with  chloride  of  ammonium,  which  compounds  crys- 
tallise in  the  anhydrous  state,  and  also  with  3  eq.  of  water, 
or,  according  to  Rammelsberg,  with  only  1  equivalent. 


STANNOUS    COMPOUNDS.  135 

Anhydrous  protochloride  of  tin  fused  in  ammoniacal  gas, 
absorbs  half  an  equivalent  of  that  gas_,  according  to  Persoz, 
forming  2SnCl.NH3,  or  rather  perhaps  SnCL(NH3Sn)Cl. 

Protiodide  of  tiny  SnI,  is  formed  by  heating  a  mixture  of 
granulated  tin  and  iodine.  It  is  obtained  in  beautiful  shining 
yellowish  red  prisms  by  gently  boiling  concentrated  hydriodic 
acid  with  strips  of  tinfoil  in  a  long  glass  tube  for  a  day,  or 
more  readily  by  heating  the  acid  with  the  tin  in  a  sealed  glass 
tube  to  a 'temperature  of  248°,  or  at  most  302°  for  an  hour ; 
after  cooling,  the  remaining  portion  of  tin  is  found  to  be 
covered  with  crystals.  When  tinfoil  and  iodide  of  amyl  were 
heated  together  in  a  sealed  tube  for  a  day  to  356°,  the  tinfoil 
became  covered  with  yellowish-red  quadratic  octohedrons  at 
the  part  where  the  tube  cooled  most  quickly ;  but  at  the  part 
which  was  immersed  in  the  oil-bath,  and  therefore  cooled  more 
slowly,  the  metal  was  covered  with  sulphur-yellow  prisms, 
which  became  yellowish-red  when  taken  out  (Wohler). 
Stannous  iodide  was  found  by  Boullay,  jun.,  to  form  double 
salts  with  other  iodides,  particularly  with  the  iodides  of  the 
alkaline  and  earthy  metals,  in  which  two  atoms  of  the  stannous 
iodide  are  combined  with  one  of  the  other  iodide. 

Carbonic  acid  does  not  combine  with  either  of  the  oxides 
of  tin. 

Protosulphate  of  tin j  SnO.SOg. — Tin  dissolves  in  sulphuric 
acid,  concentrated  or  a  little  diluted,  yielding  a  saline  mass, 
which  forms  a  brown  solution  in  water  and  deposits  small 
crystalline  needles  on  cooling. 

Protonitrate  of  tin,  SnO.NOg,  is  obtained  by  dissolving 
hydrated  protoxide  of  tin  in  nitric  acid ;  the  solution  cannot 
be  concentrated  and  is  easily  altered. 

Tartrate  of  potash  and  tin,  KO.SnO.(C8H40iQ)  or 
C8H4(KSn)Oi2- — Bitartrate  of  potash  dissolves  protoxide  of 
tin,  and  forms  a  very  soluble  salt  of  potash  and  tin,  which,  like 
most  of  the  tartrates,  is  not  precipitated  either  by  caustic 
alkalies  or  by  alkaline  carbonates.     An  addition  of  bitartrate 

K   4t 


136  TIN. 

of  potash  is  occasionally  made  to  the  solution  of  tin  used 
in  dyeing. 

Sesquioxide  of  tirij  Sn203. — Was  obtained  by  M.  Fuchs,  by 
diffusing  recently  precipitated  sesquioxide  of  iron  in  a  solution 
of  protochloride  of  tin  containing  no  excess  of  acid,  and 
afterwards  boiling  the  mixture.  A  double  decomposition 
occurs,  in  which  sesquioxide  of  tin  precipitates,  and  proto- 
chloride of  iron  is  retained  in  solution  : 

2SnCl  +  Fe203  =  Sn^Og  +  2FeCl. 

The  sesquioxide  thus  obtained  is  a  slimy  grey  matter,  and 
usually  yellow  from  adhering  oxide  of  iron.  Ammonia  dis- 
solves it  easily,  and  without  residue,  a  character  which  distin- 
guishes this  oxide  from  the  protoxide  of  tin,  the  latter  being 
insoluble,  or  nearly  so,  in  that  menstruum.  Sesquioxide  of 
tin  is  dissolved  by  concentrated  hydrochloric  acid ;  the  taste 
of  the  solution  is  not  metallic.  It  is  distinguished  from  a  salt 
of  the  bioxide  of  tin,  by  producing  the  purple  precipitate  with 
chloride  of  gold.  A  sesquisulphide  exists,  corresponding  with 
this  oxide.  The  salts  of  sesquioxide  of  tin  have  not  been 
examined. 

Bioxide  of  tin,  Stannic  oxide,  SnOj,  74*82  or  935-25.  — This 
constitutes  the  common  ore  of  tin,  which  is  generally  crystal- 
lised. The  crystals  oi  tin-stone  are  sometimes  brownish-yellow 
and  translucent,  at  other  times  dark  brown  and  almost  black, 
and  contain  small  quantities  of  the  protoxides  of  iron  and 
manganese.  Their  primitive  form  is  an  obtuse  octohedron 
with  a  square  base ;  their  density  from  6*92  to  6*96.  Bioxide 
of  tin  in  this  state  does  not  dissolve  in  acids,  unless  previously 
ignited  with  an  alkali.  Anhydrous  stannic  oxide  may  be  ob- 
tained in  colourless  crystals  derived  from  a  right  rhomboi'dal 
prism,  which  scratch  glass,  and  have  a  density  of  5 '72,  by  de- 
composing vapour  of  bichloride  of  tin  with  water  at  a  red  heat. 
These  crystals  are  isomorphous  with  one  of  the  native  varieties 
of  titanic  acid  (brookite),  whereas  the  crystals  of  native  tin- 


BIOXIDE    OF    TIN.  137 

stone  are  isomorphous  with  another  variety  of  titanic  acid 
(rutile) . 

Bioxide  of  tin  is  susceptible  of  two  modifications  called 
stannic  and  metastannic  acid,  distinguished  from  one  another 
by  the  proportions  of  water  and  metallic  oxide  with  which 
they  combine. 

Stannic  acid,  or  Hydrated  stannic  oxide,  SnOg.HO,  is  ob- 
tained by  decomposing  bichloride  of  tin  with  water,  or  by 
precipitating  a  soluble  stannate  with  an  acid.  It  is  white, 
gelatinous,  insoluble  in  water,  but  dissolves  readily  in  dilute 
acids.  A  moderate  heat  converts  it  into  metastannic  acid. 
At  a  red  heat,  it  gives  off  all  its  water,  and  becomes  very  hard. 

Solutions  of  stannic  oxide  in  acids  (the  hydrated  bichloride 
for  example),  are  decomposed  by  zinc  and  cadmium,  the  tin 
being  precipitated  in  an  arborescent  form.  Hydro  sulphuric 
acid  and  sulphide  of  ammonium  throw  down  the  yellow  bisul- 
phide soluble  in  alkalies  and  in  sulphide  of  ammonium.  Am- 
monia throws  down  a  white  bulky  hydrate,  soluble  with  some 
turbidity  in  a  large  excess  of  ammonia.  The  presence  of 
tartaric  acid  prevents  the  precipitation.  Potash  throws  down 
a  white  bulky  hydrate  (probably  containing  potash),  easily 
soluble  in  excess.  Carbonate  of  potash  gives  a  white  precipi- 
tate, consisting,  according  to  Fremy,  of  stannate  of  potash, 
which  dissolves  in  excess  of  the  reagent,  but  separates  com- 
pletely after  a  while.  Bicarbonate  of  potash  and  sesquicar- 
bonate  of  ammonia  throw  down  the  hydrated  oxides,  insoluble 
in  excess  of  the  reagent.  Chloride  of  gold  gives  no  preci- 
jiitate  with  stannic  salts. 

All  salts  of  tin  are  easily  reduced  to  the  metallic  state  when 
heated  on  charcoal  before  the  blowpipe  with  carbonate  of  soda 
or  cyanide  of  potassium. 

The  compounds  of  stannic  acid  with  bases  are  represented 
by  the  general  formula  MO.SnOg.  The  stannates  of  the 
alkalies  crystallise  readily,  and  may  be  obtained  in  the  anhy- 
drous state.     They  are  prepared  by  dissolving  stannic  acid  in 


138  TIN. 

alkalies,  or  by  calcining  metastannic  acid  or  the  metastannates 
in  contact  with  an  excess  of  base.  Siannate  of  potash,  KO . 
Sn02  +  4HO,  is  white,  very  soluble  in  water,  insoluble  in 
alcohol ;  it  crystallises  in  oblique  rhombo'idal  prisms,  which 
are  transparent,  sometimes  very  large,  and  slowly  absorb 
moisture  fi'om  the  air.  It  has  a  caustic  taste  and  strong  alka- 
line reaction.  Water  appears  to  decompose  it  after  a  while 
into  potash  and  metastannate  of  potash.  It  is  precipitated 
from  its  solution  by  nearly  all  soluble  salts,  even  by  those 
of  potash,  soda  and  ammonia.  Stannate  of  soda,  NaO.SnOj 
+  4HO,  resembles  the  potash- salt,  and  is  obtained  in  a  similar 
manner.  It  crystallises  in  hexagonal  tables,  dissolves  in  cold 
more  readily  than  in  hot  water,  is  insoluble  in  alcohol,  and 
has  a  strong  alkaline  reaction  (Fremy). 

The  stannatcs  of  all  other  bases  are  insoluble  in  water,  and 
may  be  formed  by  double  decomposition.  The  scsquioxide  of 
tin  may  be  regarded  as  a  stannate  of  stannous  oxide,  SuO.SnOj 
(Fremy). 

Metastannic  acid,  Sn^OiQ. — Tin  treated  with  strong  nitric 
acid  is  completely  transformed  into  a  white  powder,  which, 
when  dried  in  the  air  at  ordinary  temperatures,  contains 
SngOiQ.lOHO  ;  after  being  heated  for  some  time  to  212°,  it  is 
reduced  to  SujOio-SHO.  It  is  white,  cr\^stalline,  insoluble  in 
water,  and  in  dilute  nitric  acid  and  sulphuric  acid.  Monohy- 
drated  sulphuric  acid  dissolves  it  in  considerable  quantity, 
forming  a  compound  which  is  not  decomposed  by  water  or 
alcohol.  It  dissolves  in  dilute  hydrochloric  acid,  forming  a 
liquid,  which,  when  treated  with  excess  of  acid,  yields  a  white 
amorphous  precipitate,  differing  considerably  from  hydrated 
bichloride  of  tin.  Metastannic  acid  also  combines  with  certain 
organic  acids.  The  acid  prepared  with  nitric  acid  is  completely 
insoluble  in  ammonia,  but  when  dissolved  in  potash  and  pre- 
cipitated by  an  acid,  it  becomes  gelatinous  and  soluble  in 
ammonia ;  in  that  state,  it  contains  more  water  than  in  the 
crystalline  state ;  but  by  the  slightest  desiccation,  or  even  by 


STANNIC    COMPOUNDS.  139 

boiling  for  a  few  minutes,  it  gives  up  part  of  its  water,  and  is 
reconverted  into  the  modification  insoluble  in  ammonia.  Other 
hydrates  of  metastannic  acid  appear  also  to  exist,  possessing 
different  properties. 

The  metastannates  are  represented  by  the  general  formula 
(M0.4H0.)  SugOiQ.  They  can  only  exist  in  the  hydrated 
state,  being  decomposed  when  deprived  of  their  basic  water. 
The  potash  and  soda-salts,  heated  with  excess  of  base,  are 
transformed  into  stannates.  They  are  soluble  in  basic  water. 
The  other  metastannates  are  insoluble,  and  are  obtained 
by  double  decomposition.  Metastannate  of  potash,  (K0.4H0). 
Sn^OjQ,  is  prepared  by  dissolving  metastannic  acid  in  cold 
potash ;  it  may  be  precipitated  in  the  solid  state  by  adding 
pieces  of  potash  to  the  liquid.  It  is  gummy,  uncrystallisable, 
and  strongly  alkaline.  At  a  red  heat,  it  gives  off  its  water 
and  is  decomposed ;  the  calcined  mass,  digested  in  water,  yields 
up  all  its  alkali  and  leaves  insoluble  metastannic  acid.  The 
soda-salt,  (Na0.4HO).Sn50io,  closely  resembles  the  potash- 
salt,  but  is  crystalline,  dissolves  slowly  in  water,  and  is  decom- 
posed by  boiling  water.  Metastannate  of  stannous  oxide, 
(Sn0.4HO).Sn50io,  is  obtained  by  placing  metastannic  acid 
in  contact  with  protochloride  of  tin.  It  is  yellow,  and  in- 
soluble in  water ;  when  heated  in  contact  with  the  air,  it  is 
transformed  into  anhydrous  stannic  acid  (Fremy). 

Oxide  of  tin  is  employed  in  the  preparation  of  the  white 
glass  known  as  enamel ;  and  the  ignited  and  finely  levigated 
oxide  forms  jeioeller's  putty,  which  is  used  in  polishing  hard 
objects.  The  hydrated  oxide  resembles  alumina  in  forming 
insoluble  compounds  with  the  organic  colouring  matters;  hence 
its  salts  are  much  prized  as  mordants. 

Bisulphide  of  tin,  Stannic  sulphide,  SnS2,  is  precipitated  from 
stannic  salts,  of  a  dull  yellow  colour,  by  hydrosulphuric  acid 
gas.  Prepared  in  the  dry  way,  by  igniting  a  mixture  of  stannic 
oxide,  sulphur,  and  sal-ammoniac  in  a  covered  crucible,  it 
forms  the  aurum  musivum  or  mosaic  gold  of  the  alchemists.  In 


140  TIN. 

this  operation,  tlie  sal- ammoniac  is  indispensable,  although  it 
seems  to  serve  no  other  purpose  than  to  prevent  the  elevation 
of  temperature  which  results  from  the  sulphuration.  Mosaic 
gold  when  well  prepared  has  the  yellow  colour  of  gold,  and  con- 
sists of  brilliant  translucent  scales,  which  are  soft  to  the  touch. 
No  acid  dissolves  it,  except  aqua-regia.  It  is  decomposed  by 
dry  chlorine,  yielding  the  compound  SnCl2.SCl2. 

Bichloride  of  tin,  Permuriate  of  tin,  Stannic  chloride,  SnCl2 ; 
129'82  or  162275. — The  anhydrous  bichloride  of  tin,  known 
as  the  fuming  liquor  of  Libavius,  is  procured  by  distilling,  at 
a  gentle  heat,  a  mixture  of  4  parts  of  corrosive  sublimate  and 
1  part  of  tin  in  filings,  or  tin  amalgamated  with  a  little 
mercury,  and  then  reduced  to  powder.  A  colourless,  highly 
limpid  liquid  is  found  in  the  condenser,  which  fumes  strongly 
in  humid  air.  The  bichloride  boils  at  218°;  the  density  of 
its  vapour,  observed  by  Dumas,  is  9*  1997.  It  forms  a  solid 
saline  mass  with  one  third  of  its  weight  of  water,  and  dissolves 
in  a  larger  quantity  of  water.  The  same  salt  is  obtained  in 
solution,  by  conducting  a  stream  of  chlorine  gas  into  a  strong 
solution  of  the  protochloride  of  tin,  till  the  latter  is  saturated, 
which  is  shown  by  the  solution  ceasing  to  precipitate  mercury 
from  a  solution  of  corrosive  sublimate.  A  solution  of  this  salt 
extensively  used  in  dyeing,  and  known  as  the  nitromuriate  of 
tin,  is  generally  prepared  by  oxidising  crystallised  protochloride 
of  tin  with  nitric  acid ;  or  by  dissolving  tin  in  a  mixture  of 
hydrochloric  and  nitric  acids,  avoiding  any  considerable  eleva- 
tion of  temperature. 

Ammonio-bichloride  of  tin,  SnClj.NHg  or  (NH3Sn)Cl2. — An- 
hydrous bichloride  of  tin  absorbs  ammoniacal  gas,  and  forms  a 
white  powder,  which  may  be  sublimed  without  decomposition ; 
after  sublimation  it  is  entirely  soluble  in  water  (Rose). 

Chlorosulphide  of  tin,  SnS2.2SnCl2.  —  Hydrosulphuric  acid 
gas  is  rapidly  absorbed  by  bichloride  of  tin,  with  formation  of 
hydrocliloric  acid  gas ; 

SSnCla  +  2HS  =  SnS2.2SnCl2  +  2HC1. 


ALLOYS    or    TIN.  141 

The  compound  obtained  by  perfect  saturation  with  hydro- 
sulphuric  acid  is  a  yellowish  or  reddish  liquid^  heavier  than 
water.  When  heated^  it  gives  off  bichloride  of  tin,  and  leaves 
the  bisulphide  (Dumas). 

Bichloride  of  tin  and  sulphur,  SnCl2.2SCl2.  —  Formed  by 
the  action  of  chlorine  gas  on  bisulphide  of  tin  at  ordinary 
temperatures : 

SnS2  +  6C1  =  SnCl2.2SCl2. 

Large  yellow  crystals,  which  fuse  when  heated,  and  sublime 
without  decomposition ;  they  fame  in  the  air  more  strongly 
than  the  bichloride. 

Bichloride  of  tin  with  Pentachloride  of  phosphorus,  2SnCl2. 
PCI5.  — When  a  mixture  of  the  last-described  compound  with 
terchloride  of  phosphorus  is  moderately  heated  in  a  stream  of 
hydrochloric  acid  gas,  a  rapid  action  takes  place,  and  this 
compound  is  formed,  together  with  other  products : 

2(SnCl2.2SCl2)  +  3PCI3  =  2SnCl2.PCl5  +  2PCI5  +  2S2CI. 
If  the  retort  in  which  the  action  takes  place  is  connected 
with  a  receiver  surrounded  with  ice,  a  pasty,  yellomsh  mass 
collects  in  the  receiver,  and  an  amorphous  white  body  remains 
in  the  retort.  On  heating  the  yellowish  mass  to  between 
212°  and  250°,  dichloride  of  sulphur  escapes,  and  there  re- 
mains a  mixture  of  pentachloride  of  phosphorus  with  the 
double  chloride,  identical,  in  fact,  with  the  amorphous  white 
mass  in  the  retort.  On  heating  this  mixture  to  a  tempe- 
rature between  284°  and  320°,  the  pentachloride  of  phosphorus 
is  also  driven  off,  leaving  the  double  chloride,  which  sublimes 
between  392°  and  428°,  in  highly  lustrous  colourless  needles, 
which,  however,  soon  crumble  to  an  amorphous  powder,  even 
when  kept  in  close  vessels.  The  compound  fumes  strongly 
in  the  air,  and  rapidly  absorbs  water,  being  thereby  converted 
into  transparent  colourless  crystals  containing  water  of  crys- 
tallisation.* 

*  Casselmann,  Ann.  Cli.  Pharm.  Ixxxiii.  257. 


142  ALLOYS    OF    TIN. 

Bichloride  of  tin  toith  Oxy chloride  of  phosjjhorus,  2SnCl2 
+  PO2CI3.  —  Obtained  by  the  action  of  oxychloridc  of  phos- 
phorus on  bichloride  of  tin :  if  an  excess  of  either  substance 
is  present,  the  compound  separates  in  large  isolated  crystals. 
It  has  a  peculiar  odour,  melts  at  131°,  and  boils  at  356°,  and 
distils  without  alteration  if  kept  from  contact  with  moist  air. 
It  fumes  in  the  air  and  is  decomposed  by  water.  When 
oxychloride  of  phosphorus  comes  in  contact  in  a  close  vessel 
with  the  compound  SnCl2.2SCl2,  the  whole  dissolves,  forming 
a  yellowish  liquid,  from  which,  after  a  while,  the  compound 
2SnCl2 .  PO2CI3  crystallises;  and  above  the  crystals  there 
remains  a  yellow  liquid,  probably  SCI2  (Casselmann) . 

Bichloride  of  tin  ivith  Phosphuretted  hydrogen,  3SnCl2.PH3. 
' —  These  two  bodies  unite  without  production  of  hydi'ochloric 
acid;  the  compound  is  solid  (Rose). 

Bichloride  of  tinwithpotassiuin,  SnCl2.KCl.  —  The  solution 
of  bichloride  of  tin,  when  mixed  with  an  equivalent  quantity 
of  chloride  of  potassium  and  evaporated,  yields  this  double 
salt  in  anhydrous  regular  octohedrons  having  a  vitreous  lustre. 
A  similar  double  salt  is  formed  with  chloride  of  ammonium. 

A  sulphate  and  nitrate  of  dioxide  of  tin,  have  been  crystal- 
lised ;  this  base  forms  no  carbonate. 

Both  the  sulphide  and  bisulphide  of  tin  act  as  sulphur-acids, 
combining  with  alkaline  sulphide.  The  bisulphide  of  tin 
dissolves  with  digestion  in  sulphide  of  sodium,  and  the  con- 
centrated solution  yields  fine  crystals  of  the  salt,  2NaS.SnS2 
+  12H0.  By  gradually  adding  tin  to  melted  pentasulphide 
of  sodium,  treating  the  resulting  mass  with  water,  and  then 
filtering  and  evaporating,  yellowish  octohedral  crystals  are 
obtained,  containing  NaS.SnSj  +  2H0.*  The  bisulphide 
of  tin  is  found  combined  with  the  subsulphides  of  copper 
and  iron,  forming  tin  pyrites,  a  rare  mineral,  2Fe2S.SnS2 
4-  2Cu2S.SnS2. 

Alloys  of  tin.  —  Tin  alloyed  with  small  quantities  of  anti- 

♦  Kiihn,  Pogg.  Ann.  Ixxxv.  293. 


ALLOYS    or    TIN.  143 

mony,  copper,  and  bismuth,  forms  the  best  kind  of  pewter, 
possessing  the  peculiar  whiteness  of  metallic  tin.  The 
most  fusible  compound  of  tin  and  bismuth  is  that  of  an  atom 
of  each  metal,  Bi.Sn;  it  melts  at  289*4°  (Rudberg).  When 
the  metals  are  mixed  in  other  ratios,  a  portion  first  congeals 
at  a  higher  temperature,  separating  from  the  compound 
mentioned,  which  remains  liquid  till  the  temperature  falls  to 
289*4°.  Although  tin  precipitates  copper  from  its  solutions 
in  acids,  yet  it  is  possible  to  precipitate  tin  upon  copper,  and 
to  cover  the  latter  with  tin,  as  is  proved  by  the  tinning  of 
pins.  Tin  is  dissolved  in  a  mixture  of  1  part  of  bitartrate  of 
potash,  2  of  alum,  2  of  common  salt,  and  a  certain  quantity  of 
water,  and  the  pins  which  consist  of  brass  wire  are  introduced 
at  the  boiling  temperature.  The  pins  undergo  no  change  in 
this  liquor,  supposing  it  to  contain  no  undissolved  tin,  but 
the  moment  a  fragment  of  tin  touches  the  pins,  all  those  in 
contact  with  each  other  are  tinned.  Dr.  Odlings  finds  that 
pure  copper  boiled  in  a  moderately  dilute  and  rather  acid 
solution  of  stannous  chloride,  also  becomes  coated  with  tin.* 

ESTIMATION    OF   TIN,    AND    METHODS    OF    SEPARATING    IT    FROM 
THE    PRECEDING    METALS. 

Tin  is  estimated  in  the  state  of  bioxide,  a  compound  which 
contains  78-62  per  cent,  of  the  metal.  If  the  tin  is  united 
with  other  metals  in  the  form  of  an  alloy,  the  alloy  must  be 
treated  with  nitric  acid  of  sp.  gr.  about  1-3.  The  tin  is  then 
converted  into  bioxide,  while  the  other  metals  (with  the  ex- 
ception of  antimony)  are  dissolved  by  the  acid.  The  oxide 
of  tin  must  then  be  thoroughly  washed,  afterwards  dried, 
ignited,  and  weighed.  To  insure  complete  oxidation,  the 
alloy  should  be  finely  divided. 

When  the  tin  is  in  solution  in  hydrochloric  acid  (which  is 
its  usual  solvent)  it  must  first  be  precipitated  as  a  stdphide 

*  Chem.  Soc.  Qu.  J.  ix.  291. 


144  ALLOYS    OF    TI\. 

by  hydrosulplmric  acid,  and  tlie  sulphide  then  converted 
into  bioxide  by  roasting  in  an  open  porcelain  crucible_,  a  small 
quantity  of  nitric  acid  being  added  to  insure  complete  oxida- 
tion. 

Precipitation  by  hydrosulphuric  acid  serves  also  to  separate 
tin  from  all  metals  which  are  not  thrown  down  by  that 
reagent  from  their  acid  solutions. 

From  cadmium,  copper,  and  lead,  tin  may  be  separated  by 
treating  the  solution  with  a  slight  excess  of  ammonia,  and 
then  adding  sulphide  of  ammonium  containing  excess  of  sul- 
phur. All  the  metals  are  thereby  converted  into  sulphides, 
but  the  sulphide  of  tin  dissolves,  while  the  others  are  left 
undissolved. 

Volumetric  estimation  of  tin.  —  The  following  method  of 
estimating  the  amount  of  tin  in  the  commercial  protochloride 
is  given  by  Dr.  Penny* ;  it  is  basecl  on  the  conversion  of  proto- 
chloride of  tin  into  bichloride  by  the  action  of  chromic  acid 
in  presence  of  free  hydrochloric  acid  : 

3SnCl  +  K0.2Cr03  -f  7HC1  =  SSnCla  H  KCl  +  Cr^Clg  +  7H0. 

The  solution  of  the  tin-salt  is  mixed  with  a  sufficient  quantity 
of  hydrochloric  acid  and  gently  heated,  and  a  solution  of 
bichromate  of  potash  gradually  added,  till  a  drop  of  the  liqui  d 
added  to  acetate  of  lead  (a  solution  of  1  part  of  that  salt  in 
8  parts  of  water  being  scattered  in  large  drops  on  a  porcelain 
plate)  produces  a  faint  yellow  colour ;  or  tiU  the  liquid  pro- 
duces a  dark  broAvn  or  red  colouring  in  an  acidulated  mixture 
of  sulphocyanide  of  potassium  and  a  pure  protosalt  of  iron. 
With  the  commercial  solution  of  the  protochloride  of  tin,  the 
contrary  method  is  adopted;  that  is  to  say,  the  tin  solution, 
diluted  and  reduced  to  a  definite  volume,  is  poured  into  a  so- 
lution of  bichromate  of  potash  containing  a  known  weight  of 
that  salt.  Penny  finds,  by  direct  experiments,  that  83*2  parts 
of  pure  bichromate  of  potash  correspond  to  ICO  parts  of  tin. 

*  Chem.  Soc.  Qii.  J.  iv.  249, 


TITANIUM.  1J5 

SECTION    II. 

TITANIUM. 

Eq.  24-33  or  3037;  Ti. 

This  metal  was  discovered  in  1791,  by  Mr.  Gregor  of  Corn- 
wall, and  afterwards  by  Klaprotb,  who  gave  it  tlie  name 
titanium.  In  the  form  of  titanic  acid  it  constitutes  several 
minerals,  as  rutile,  anatase,  menachanite,  &c. ;  and  as  titanate 
of  protoxide  of  iron,  it  forms  ilmenite  and  other  species. 

When  titaniferous  iron-ores  are  smelted  in  the  blast  furnace, 
small  cubic  crystals  of  a  bright  copper  colour  are  found  on 
the  slag  which  adheres  to  the  lower  part  of  the  furnace. 
These  crystals  were  long  supposed  to  be  metallic  titanium ; 
but  Wohler*  has  shown  that  they  also  contain  carbon  and 
nitrogen,  being,  in  fact,  a  compound  of  cyanide  of  titanium 
with  nitride  of  titanium,  CyTi.SNTig.  Pure  titanium  is 
obtained  by  heating  the  double  fluoride  of  potassium  and 
titanium  with  potassium  in  a  covered  crucible.  The  metal  is 
then  set  free  with  vivid  incandescence,  and  the  fluoride  of 
potassium  may  be  removed  by  washing  with  water.  Titanium 
thus  obtained  is  a  dark  green,  heavy,  amorphous  powder, 
which  does  not  exhibit  any  shade  of  copper  colour,  even  after 
pressure ;  under  the  microscope  it  appears  as  a  cemented  mass, 
having  the  colour  and  lustre  of  iron.  Metallic  titanium  is 
also  obtained  by  mixing  titanic  acid  with  one-sixth  of  its 
weight  of  charcoal  and  exposing  it  to  the  strongest  heat  of  a 
wind-furnace.  It  was  thus  obtained  in  the  form  of  a  copper- 
coloured  or  gold- coloured  powder  by  Vauquelin,  Lampadius, 
and  others ;  but  possibly  the  charcoal  which  they  used  may 
have  contained  nitrogen,  and  that  element  united  with  the 
reduced  metal. 

*  Ann.  Ch.  Pbarra.  Ixxiii.  34. ;  Chem.  Soc.  Qu.  J.  ii.  352. 
VOL.  II.  L 


1  10  TITANIUM. 

Pure  titanium  (prepared  from  the  double  fluoride)  burns 
with  great  splendour  when  heated  in  the  air,  and,  if  sprinkled 
into  a  flame,  is  consumed,  with  brilliant  scintillations,  at  a 
considerable  distance  above  the  point  of  the  flame.  When 
heated  to  redness  in  oxygen-gas,  it  bums  with  a  splendour 
resembling  a  discharge  of  electricity.  In  chlorine-gas  it 
exhibits  similar  phenomena,  requiring  also  the  aid  of  heat  to 
set  it  on  fire.  Mixed  with  red  lead  and  heated,  it  bums  with 
such  violence  that  the  mass  is  thrown  out  of  the  vessel,  with 
loud  detonation.  Titanium  does  not  decompose  water  at 
ordinary  temperatures,  but  on  heating  the  water  to  the  boiling 
point,  hydrogen  begins  to  escape.  Warm  hydrochloric  acid 
dissolves  titanium  with  brisk  evolution  of  hydrogen.  Ammonia 
added  to  the  solution  throws  down  a  black  oxide ;  and,  on 
heating  the  liquid,  hydrogen  is  evolved,  and  the  precipitate  first 
turns  blue,  and  is  afterwards  converted  into  white  titanic 
acid. 

Titanium  forms  three  compounds  with  oxygen  :  viz.  the 
protoxide,  TiO,  whose  composition  is,  however,  doubtful ;  the 
sesquioxide,  Ti203 ;  and  titanic  acid,  TiOg. 

Protoxide  of  titanium,  TiO,  32-33.  or  403-7  — Is  formed 
when  titanic  acid  is  exposed  in  a  charcoal  crucible,  to  the 
highest  temperature  of  a  wind-furnace.  Where  the  acid  was 
in  contact  with  the  charcoal,  a  thin  coating  of  metallic  titanium 
is  formed  ;  but  within,  it  is  changed  into  a  black  mass,  which 
is  insoluble  in  all  acids,  and  not  otherwise  affected  by  them, 
and  is  oxidated  with  difficulty  when  heated  in  contact  with  air, 
or  by  fusion  with  nitre.  Protoxide  of  titanium  is  also  obtained 
by  the  moist  way,  in  the  form  of  a  deep  purple  powder,  when 
a  fragment  of  zinc  or  iron  is  introduced  into  a  solution  of 
titanic  acid  in  hydrochloric  acid ;  but  it  alters  so  quickly  by 
absorption  of  oxygen,  that  no  opportunity  has  yet  been  ob- 
tained of  studying  its  properties.  The  composition  assigned 
to  it  above  is,  therefore,  hypothetical.     The  blue  powder  is, 


OXIDES    or    TITANIUM.  147 

perhaps,  a  compound  of  protoxide  of  titanium  with  oxide  of 
zinc  or  iron. 

Sesquioxide  of  titanium,  Ti203. — When  anhydrous  titanic 
acid  is  strongly  ignited  in  a  current  of  hydrogen  gas,  it  be- 
comes black  and  loses  considerably  in  weight.  From  a  deter- 
mination of  the  actual  loss  of  weight,  Ebelmen  concludes  that 
sesquioxide  of  titanium  is  produced.  The  residue  is  not  acted 
upon  by  nitric  or  hydrochloric  acid,  but  dissolves  in  sulphuric 
acid,  forming  a  violet  solution.  * 

Titanic  acid,  Ti02,  40*33  or  503" 7.  —  In  the  mineral  rutile, 
titanic  acid  is  crystallised  in  the  form  of  tinstone,  the  link  by 
which  tin  is  connected  with  titanium.  Again,  ilmenite  and 
other  varieties  of  titanate  of  iron,  reO.Ti02  are  isomorphous 
with  sesquioxide  of  iron ;  and  thus  tin  comes  to  be  con- 
nected through  titanium  with  the  last  order  of  metals.  But 
titanic  acid  is  dimorphous,  and  crystallises,  in  anatase,  in 
an  unconnected  form.  The  best  method  of  obtaining  pure 
titanic  acid  is  to  fuse  titanate  of  iron,  reduced  to  powder  and 
levigated  with  sulphur.  The  sulphur  has  no  action  upon  the 
titanic  acid,  but  converts  the  protoxide  of  iron  into  a  sulphide 
of  iron,  which  is  dissolved  by  hydrochloric  acid.  If  iron  is 
still  retained  by  the  titanic  acid,  the  latter  is  heated  in  a  stream 
of  hydrosulphuric  acid  gas,  by  which  every  particle  of  iron  is 
converted  into  sulphide,  and  then  removed  by  hydrochloric 
acid. 

Titanic  acid  is  a  white  powder,  which  acquires  a  yellow 
tint  by  exposure  to  a  high  temperature ;  it  is  infusible  and 
insoluble  in  water.  Titanic  acid  is  considerably  analogous  in 
properties  to  silica ;  like  that  acid  it  has  a  soluble  modifica- 
tion, formed  by  igniting  titanic  acid  with  an  alkaline  car- 
bonate, which  is  soluble  in  dilute  hydrochloric  acid.  The  acid 
solution  of  titanic  acid  gives  an  orange-red  precipitate  with  an 
infusion  of  gall-nuts,  which  is  characteristic  of  titanic  acid. 

«  Ann.  Cli.  Phys.  [3.]  xx.  385. 
L  2 


118  TITANIUM. 

On  neutralising  the  acid  solution  with  ammonia,  the  soluble 
modification  of  titanic  acid  is  thrown  down  as  a  white  gela- 
tinous precipitate.  When  this  precipitate  is  dried  and  heated, 
it  glows,  and  the  titanic  acid  is  then  no  longer  soluble  in 
acids.  When  a  solution  of  bichloride  of  titanium,  or  of  the 
sulphate  of  titanic  acid  in  water,  is  boiled  for  some  time, 
titanic  acid  precipitates  in  the  insoluble  modification. 

Titanic  acid  mixed  with  borax,  or  better  with  phosphorus-salt, 
forms  in  the  outer  blowpipe-flame  a  colourless  glass,  but  in 
the  inner  flame,  a  glass  which  is  yellow  while  hot,  but  assumes 
a  violet  colour  on  cooling.  The  same  character  is  exhibited 
by  those  salts  of  titanic  acid  whose  bases  do  not  themselves 
impart  any  colour  to  the  bead.  If  the  titanic  acid  contains 
iron,  the  colour  of  the  bead  is  brown-red  or  blood-red  instead 
of  violet.  Many  titanates  yield  the  blue  colour  only  with 
phosphorus- salt,  not  with  borax.  The  colour  is  produced 
more  readily  by  heating  the  substance  on  charcoal  than  on 
platiimm  wire.  The  above  characters  suffice  to  distinguish 
titanic  acid  from  all  other  substances. 

Bisulphide  of  titanium,  TiS2,  was  discovered  by  Rose,  who 
formed  it  by  passing  the  vapour  of  bisulphide  of  carbon  over 
titanic  acid,  in  a  porcelain  tube  maintained  at  a  bright  red  lieat. 

Bichloride  of  titanium,  TiCl2,  was  formed  by  Mr.  George  of 
Leeds,  by  transmitting  chlorine  over  metallic  titanium  at  a 
red  heat.  It  is  a  transparent  colourless  liquid,  resembling 
bichloride  of  tin,  and  boiling  a  little  above  212°.  The  density 
of  its  vapour  is  0-615  (Dumas).  Bichloride  of  titanium 
combines  with  ammonia,  and  forms  a  white  saline  mass, 
TiCl2.2NH3.  Metallic  titanium  is  most  easily  obtained  by 
heating  this  compound  to  redness.  Bichloride  of  titanium 
also  absorbs  phosphurctted  hydrogen,  and  forms  a  dry  brown 
powder.  From  this  compound  when  heated,  a  lemon-yellow 
sublimate  rises,  which  Rose  found  to  contain  3  atoms  of  bi- 
chloride of  titanium,  combined  with  1  atom  of  a  compound  of 
phosphurctted  hydrogen  and  hydrochloric  acid,  analogous  to 


NITRIDES    OF    TITANIUM.  149 

sal-ammoniac,  but  wliich  could  not  be  isolated.  Bichloride  of 
titanium  combines  with  the  alkaline  chlorides,  forming  double 
salts,  which  are  colourless  and  capable  of  crystaUising.  It  also 
combines  with  chloride  of  cyanogen,  forming  a  yellow  crystal- 
line compound  containing  CyCl .  2TiCl2,  and  with  anhydrous 
hydrocyanic  acid,  forming  the  compound  HCy .  TiCl2,  a  yellow 
pulverulent  substance  which  sublimes  below  Ji]2°,  in  trans- 
parent, shining,  lemon-yellow  ci'ystals. 

Bromide  of  titanium^  TiBr2,  is  obtained  by  passing  bromine 
vapour  over  an  intimate  mixture  of  titanic  acid  and  carbon, 
heated  to  bright  redness,  and  distilling  the  resulting  brown 
liquid  with  excess  of  mercury  to  remove  free  bromine.  It  is 
an  amber-yellow  crystalline  body  of  specific  gravity  2*6.  It 
melts  at  102°,  and  boils  at  356°.  It  attracts  moisture  with 
the  greatest  avidity,  and  is  converted  into  titanic  and  hydro- 
bromic  acids  (F.  B.  Duppa). 

A  volatile  bifluoride  of  titanium,  TiF2,  was  obtained  by 
Unverdorben,  by  distilling  titanic  acid  in  a  platinum  ap- 
paratus with  fluor  spar  in  powder  and  fuming  sulphuric  acid. 

A  definite  sulphate  of  titanic  acid,  Ti02  .  SO3,  is  obtained 
by  dissolving  titanic  acid  in  sulphuric  acid,  and  evaporating 
to  dryness  at  a  heat  below  redness. 

Nitrides  of  titanium. — H.  Bose,  by  heating  the  double 
chloride  of  titanium  and  ammonium  in  ammoniacal  gas,  or 
by  heating  the  ammonio-chloride  of  titanium,  2NH3  .  TiClg, 
with  sodium,  obtained  a  copper-coloured  substance  which  he 
supposed  to  be  metallic  titanium,  but  which  Wohler  has 
shown  to  consist  of  nitride  of  titanium,  Ti3N2,  or  more 
probably  TigN^  =  3TiN  .  Ti3N ;  it  contains  28  per  cent,  of 
nitrogen.  This  compound  is  redder  than  the  cubic  crystals 
of  the  blast-furnaces,  which  have  a  tinge  of  yellow.  Another 
nitride  of  titanium,  TiN,  is  produced  when  titanic  acid  is 
strongly  heated  in  a  stream  of  ammoniacal  gas.  Its  powder 
is  dark  violet  with  a  tinge  of  copper-colour ;  in  small  pieces 
it  exhibits  a  violet  copper-colour  and  metallic  lustre.    A  third 

L   3 


150  TITANIUM. 

nitride,  TigNg,  or  more  probably  2TiN  .  TigN,  is  formed  wben 
Rose's  titanium  is  subjected  to  tbe  action  of  a  stream  of 
hydrogen  at  a  strong  red  heat.  It  has  a  brassy  or  almost 
gold-yellow  colour  and  a  metallic  lustre.  It  is  also  obtained 
(mixed  however  with  carbon)  when  titanic  acid  is  heated  to 
redness  in  a  stream  of  cyanogen  gas  or  hydrocyanic  acid 
vapour;  no  cyanide  of  titanium  is  formed  in  this  reaction. 
All  these  three  nitrides  of  titanium  sustain  without  decompo- 
sition, a  temperature  at  least  equal  to  that  of  melting  silver. 
Mixed  in  the  state  of  powder  with  the  oxides  of  copper,  lead, 
or  mercury,  and  heated,  they  emit  a  lively  sparkling  flame, 
and  reduce  the  oxides  to  the  metallic  state.  When  fused 
with  hydrate  of  potash,  they  give  off  ammoniacal  gas 
(Wohler). 

Nitrocyanide  of  titanium,  C2NTi .  STigN.  —  This  is  the 
copper-coloured  compound  already  s2)oken  of  as  occurring 
in  the  iron  furnaces,  and  formerly  mistaken  for  metallic 
titanium.  Its  formation  appears  to  be  connected  with  that 
of  cyanide  of  potassium,  so  constantly  observed  in  the  blast- 
furnaces. It  sometimes  occurs  in  very  large  masses ;  in  a 
furnace  at  Rubeland  in  the  Ilartz,  a  mass  of  it  was  found, 
weighing  80  pounds.  This  compound  forms  cubic  crystals 
harder  than  quartz,  and  of  specific  gravity  5*3.  It  contains 
18  per  cent,  of  nitrogen  and  4  of  carbon.  In  its  chemical 
characters,  it  resembles  the  nitrides  just  described,  giving  off 
ammonia  when  heated  with  potash,  and  reducing  the  oxides 
of  lead,  copper,  and  mercury,  when  heated  with  them.  A 
similar  product  may  be  formed  by  placing  a  mixture  of  titanic 
acid  and  ferrocyanide  of  potassium  in  a  well  closed  crucible, 
and  exposing  it  for  an  hour  to  a  heat  sufl&cient  to  melt 
nickel.  (Wohler.) 


ESTIMATION    OF    TITANIUM.  J.51 


ESTIMATION  OF  TITANIUM,  AND  METHODS  OF  SEPARATING  IT  FROM 
THE  PRECEDING  METALS. 

Titanium  is  always  estimated  in  the  form  of  titanic  acid. 
This  compound  is  best  precipitated  from  its  solutions  in  acids 
by  ammonia,  which  throws  it  down  in  the  form  of  a  very  bulky 
precipitate,  resembling  hydrate  of  alumina.  A  great  excess 
of  ammonia  must  be  avoided,  as  it  would  redissolve  a  small 
portion  of  the  titanic  acid.  The  precipitate  after  ignition 
contains  60  per  cent,  of  titanium. 

If  the  titanic  acid,  after  precipitation  by  ammonia,  is 
to  be  redissolved  in  acids,  which  is  sometimes  necessary  in 
order  to  separate  it  from  other  metals,  great  care  must  be 
taken  in  the  precipitation  to  avoid  all  rise  of  temperature,  and 
the  precipitate  must  be  washed  with  cold  water,  because  heat 
has  the  effect  of  rendering  titanic  acid  more  or  less  insoluble 
in  acids. 

Titanic  acid  may  also  in  some  cases  be  separated  from  its 
acid  solutions  by  boiling ;  from  the  solution  in  sulphuric  acid, 
complete  precipitation  is  effected  by  this  method ;  but  when 
hydrochloric  acid  is  the  solvent,  a  small  portion  of  titanic  acid 
always  remains  in  solution  after  boiling. 

Protoxide  of  titanium  is  precipitated  from  its  solutions  by 
ammonia,  and  the  precipitate,  after  standing  from  24  to  36 
hours,  is  converted,  with  evolution  of  hydrogen,  into  titanic 
acid,  in  which  form  it  may  be  estimated. 

From  the  alkalies  and  alkaline  earths,  titanic  acid  may  be 
separated  by  ammonia,  the  solution  in  the  latter  case  being 
carefully  excluded  from  the  air.  Baryta  may  also  be  separated 
by  sulphuric  acid. 

Titanic  acid  is  separated  from  magnesia  by  boiling,  if  the 
two  are  dissolved  in  sulphuric  acid,  and  by  precipitation  with 
carbonate  of  baryta,  when  hydrochloric  acid  is  the  solvent. 

The  separation  from  alumina  and  glucina  is  also  effected  by 
boiling  the  sulphuric  acid  solution. 

L   4 


152  CHROMIUM. 

From  the  metals  which  are  precipitated  as  sulphides  by 
sulphide  of  ammonium,  viz. ,  manganese^  iron,  cobalt,  nickel,  and 
zinc,  titanic  acid  is  separated  by  mixing  the  acid  solution  with 
tartaric  acid  and  excess  of  ammonia  (which  then  forms  no 
precipitate),  and  adding  sulphide  of  ammonium,  which  pre- 
cipitates everything  but  the  titanic  acid.  The  filtered  solution 
is  then  evaporated  to  dryness,  and  the  residue  ignited  in  a 
platinum  crucible  to  expel  ammoniacal  salts  and  burn  away 
the  carbon  of  the  tartaric  acid.  As  this  carbonaceous  matter 
is  very  difficult  to  burn,  the  ignition  should  either  be  performed 
in  a  muffle  furnace,  or  a  stream  of  oxygen  should  be  very 
gently  directed  into  the  crucible.  The  residue  consists  of 
titanic  acid,  which  may  then  be  weighed. 

From  cadmium,  copper,  lead,  and  tin,  titanium  is  easily 
separated  by  hydrosulphuric  acid. 


SECTION     III. 

CHROMIUM. 

Eq.  26-8  or  335 ;  Cr. 

This  metal,  so  remarkable  for  the  variety  and  beauty  of  its 
coloured  preparations,  was  discovered  by  Yauquclin  in  17^7, 
in  the  red  mineral  now  known  as  chromate  of  lead.  It  has 
since  been  found  in  other  minerals,  more  particularly  chrome- 
iron  (FeO .  Cr203),  a  mineral  which  many  countries  possess 
in  considerable  quantity.  It  is  from  this  ore  that  the  com- 
pounds of  chromium,  used  in  the  arts,  are  actually  derived. 
The  metal  may  be  procured  by  the  reduction  of  its  oxide,  in 
the  usual  way;  but  the  reduction  is  as  difficult  as  that  of 
manganese.  Chromium  is  a  greyish-white  metal,  of  density 
5*9,  very  difficult  to  fuse,  and  not  magnetic.  It  does  not 
undergo  oxidation  in  the  air.  It  dissolves  in  hydrofluoric 
acid  with  evolution  of  hydrogen.     Chromium  is  also  obtained 


CHROMIC    OXIDE.  153 

as  a  brown  powder,  when  sesqnichloride  of  chromium  is 
heated  in  ammoniacal  gas  (Liebig). 

Chromium  forms  several  compounds  with  oxygen;  viz. 
jivotoxide  of  chromium,  or  chromous  oxide,  CrO,  isomorphous 
with  ferrous  oxide,  &c. ;  sesquioxide  of  chromium,  or  chromic 
oxide,  Cr203,  isomorphous  with  ferric  oxide  and  alumina ;  and 
chromic  acid,  CrOg,  isomorphous  with  sulphuric  acid ;  also  a 
chromosO'Ckromic  oxide,  Cr304,  or  CrO.Cr203,  and  four  oxides 
intermediate  between  chromic  oxide  and  chromic  acid,  which 
may,  in  fact,  be  regarded  as  chromates  of  chromic  oxide;  viz. 
monochromute  of  chromic  oxide,  or  Cr203.Cr03  =  Cr30g ;  the 
bichromate,  Cr203.2Cr03  =  Cr40g;  the  neutral  chromate, 
Cr203.3Cr03  =  Cr50i2,  and  the  acid  chromate,  Cr203.4Cr03 
=  CrgOis- 

Protoxide  of  chromium,  Chromous  oxide,  CrO  ;  34*8  or  435. 
— This  oxide  probably  exists  in  chrome-iron,  and  in  pyrope. 
It  is  precipitated  in  the  form  of  a  hydrate  by  the  action  of 
potash  on  a  solution  of  the  protochloride.  The  anhydrous 
protoxide  has  not  yet  been  obtained.  The  hydrate  is  very 
unstable,  decomposes  water,  even  at  ordinary  temperatures, 
and  if  the  air  be  not  excluded  by  filling  the  apparatus  with 
hydrogen,  is  converted,  almost  as  soon  as  formed,  into 
chromoso-chromic  oxide  Cr304,  with  evolution  of  hydrogen 
(Peligot).  It  is  yellow  when  recently  precipitated,  brown 
when  dry,  and  may  be  preserved  unaltered  in  dry  air.  When 
ignited  it  gives  off  hydrogen,  and  the  oxygen  thereby  liberated 
converts  the  remaining  protoxide  into  sesquioxide  (Moberg). 

Hydrated  chromous  oxide  is  insoluble  in  dilute  acids,  but 
dissolves  slowly  in  strong  acids.  The  chromous  salts  are  best 
prepared  by  mixing  a  solution  of  the  protochloride  with  the 
corresponding  potash  or  soda  salts,  access  of  air  being  carefully 
prevented.  They  are  generally  of  a  red  colour,  sometimes 
inclining  to  blue ;  dissolve  but  sparingly  in  cold  water,  but 
more  readily  in  hot  water.  Like  ferrous  salts,  they  dissolve 
large  quantities  of  nitric  oxide,  forming  dark  brown  solutions. 


154  CHROMIUM. 

Protochlonde  of  chromium,  Chromom  chloride,  CrCl ;  62*3 
or  778" 75. — Obtained  by  passing  hydrogen  gas  over  perfectly 
anhydrous  sesquichloride  of  cliromium  very  gently  heated,  as 
long  as  hydrocldoric  acid  gas  continues  to  escape.  The 
hydrogen  must  be  previously  freed  from  all  traces  of  oxygen 
by  passing  it  through  a  solution  of  protochloride  of  tin  in 
caustic  potash,  then  through  tubes  containing  sulphuric  acid 
and  chloride  of  calcium,  and  lastly  over  red-hot  metallic 
copper.  The  protochloride  is  also  formed  by  passing  dry 
chlorine  gas  over  a  red-hot  mixture  of  charcoal  and  chromic 
oxide.  The  first  method  yields  the  protochloride  in  the  form 
of  a  white,  velvety  substance,  retaining  the  form  of  the  sesqui- 
chloride from  which  it  has  been  formed ;  the  second  method 
yields  it  in  fine  while  crystals,  usually  mixed,  however,  with 
chromic  oxide,  chromic  chloride,  and  charcoal. 

Protochloride  of  chromium  dissolves  in  water,  with  evolution 
of  heat,  forming  a  blue  solution,  which  rapidly  turns  green 
when  exposed  to  the  air  or  to  chlorine  gas.  AVith  potash  it 
forms  a  dark  brown  precipitate  (yellow,  according  to  !Moberg, 
if  the  air  be  completely  excluded)  of  hydrated  chromous  oxide, 
which,  however,  quickly  changes  to  light  brown  chromoso- 
chromic  oxide,  with  evolution  of  hydrogen.  Ammonia  forms 
a  greenish  white  precipitate,  without  evolution  of  hydrogen. 
With  ammonia  and  sal-ammoiiiac,  a  blue  liquid  is  formed 
which  turns  red  on  exposure  to  the  air.  Sulphide  of  ammo- 
nium or  potassium  forms  a  black  precipitate  of  chromous 
sulphide.  The  solution  of  protochloride  of  chromium  is  one 
of  the  most  powerful  deoxidising  agents  known.  With  a  solu- 
tion of  monochromate  of  potash,  it  forms  a  dark  brown  preci- 
pitate of  chromoso-chromic  oxide,  which,  however,  disappears 
on  the  addition  of  an  excess  of  the  protochloride,  and  forms  a 
green  solution.  It  precipitates  calomel  from  a  solution  of 
corrosive  sublimate.  With  cupric  salts,  it  forms  at  first  a 
white  precipitate  of  cuprous  chloride ;  but  when  added  in  excess 
throws  down  red  cuprous  oxide.  It  instantly  converts  tungstic 


CHROMIC    OXIDE.  155 

acid  into  blue  oxide  of  tungsten,  and  precipitates  gold  from 
the  solution  of  the  chloride. 

Chromous  carbonate  is  formed  by  adding  a  solution  of  the 
chloride  to  carbonate  of  potash ;  its  precipitate  is  red  or  red- 
brown,  if  the  alkaline  solution  is  hot,  but  in  the  form  of 
dense  yellow  or  bluish  green  flakes,  if  it  is  cold ;  the  preci- 
pitate appears,  however,  to  have  the  same  composition  in  all 
cases  (Moberg). 

Chromous  sulphite  is  obtained  by  double  decomposition  in 
the  form  of  a  brick-red  precipitate,  which  becomes  bluish- 
green  on  exposure  to  the  air  (Moberg) . 

Chromous  sulphate. — When  the  metallic  powder  obtained 
by  treating  sesquichloride  of  chromium  with  potassium  is 
treated  with  dilute  sulphuric  acid,  hydrogen  is  evolved,  and  a 
solution  obtained  which  exhibits  the  characters  of  a  chromous 
salt  (Peligot). 

Chromoso-chromic  oxide ,  CrgO^  =  CrO  .  Cr203. — Formed 
when  the  protoxide  comes  in  contact  with  water,  and  conse- 
quently at  the  moment  of  its  precipitation  by  potash,  from  a 
solution  of  the  protochloride.  After  washing  with  water  and 
drying  in  vacuo,  it  has  the  colour  of  Spanish  tobacco.  It  is 
but  feebly  attacked  by  acids.  The  hydrate  is  composed  of 
Cr304  .  HO ;  when  heated,  it  is  converted  into  chromic  oxide 
with  evolution  of  hydrogen. 

Sesquioxide  of  chromium,  Chromic  oxide,  77*6  or  970.— This 
oxide  exists  in  chrome-iron,  but  is  not  immediately  derived 
from  that  mineral.  When  chromate  of  mercury,  the  orange 
precipitate  obtained  on  mixing  nitrate  of  mercury  and  chro- 
mate of  potash,  is  strongly  ignited,  chromic  oxide  remains  as 
a  powder  of  a  good  green  colour.  Chromic  oxide  is  also 
obtained,  by  deoxidising  the  chromic  acid  of  bichromate  of 
potash  in  various  ways ;  by  ignition  with  sulphur,  for  instance, 
or  by  igniting  together  1  part  of  bichromate  of  potash  with 
1-i-  parts  of  sal-ammoniac  and  1  part  of  carbonate  of  potash, 
whereby  chloride  of  potassium  and  sesquioxide  of  chromium 


156  CHROMIUM. 

are  formed,  the  chromic  acid  losing  half  its  oxygen,  which  is 
converted  into  water  by  the  hydrogen  of  the  ammonia. 
Another  process,  interesting  from  affording  the  oxide  in  the 
state  of  crystals,  is  to  pass  the  vapour  of  chlorochromic  acid 
(Cr02Cl)  through  a  tube  heated  to  whiteness,  when  oxygen 
and  chlorine  gases  are  disengaged,  and  chromic  oxide  attaches 
itself  to  the  surface  of  the  tube.  The  crystals  have  a  metallic 
lustre,  and  are  of  so  deep  a  green  as  to  appear  black ;  they 
have  the  same  form  as  specular  iron  ore,  a  density  of  5*21,  and 
are  as  hard  as  corundum  (Woliler).  The  ignited  oxide  is  not 
soluble  in  acids ;  heated  with  access  of  air,  and  in  contact 
with  an  alkali,  it  absorbs  oxygen  and  is  converted  into 
chromic  acid.  Fused  with  borax  or  other  vitreous  substances, 
scsquioxide  of  chromium  produces  a  beautiful  green  colour; 
it  is  the  colouring  matter  of  the  emerald,  and  is  employed  to 
produce  a  green  colour  upon  earthenware.  Scsquioxide  of 
chromium  (and  not  chromic  acid)  is  also  the  colouring  matter 
of  jnnk  colour  applied  to  stoneware.  This  substance  is  formed 
by  strongly  igniting  a  mixture  of  100  parts  of  bioxide  of  tin, 
33  parts  of  chalk,  and  not  more  than  one  part  of  scsquioxide 
of  chromium.* 

To  obtain  the  same  oxide  in  the  hydrated  state,  a  solution 
of  bichromate  of  potash  is  brought  to  the  boiling  point,  and 
hydrochloric  acid  and  alcohol  added  alternately  in  small 
quantities,  till  the  solution  passes  from  a  red  to  a  deep  green 
colour,  and  no  longer  effers'csces  from  escape  of  carbonic 
acid  gas,  on  addition  of  either  the  acid  or  alcohol.  In 
this  experiment,  the  chromic  acid  liberated  by  the  hydro- 
chloric acid,  is  deprived  of  half  its  oxygen  by  the  hydrogen 
and  carbon  of  the  alcohol,  and  the  resulting  scsquioxide  of 
chromium  is  dissolved  by  the  excess  of  hydrochloric  acid  pre- 

*  Malaguti,  Ann.  Ch.  Phys.  [3.]  Ixi.  p.  433.  Mr.  O.  Sims  finds  that 
sesquioxide  of  iron  and  bioxide  of  manganese  may  be  substituted  for  oxide  of 
chromium  in  pink  colour,  so  that  the  coloration  of  that  substance  is  of 
a  very  peculiar  character. 


CHROMIC    SALTS.  157 

sent,  and  in  fact  converted  into  the  corresponding  sesqui- 
chloride  of  chromium.  Many  other  organic  substances  may 
be  used  in  place  of  alcohol  in  this  experiment,  such  as  sugar, 
oxalic  acid,  &c.  The  reduction  may  also  be  effected  by  hydrc- 
sulphuric  acid  or  even  by  hydrochloric  acid  alone,  if  added  in 
sufficient  excess ;  in  this  last  case,  sesquichloride  of  chromium 
and  chloride  of  potassium  are  then  formed,  and  part  of  the 
chlorine  escapes  as  gas ;   thus  : 

KO.  2Cr03  +  7HC1  =  KCl  +  Cr^Clg  +  7H0  +  3C1. 

The  oxide  of  chromium  is  precipitated  from  the  green  solution 
by  ammonia,  and  falls  as  a  pale  bluish-green  hydrate.  The 
same  oxide  is  obtained  more  directly,  when  to  a  boiling  solu- 
tion of  bichromate  of  potash  a  hot  solution  of  pentasulphide 
of  potassium  is  added,  the  chromic  acid  then  giving  half  its 
oxygen  to  the  sulphur. 

Ilydrated  chromic  oxide  is  soluble  in  acids,  and  forms  salts. 
It  is  also  dissolved  by  potash  and  soda,  but  not  to  a  great 
extent  by  ammonia.  Its  salts  have  a  sweet  taste,  and  are 
poisonous.  The  oxide  itself  becomes  of  a  greener  colour  when 
dried,  and  loses  water.  A  moderate  heat  affects  its  relations 
to  acids,  the  sulphate  of  the  heated  (or  green)  oxide  not 
forming  a  double  salt,  for  -instance,  with  sulphate  of  potash. 
When  heated  to  redness,  it  glows,  or  undergoes  the  same 
cliange  as  zirconia,  bioxide  of  tin,  and  many  other  hydrated 
oxides  when  made  anhydrous ;  becomes  denser,  assumes  a 
pure  green  colour,  and  ceases  to  be  soluble  in  acids. 

The  salts  of  chromic  oxide  exhibit  two  different  modifica- 
tions, green  and  violet;  some  acids,  e.  g.,  sulphuric  and 
hydrochloric,  produce  both  modifications;  others  only  one. 
Ammonia  produces,  in  solutions  of  the  green  salts,  a  bluish-gray 
precipitate,  but  in  solutions  of  the  violet  salts,  a  greenish-gray 
precipitate,  both  of  which,  however,  yield  green  solutions  w  hen 
dissolved  in  sulphuric  or  hydrochloric  acid  (Regnault) ;  accord- 
ing to  II.  Rose,  hov  ever,  the  precipitate  is  bluish-gray  in  both 


158  CHROMlUxM. 

cases.  The  liquid  above  the  precipitate  has  a  reddish  colour, 
und  contains  a  small  quantity  of  chromic  acid.  Potash  and 
soda  form  similar  precipitates,  which  dissolve  in  excess  of  the 
alkali,  forming  green  solutions  from  which  the  chromic  oxide 
is  precipitated  by  boiling.  The  alkaline  carbonates  form 
greenish  precipitates  (violet  by  cc  ndle-light),  which  dissolve  to 
a  considerable  extent  in  excess  of  the  reagent.  Hydtosulphuric 
acid  forms  no  precipitate  ;  sidphide  of  ammonium  throws  down 
the  hydi'ated  sesquioxide. 

ZinCf  immersed  in  a  solution  of  chrome  alum  or  sesqui- 
chloride  of  chromium  excluded  from  the  air,  gradually  reduces 
the  chromic  salt  to  a  chromous  salt,  the  liquid  after  a  few 
hours  acquiring  a  fine  blue  colour,  and  hydrogen  being  evolved 
by  decomposition  of  water.  If  the  zinc  be  left  in  the  liquid 
after  the  change  of  colour  from  green  to  blue  is  complete, 
hydrogen  continues  to  escape  slowly,  and  the  liquid  after  some 
weeks  or  months,  is  found  no  longer  to  contain  chromium,  the 
whole  of  that  metal  being  precipitated  in  the  form  of  a  basic 
salt,  and  its  place  taken  by  zinc.  Tin,  at  a  boiling  heat,  like- 
wise reduces  the  chromic  salt  to  a  chromous  salt,  but  only  to 
a  limited  extent ;  and  on  lea\ing  the  liquid  to  cool  after  the 
action  has  ceased,  a  contrary  action  takes  place,  the  proto- 
chloridc  of  chromium  decomposing  the  protochloridc  of  tin 
previously  formed,  reducing  the  tin  to  the  metallic  state,  and 
being  itself  reconverted  into  sesquichloride.  Iron  does  not 
reduce  chromic  salts  to  chromous  salts,  but  merely  precipi- 
tates a  basic  sulphate  of  chromic  oxide,  or  an  oxychloride,  as 
the  case  may  be.  * 

Sesquioxide  (and  also  the  protoxide)  of  chromium,  ignited 
with  an  alkaline  carbonate,  or  better  with  a  mixture  of  the 
carbonate  and  nitre,  is  converted  into  chromic  acid,  which 
unites  with  the  alkali  ;  and  en  dissolving  the  fused  product 
in  water,  filtering  if  necessary,  and  neutralising  with  acetic 
acid,  the  characteristic  reactions  of  chromic  acid   (p.  164.) 

•  H.  Loewpl,  Ann.  Ch.  Phya.  [3.1  xl.  42. 


CHROMIC    SALTS.  159 

may  be  obtained  with  lead  and  silver-salts.  An  oxide  of 
chromium  fused  with  borax,  in  either  blowpipe  flame,  yields 
an  emerald-green  glass.  The  same  character  is  exhibited  by 
those  salts  of  chromic  acid  whose  bases  do  not  of  themselves 
impart  decided  colours  to  the  bead. 

A  sesquisulphide  of  chromium,  Cr2S3,  corresponding  with 
the  oxide,  is  obtained  by  exposing  the  latter,  in  a  porcelain 
tube,  to  the  vapour  of  bisulphide  cf  carbon,  at  a  bright  red 
heat.  It  is  a  substance  of  a  dark  grey  colour,  which  is  dissolved 
by  nitric  acid. 

Sesquichloride  of  chromium,  Chromic  chloride,  Cr2Cl3;  160*1 
or  2001*2. — This  salt  is  obtained  as  a  sublimate  of  a  peach- 
purple  colour,  when  chlorine  is  passed  over  a  mixture  of  oxide  of 
chromium  and  charcoal,  ignited  in  a  porcelain  tube  :  or  in  the 
hydrated  state  by  evaporating  the  solution  of  sesquichloride  of 
chromium  to  dryness.  The  salt  obtained  by  the  latter  process 
is  a  green  powder  containing  Cr^Clg  -\-  9H0.  When  heated, 
it  gives  off  water  and  hydrochloric  acid,  and  leaves  a  residue 
of  oxy chloride  of  chromium.  Heated  in  a  current  of  hydro- 
chloric acid  gas,  it  likewise  parts  with  its  water,  and  is  con- 
verted into  the  violet  anhydrous  sesquichloride.  The  solution, 
evaporated  in  vacuo,  leaves  an  amorphous  mass  which  dissolves 
in  water  with  evolution  of  heat,  and  consists  of  Cr2Cl3H-6HO 
(Peligot).  Anhydrous  sesquichloride  of  chromium  is  perfectly 
insoluble  in  cold  water,  and  dissolves  but  very  slowly  in  boiling 
water  ;  but  if  to  cold  water  in  which  the  sesquichloride  is  im- 
mersed, there  be  added  a  very  small  quantity,  even  -ttitu-o,  of 
protochloride  of  chromium,  a  green  solution  is  formed  identical 
Avith  that  which  is  obtained  by  dissolving  chromic  oxide  in 
hydrochloric  acid  (Peligot). 

Chromic  sulphate,  Cr2  03.3S03;  197*6  or  247*0.  —  Chromic 
oxide  is  dissolved  by  sulphuric  acid,  but  the  salt  does  not 
crystallise.  Chromic  sulphate  exhibits  a  violet  and  a  green 
modification.  The  violet  sulphate  is  obtained  by  leaving 
8  parts  of  hydrated  chromic  oxide,  dried  at  212*^,  and  8  or  10 


IGO  '  CHROMIUM. 

parts  of  strong  sulphuric  acid  in  a  loosely  stoppered  bottle  for 
several  weeks.  Tlie  solution,  wliich  is  green  at  first,  gra- 
dually becomes  blue,  and  deposits  a  greenish  blue  crystalline 
mass.  On  dissolving  this  substance  in  water,  and  adding 
alcohol,  a  violet-blue  crystalline  precipitate  is  formed;  and 
by  dissolving  this  precipitate  in  very  weak  alcohol,  and  leav- 
ing the  solution  to  itself  for  some  time,  small  regular  octa- 
hedrons are  deposited,  containing  Cr203.3S03  +  15110. 
The  green  sulphate  is  prepared  by  dissolving  cliromic  oxide  in 
strong  sulphuric  acid  at  a  temperature  between  122°  and 
140°;  also  by  boiling  a  solution  of  the  violet  sulphate.  The 
liquid,  when  quickly  evaporated,  yields  a  green  crystalline 
salt,  having  the  same  composition  as  the  violet  sulphate.  The 
green  sulj  hate  dissolves  readily  in  alcohol,  forming  a  blue 
solution;  but  the  violet  salt  is  insoluble  in  alcohol.  The 
solution  of  the  green  sulphate  is  not  completely  decomposed 
by  soluble  baryta-salts  at  ordinary  temperatures,  a  boiling 
heat  being  required  to  complete  it ;  the  violet  sulphate,  on 
the  contrary,  is  deprived  of  all  its  sulphuric  acid  by  baryta- 
salts  at  ordinary  temperatures.  When  either  the  green  or 
the  violet  sulphate  is  heated  to  390°,  with  excess  of  sulphuric 
acid,  a  light  yellow  mass  is  obtained,  which,  when  further 
heated,  leaves  a  residue  cf  anhydrous  chromic  sulphate,  having 
a  red  colour.  This  anhydrous  salt  is  completely  insoluble  in 
water,  and  dissolves  with  difficulty  even  in  acid  liquids.* 

Chromic  sulphate  forms  a  crystallisable  double  salt  with  sul- 
phate of  potash,  viz.,  chrome-alum,  KO.SO.3-f  Cr203.3S03^- 
21•HO.  Tliis  salt  is  produced  when  a  mixture  of  its  con- 
stituent salts,  with  a  little  free  sulphuric  acid,  is  left  to  spon- 
taneous evaporation.  The  best  mode  of  preparing  it  is  to 
mix  three  parts  of  a  saturated  solution  of  neutral  chromate  of 
potash,  first  with  one  part  of  oil  of  vitriol,  and  then  with  two 
parts  of  alcohol,  which  is  to  be  added  by  small  portions  to  the 

*  Rognault,  Cours  de  Cliimie. 


CHEOME-ALUM.  161 

mixture  of  acid  and  chromatCj  and  not  to  apply  artificial 
heat.  The  chromic  acid  is  thus  deoxidised  in  a  gradual 
manner,  and  large  crystals  of  the  double  sulphate  are  slowly 
deposited  (Fischer).  The  octohedral  crystals  of  chrome-alum 
are  of  a  dark  purple  colour,  and  of  a  beautiful  ruby-red, 
when  so  small  as  to  be  transparent.  The  solution  is  bluish- 
purple,  but  when  heated  to  140°  or  180°  becomes  green,  and, 
according  to  Fischer,  either  deposits  on  evaporation  a  bright- 
green  amorphous,  difficultly  soluble  mass,  or  yields  crystals 
of  sulphate  of  potash,  while  green  chromic  sulphate  remains 
in  solution.  According  to  Loewel*,  on  the  contrary,  the 
change  of  the  purple  into  the  green  salt  does  not  arise  from 
a  separation  of  the  two  simple  salts,  but  merely  from  loss 
of  water  of  crystallisation.  A  solution  of  chrome-alum,  which 
has  become  green  and  uncrystallisable  by  heating,  does  not 
deposit  any  sulphate  of  potash  even  when  concentrated; 
neither  does  that  salt  separate  when  the  crystals  are  melted 
in  a  sealed  tube ;  but  the  green  liquid  obtained  by  either  of 
these  processes  yields,  when  heated  to  77°  and  86°  in  a  dry 
atmosphere,  a  dark  green  mass  containing  Cr203.3S03  -f- 
KO.SO3,  with  scarcely  6  eq.  water  (Loewel).  The  violet 
crystals  containing  24  Aq.,  when  left  for  several  days  in  dry 
air  at  a  temperature  between  11^  and  86°,  give  off  12  Aq., 
and  assume  a  lilac  colour.  At  212°,  another  quantity  of 
water  goes  off,  and  the  crystals  become  green;  and,  by 
gradually  raising  the  temperature  to  about  660°,  the  whole 
of  the  water  may  be  expelled  without  causing  the  salt  to 
melt.  The  anhydrous  crystals  are  green,  and  dissolve  without 
residue  in  boiling  water,  but  at  a  temperature  somewhat 
above  660°,  they  suddenly  become  greenish-yellow,  without 
perceptible  loss  of  weight,  and  are  afterwards  perfectly  in, 
soluble  in  water. 

Oxalate  of  chromium  andpotashjS{KO.C20^)  +  Cr203,3C203 
H-  6H0.  —  This  is  another  beautiful  double  salt  of  chromium. 

*  Ann.  Ch.  Phys.  [3.]  xliv.  313. 
VOL.  IT.  M 


163  CHROMIUM. 

It  is  easily  prepared  by  the  following  process  of  Dr.  Gregory  :  — 
One  part  of  bichromate  of  potash,  two  parts  of  binoxalatc  of 
potash,  and  two  parts  of  crystallised  oxalic  acid  are  dissolved 
together  in  hot  water.  A  copious  evolution  of  carbonic  acid 
gas  takes  place,  arising  from  the  deoxidation  of  the  chromic 
acid,  at  the  expense  of  a  portion  of  the  oxalic  acid;  and 
nothing  fixed  remains,  except  the  salt  in  question,  of  which  a 
pretty  concentrated  solution  crystallises  upon  cooling  in  pris- 
matic crystals,  which  are  black  by  reflected  light,  but  of  a 
splendid  blue  by  transmitted  light,  when  sufficiently  thin  to 
be  translucent.  The  oxide  of  chromium  is  not  completely 
precipitated  from  this  salt  by  an  alkaline  carbonate ;  and  it  is 
remarkable  that  only  a  small  portion  of  the  oxalic  acid  is 
thrown  down  from  it  by  chloride  of  calcium.  When  fully 
dried  and  then  carefully  ignited,  this  salt  is  completely  de- 
composed, and  leaves  a  mixture  of  chromate  and  carbonate  of 
potash.  The  corresponding  double  oxalate  of  chromium  and 
soda  contains  OHO,  according  to  Mitscherlich.  In  the  analo- 
gous oxalate  of  ferric  oxide  and  soda,  the  proportion  of  water 
appeared  to  the  author  to  be  lOHO. 

The  mineral  chrome-iron^  FeO-CrjOg,  crystallises  in  octo- 
hedrons,  and  corresponds  with  the  magnetic  oxide  of  iron, 
having  the  sesquioxide  of  iron  replaced  by  sesquioxide  of 
chromium.  Its  density  is  4*5 ;  it  is  about  as  soft  as  felspar, 
and  infusible.  When  exposed  to  long-continued  calcination, 
in  contact  with  carbonate  of  potash,  in  a  reverberatory  fur- 
nace, the  oxide  of  chromium  of  this  compound  absorbs  oxygen, 
and  combines  as  chromic  acid  with  the  potash,  while  the 
protoxide  of  iron  becomes  sesquioxide.  The  addition  of  nitre 
increases  the  rapidity  of  oxidation,  but  is  not  absolutely 
required  in  the  process.  A  yellow  alkaline  solution  of  car- 
bonate and  chromate  of  potash  is  obtained  by  lixiviating  the 
calcined  matter,  which  is  generally  converted  into  the  red 
chromate  or  bichromate  of  potash,  by  the  addition  of  the 
proper    quantity   of    sulphuric    acid,    the   latter    salt    being 


CHROMIC    ACID.  163 

more  easily  purified  by  crystallisation  than  the  neutral  cliro- 
mate. 

Chromic  acid,  CrOg,  52*19  or  651'8.  —  This  acid  is  not 
liberated  from  the  chromates  in  a  state  of  purity  by  any  acid 
except  the  fluosilicic;  it  is  also  easily  altered.  Fluosilicic 
acid  gas  is  ccmducted  into  a  warm  solution  of  bichromate  of 
potash,  till  the  potash  is  completely  separated  as  the  insoluble 
fluoride  of  silicon  and  potassium,  which  may  be  ascertained 
by  testing  a  few  drops  of  the  solution  with  tartaric  acid  or 
chloride  of  platinum.  The  solution  is  evaporated  to  dryness 
by  a  steam  heat,  and  the  chromic  acid  redissolved  by  water ; 
it  gives  an  opaque,  dull  red  solution.  Chromic  acid  may  also 
be  obtained  anhydrous  and  in  acicular  crystals,  by  distilling, 
in  a  platinum  retort,  a  mixture  of  4  parts  of  chromate  of  lead, 
3  parts  of  finely  pulverised  fluor  spar,  and  7  parts  of  Nord- 
hausen  sulphuric  acid;  sulphate  of  lime  is  formed,  together 
with  perfluoride  of  chromium,  the  vapour  of  which  is  received 
in  a  large  platinum  crucible,  covered  with  wet  paper  and  used 
as  a  condenser.  The  perfluoride  is  decomposed  by  the  aqueous 
vapour  from  the  paper,  being  resolved  into  hydrofluoric  acid 
and  beautiful  orange-red  acicular  crystals  of  chromic  acid, 
which  fill  the  crucible.  A  third  and  easier  method  of  pre- 
paring chromic  acid  is  to  mix  a  solution  of  bichromate  of 
potash,  saturated  between  122°  and  140°,  with  IJ  times  its 
volume  of  strong  sulphuric  acid,  adding  the  acid  by  successive 
small  portions.  Bisulphate  of  potash  is  then  formed,  which 
remains  in  solution,  and  the  liquid,  as  it  cools,  deposits  the 
chromic  acid  in  long  red  needles.  These  may  be  drained, 
first  in  a  funnel,  afterwards  on  a  brick;  then  dissolved  in 
water ;  the  solution  treated  with  a  small  quantity  of  chromate 
of  baryta  to  remove  the  last  portion  of  sulphuric  acid ;  and 
the  filtered  liquid  evaporated  in  vacuo.  Chromic  acid  difters 
remarkably  from  sulphuric  acid,  in  having  but  little  affinity 
for  basic  water,  so  that  it  may  be  obtained  anhydrous  by 
evaporating  its  solution  to  dryness.     Indeed,  the  chromate  of 

M  2 


164  CHROMIUM. 

water  is  not  known  to  exist,  even  in  combination,  both  the 
bichromate  and  terchromate  of  potash  being  anhydrous  salts. 
The  free  acid  is  a  powerful  oxidizing  agent,  and  bleaclies 
organic  colouring  matters :  chromic  acid  then  loses  half  its 
oxygen,  and  becomes  oxide  of  chromium.  It  is  also  con- 
verted into  sesquichloride  of  chromium  by  hydrochloric  acid, 
with  evolution  of  chlorine  : 

2Cr03  +  6HC1  =  Cr2Cl3  -f-  6H0  +  3C1; 

and  into  sesquioxide  by  hydrosulphuric  acid,  with  precipitation 
of  sulphur : 

2Cr03  +  3HS  =  Cr203  +  3110  +  3S. 

Sulphurous  acid  passed  through  a  sclution  of  chromic  acid, 
or  its  salts,  throws  down  a  brown  precipitate,  consisting  of 
monochromate  of  chromic  oxide,  or  bioxide  of  chromium; 
Cr203.Cr03  =  3Cr02.  The  other  intermediate  oxides,  or 
chromates  of  chromic  oxide  mentioned  on  page  153.,  are 
formed  by  other  imperfect  reductions  of  chromic  acid,  or  by 
the  imperfect  oxidation  of  chromic  oxide.  They  are  all  brown 
substances,  soluble  in  potash  and  in  nitric  acid.  One  of 
them,  the  bichromate,  dissolves  also  without  decomposition  in 
hydrochloric  and  sulphuric  acid ;  the  others  are  reduced  by 
hydrochloric  acid  to  sesquichloride,  with  evolution  of  chlorine, 
and  resolved  by  sulphuric  acid  into  chromic  acid  and  sulphate 
of  chromic  oxide.* 

Chromic  acid  forms  bibasic,  monobasic,  biacid,  and  a  few 
tri-acid  salts.  Themonochromates  of  the  alkalies  are  yellow, 
the  bichromates  red ;  the  chromates  of  the  metals  proper  are 
bright  yellow,  red,  or  occasionally  of  some  other  colour.  All 
chromates  heated  with  oil  of  vitriol  give  off  oxygen,  and  form 
sulphate  of  chromic  oxide,  together  with  another  sulphate. 
When  heated  with  hydrochloric  acid,  they  give  ojff  chlorine 

*  For  a  full  account  of  these  brown  oxides,  see  the  translation  of  QmeKn's 
Handbook,  ir.  113. 


CHROMATES.  165 

and  form  sesquichloride  of  chromium,  together  with  another 
metallic  chloride.  Heated  in  the  anhydrous  state  with  com- 
mon salt  and  sulphuric  acid,  they  give  off  red  vapours  of 
chlorochroraic  acid,  which  condense  to  a  brownish  red  liquid. 
Similarly,  when  heated  with  fluor  spar  and  sulphuric  acid,  they 
give  off  red  vapours  of  terfluoride  of  chromium.  A  few  only 
of  the  chromates,  more  particularly  those  of  the  alkalies,  are 
soluble  in  water,  but  they  all  dissolve  in  nitric  acid.  Solu- 
tions of  the  alkaline  chromates  form  a  pale  yellow  precipitate 
wdth  baryta  salts ;  bright  yellow  with  lead-salts ;  brick  red 
with  mercurous  salts ;  and  crimson  with  silver  salts. 

Chromate  of  potash ,  Yellow  chromate  of  potash,  KO.CrOg ; 
97'8  or  1222*5. — This  salt  is  produced  in  the  treatment  of 
the  chrome  ore,  but  is  seldom  crystallised.  It  may  be  formed 
from  the  bichromate,  by  fusing  that  salt  with  an  equivalent 
quantity  of  carbonate  of  potash  ;  or  by  adding  caustic  potash 
to  a  red  solution  of  the  bichromate,  till  its  colour  becomes  a 
pure  golden  yellow.  The  solution  of  chromate  of  potash  has 
a  great  tendency  to  effloresce  upon  the  sides  of  the  basin 
when  evaporated.  Its  crystals  are  of  a  yellow  colour,  anhy- 
drous, and  isomorphous  with  sulphate  of  potash.  One  hundred 
parts  of  water  at  10°  dissolve  48^^  parts  of  this  salt ;  the  solu- 
tion preserves  its  yellow  colour,  even  when  diluted  to  a  great 
degree. 

Bichromate  of  potash.  Red  chromate  of  potash. — K0.2Cr03 ; 
148*6  or  1857*5. — This  beautiful  salt,  of  which  a  large  quan- 
tity is  consumed  in  the  arts,  crystallises  in  prisms  or  in  large 
four-sided  tables,  of  a  fine  orange-red  colour.  It  fuses  below 
a  red  heat,  and  forms  on  cooling  a  crystalline  mass,  the  crys- 
tals of  which  have,  according  to  Mitscherlich,  the  same  form 
as  those  obtained  from  an  aqueous  solution ;  but  this  mass 
falls  to  powder  as  it  cools,  from  the  unequal  contraction  of 
the  crystals  in  different  directions.  At  60°,  water  dissolves 
-rV  of  its  weight  of  this  salt,  and  at  the  boiling  point  a  con- 
siderably greater  quantity. 

M  3 


166  CHROMIUM. 

Bichromate  of  chloride  of  potassium,  Peligofs  salt,  KCl. 
2Cr03. — This  salt,  which  we  are  obliged  to  designate  as  if  it 
contained  chloride  of  potassium  combined  as  a  base  with 
chromic  acid,  is  formed  by  dissohing  together,  with  the  aid 
of  heat,  about  three  parts  of  bichromate  of  potash  and  four  of 
concentrated  hydrochloric  acid,  with  a  small  quantity  of  water, 
avoiding  the  evolution  of  chlorine.  It  ciystallises  in  fiat  red 
quadrangular  prisms,  and  is  decomposed  by  solution  in  pure 
water. 

Terchromate  of  potash,  KO.SCrOg,  is  obtained  crj^stallised 
when  a  solution  of  the  bichromate  is  mixed  with  nitric  acid, 
and  evaporated.  Bichromates  of  soda  and  silver  exist  which 
are  anhydrous,  like  the  bichromate  of  potash  (Warington). 

Chromate  of  soda,  NaO-CrOg  +  lOHO.— By  the  evapora- 
tion of  a  concentrated  solution  of  this  salt,  it  is  obtained  in 
large  fine  crystals,  having  the  form  of  glaubcr  salt.  The 
bichromate  crystallises  in  thin,  hyacinth-red,  six-sided  prisms, 
bevelled  at  the  ends. 

Chromate  of  ammonia,  NH40.Cr03  is  prepared  by  evapora- 
ting a  mixture  of  chromic  acid  with  a  slight  excess  of  ammo- 
nia. It  crystallises  in  lemon-yellow  needles,  very  soluble  in 
water,  and  having  an  alkaline  reaction  and  pungent  saline 
taste.  When  heated,  they  give  off  ammonia,  water,  and 
oxygen,  and  leave  sesquioxide  of  chromium.  The  bichromate, 
NH40.2Cr03,  forms  orange-yellow  or  reddish  bro^vn  rhombic 
tables,  which  at  a  heat  below  redness  are  decomposed,  with 
emission  of  light  and  feeble  detonation,  leaving  the  sesqui- 
oxide. It  combines  with  chloride  of  mercury,  forming  crys- 
talline compounds,  containing  NH40.2Cr03.HgCl  +  HO,  and 
3(NH40.2Cr03).HgCl  (Richmond  and  Abel).*  Rammelsberg 
has  obtained  an  acid  salt  composed  of  NH4O.6CrO3  +  10HO. 

Chromate  of  baryta,  BaO.CrOg  is  a  lemon-yellow  powder 
obtainedby  precipitating  a  baryta-salt  with  an  alkaline  chromate. 

*  Chem.  Soc.  Qu.  J.  iii  139. 


CHROMATES.  167 

It  is  insoluble  in  water,  but  dissolves  easily  in  nitric,  hydro- 
chloric, or  chromic  acid.  When  a  baryta-salt  is  precipitated  with 
neutral  chromate  of  potash,  and  sulphuric  acid  added,  the  pre- 
cipitate dissolves  with  partial  decomposition,  and  on  diluting 
with  water,  mixing  the  filtered  solution  with  chromic  acid, 
and  evaporating  in  vacuo,  neutral  chromate  of  baryta  first 
separates,  then  crystals  of  a  bichromate,  Ba0.2Cr03  +  2HO, 
and  afterwards  a  double  salt  containing  2(Ba0.3Cr03.HO)  + 
(KO.3CrO3.HO).     (Bahr.)* 

Neutral  chromate  of  lime,  CaO.Cr03,  is  obtained  by 
treating  carbonate  of  lime  with  aqueous  chromic  acid ;  and 
by  treating  the  neutral  salt  with  excess  of  chromic  acid  and 
evaporating,  a  bichromate,  Cr0.2Cr03  +  2H0,  is  obtained. 
Chloride  of  calcium  mixed  with  monochromate  of  potash,  yields 
a  double  salt  containing  5(CaO.Cr03)  +  KO.CrOg.     (Bahr.) 

Chromate  of  magnesia  forms,  according  to  the  author's  ob- 
servations, yellow  crystals  which  are  very  soluble,  and  contain 
5 HO.  It  does  not  form  a  double  salt  with  chromate  of 
potash,  as  sulphate  of  magnesia  does  with  sulphate  of  potash. 
It  is  remarked  that  the  insoluble  metallic  chromates  generally 
carry  down  portions  of  the  neutral  precipitating  salts,  or  of 
subsalts,  and  their  analysis  is  often  unsatisfactory  from  that 
cause.  When  the  magnesian  chromates  are  compared  with 
the  sulphates  of  the  same  family,  the  former  are  found  to 
have  their  water  readily  replaced  by  metallic  oxides,  but  not 
by  salts;  so  that  subchromates  with  excess  of  oxide  are 
numerous,  while  few  or  no  double  chromates  exist. 

Chromate  of  lead,  PbO.CrOg ;  162*4  or  2030.— This  com- 
pound, so  well  known  as  chrome-yellow,  is  obtained  by  mixing 
nitrate  or  acetate  of  lead  with  chromate  or  bichromate  of 
potash.  The  precipitate  is  of  a  lighter  shade  from  dilute  than 
from  concentrated  solutions.  It  is  entirely  soluble  in  potash 
or  soda,  but  not  in  dilate  acids. 

Subchromate  of  lead,  2PbO.Cr03,  is  of  a  red  colour.     It  is 

*  J.  pr.  Chem.  Ix.  60. 
If  4k 


168  •  CHROMIUM. 

formed  when  a  solution  of  neutral  chromate  of  potash^  mixed 
with  as  much  free  alkali  as  it  already  contains,  is  added  to  a 
solution  of  nitrate  of  lead.  But  the  finest  vermilion-red 
subchromate  is  formed  when  one  part  of  the  neutral  chromate 
of  lead  is  thrown  into  five  parts  of  nitre  in  a  state  of  fusion  by 
heat.  Water  dissolves  the  chromate  and  nitrate  of  potash  in 
the  fused  mass,  and  leaves  the  subchromate  of  lead  as  a  crys- 
talline powder,  (Liebig  and  Wohler).  An  orange  pigment 
may  be  obtained  very  economically,  by  boiling  the  sulphate 
of  lead,  which  is  a  waste  product  in  making  acetate  of  alumina 
from  alum  by  means  of  acetate  of  lead,  with  a  solution  of 
chromate  of  potash.  The  subchromate  of  lead  forms  a  beau- 
tiful orange  upon  cloth,  which  is  even  more  stable  than  the 
yellow  chromate,  not  being  acted  upon  by  cither  alkalies  or 
acids.  One  method  of  dyeing  chrome-orange,  is  to  fix  the 
yellow  chromate  of  lead  first  in  the  calico,  by  dipping  it  suc- 
cessively in  acetate  of  lead  and  bichromate  of  potash,  and  then 
washing  it.  This  should  be  repeated,  in  order  to  precipitate 
a  considerable  quantity  of  the  chromate  in  the  calico.  A  milk 
of  lime  is  then  heated  in  an  open  pan ;  and  when  it  is  at  the 
point  of  ebullition,  the  yellow  calico  is  immersed  in  it,  and 
instantly  becomes  orange,  being  deprived  of  a  portion  of  its 
chromic  acid  by  the  lime,  which  forms  a  soluble  chromate 
of  lime.  At  a  lower  temperature,  lime-water  dissolves  the 
chromate  of  lead  entirely,  and  leaves  the  cloth  white. 

Chromate  of  silver  falls  as  a  reddish  brown  precipitate  when 
nitrate  of  silver  is  added  to  neutral  chromate  of  potash.  Dis- 
solved in  hot  and  concentrated  solution  of  ammonia,  it  yields, 
on  cooling,  large  well  formed  crystals,  AgO  CrOg  +  2NH3, 
isomorphous  with  the  analogous  ammoniacal  sulphate  and 
seleniate  of  silver. 

Chlorochromic  acid,  CrOgCl,  or  2Cr03.CrCl3. — This  is  a 
volatile  liquid,  obtained  by  distilling,  in  a  glass  retort,  at  a 
gentle  heat,  3  parts  of  bichromate  of  potash  and  3  J  parts  of 
common    salt,    previously    reduced    to   powder    and    mixed 


ESTIMATION    OF    CHROMIUM.  169 

together,  with  5  parts  by  water-measure  of  oil  of  vitriol, 
discontinuing  the  distillation  when  the  vapours,  from  being  of 
a  deep  orange-red,  become  pale — that  change  arising  from 
watery  vapour.  The  compound  is  a  heavy  red  liquid,  decom- 
posed by  water.     The  density  of  its  vapour  is  5*9. 

Terfluoride  of  chromium,  CvY^,  is  obtained  in  the  manner 
already  mentioned  under  the  preparation  of  chromic  acid.  It 
is  a  blood-red  liquid.  No  corresponding  terchloride  of  chro- 
mium has  been  obtained  in  an  isolated  state. 

Per  chromic  acid,  CrgO^.  —  When  peroxide  of  hydrogen 
dissolved  in  water  is  mixed  with  a  solution  of  chromic  acid, 
the  liquid  assumes  a  deep  indigo-blue  colour,  but  often  loses 
this  colour  very  rapidly,  giving  off  oxygen  at  the  same  time. 
The  same  blue  colour  is  formed  by  adding  a  mixture  of 
aqueous  peroxide  of  hydrogen  and  sulphuric  or  hydrochloric 
acid  to  bichromate  of  potash;  but,  in  a  very  short  time, 
oxygen  is  evolved,  and  a  potash-salt,  together  with  a  chromic 
salt,  left  in  solution.  For  each  atom  of  K0.2Cr03,  four 
atoms  of  oxygen  are  evolved,  provided  an  excess  of  HOg  be 
present : 
K0.2Cr03  +  O  +  4SO3  =  KO.SO3  +  Cr203.3S03  +  40. 

The  peroxide  of  hydrogen  first  gives  up  1  at.  O  to  the  2  at.  of 
Cr03,  and  forms  Crfiyj ;  and  this  compound  is  subsequently 
resolved  into  Cr203  and  40.  With  ether,  perchromic  acid 
forms  a  more  stable  blue  mixture  than  with  water,  and  in 
this  state  may  be  made  to  unite  with  ammonia  and  with 
certain  organic  bases,  forming  very  stable  compounds,  from 
which  stronger  acids  separate  the  blue  acid. 


ESTIMATION    OF  CHROMIUM,   AND  METHODS  OF  SEPARATING   IT 
FROM    THE    PRECEDING    METALS. 

Chromium  is  usually  estimated  in  the  state  of  sesquioxide. 
When  it  exists  in  solution  in  that  state,  it  may  be  precipitated 


170  CHROMIUM. 

by  ammonia,  care  being  taken  to  avoid  a  large  excess  of  that 
reagent  (which  would  dissolve  a  portion),  and  to  heat  the 
liquid  for  some  time.  The  chromic  oxide  is  then  completely 
precipitated,  and  the  precipitate,  after  washing  and  drying,  is 
reduced  by  ignition  to  the  state  of  anhydrous  sesquioxide,  con- 
taining 70-1  per  cent,  of  the  metal. 

When  chromium  exists  in  solution  in  the  state  of  chromic 
acid,  it  is  best  to  precipitate  it  by  a  solution  of  mercurous 
nitrate ;  the  mercurous  chromate  thereby  thrown  down  yields 
by  ignition  the  anhydrous  sesquioxide.  The  chromic  acid 
might  also  be  precipitated  and  estimated  in  the  form  of  a 
baryta  or  lead  salt. 

Chromic  acid  may  also  be  estimated  by  means  of  oxalic 
acid,  which  reduces  it  to  sesquioxide,  being  itself  converted 
into  carbonic  acid.  The  quantity  of  carbonic  acid  evolved 
determines  the  quantity  of  chromic  acid  present,  3  eq.  CO2 
corresponding  to  1  eq.  CrOg,  as  shown  by  the  equation : 

2Cr03  +  3C2O3  =  Cr203  +  GCO2. 

The  mode  of  proceeding  is  the  same  as  that  adopted  for  the 
valuation  of  black  oxide  of  manganese  (p.  17).  If  the  object 
be  merely  to  determine  the  quantity  of  chromium  present,  any 
salt  of  oxalic  acid  may  be  used ;  but  if  the  alkalies  are  also  to 
be  estimated  in  the  remaining  liquid,  the  ammonia  or  baryta 
salt  must  be  used. 

Chromic  oxide,  in  the  state  of  neutral  or  acid  solution,  is 
easily  separated  from  the  alkalies  or  alkaline  earths,  by  pre- 
cipitation with  ammonia,  care  being  taken  in  the  latter  case 
to  protect  the  liquid  and  precipitate  from  the  air.  The  same 
method,  with  addition  of  sal-ammoniac,  serves  to  separate 
chromic  oxide  from  magnesia.  The  separation  from  the 
alkaline  earths  and  from  magnesia  may  also  be  effected  by 
precipitating  the  whole  with  an  alkaline  carbonate,  and  igniting 
the  precipitate  with  a  mixture  of  carbonate  of  soda  and  nitre. 
The  chromium  is  then  converted  into  chromate  of  soda,  which 


ESTIMATION    OF    CHROMIUM.  171 

may  be  dissolved  out,  and  the  solution,  after  neutralisation 
with  nitric  or  acetic  acid,  treated  with  mercurous  nitrate  as 
above. 

From  alumina  and  glucina,  chromic  oxide  may  be  separated 
by  treating  the  solution  with  excess  of  potash,  and  boiling 
the  liquid  to  precipitate  the  chromic  oxide.  The  separation 
is,  however,  more  completely  effected  by  fusing  with  nitre 
and  carbonate  of  soda,  treating  the  fused  mass  with  water, 
adding  an  excess  of  nitric  acid  to  dissolve  anything  that  may 
be  insoluble  in  water,  and  precipitating  the  alumina  or  glucina 
by  ammonia. 

Another  method  of  converting  chromic  oxide  into  chromic 
acid,  and  thereby  effecting  its  separation  from  the  above- 
mentioned  oxides,  is  to  treat  the  mixture  with  excess  of 
potash,  and  heat  the  solution  gently  with  bioxide  of  lead. 
The  whole  of  the  chromium  is  then  converted  into  chromic 
acid,  and  remains  dissolved  as  chromate  of  lead  in  the  alkaline 
liquid ;  and  on  filtering  from  the  excess  of  bioxide  of  lead, 
and  any  other  insoluble  matter  that  may  be  present,  and 
supersaturating  the  filtrate  with  acetic  acid,  the  chromate  of 
lead  is  precipitated  (Chancel).* 

Chromic  acid  may  be  separated  from  the  alkalies  in  neutral 
solutions  by  precipitation  with  mercurous  nitrate;  also  by 
reducing  it  to  chromic  oxide  with  hydrochloric  acid  and 
alcohol,  and  precipitating  by  ammonia.  From  the  earths  it 
may  also  be  separated  by  this  latter  method,  or,  again,  by 
fusing  with  carbonate  of  soda,  dissolving  out  with  water,  &c. 

From  manganese,  iron  (in  the  state  of  protoxide),  cobalt, 
nickel,  and  zinc,  chromium  in  the  state  of  sesquioxide  may 
be  separated  by  agitation  with  carbonate  of  baryta,  which 
precipitates  the  chromic  oxide,  leaving  the  protoxides  in 
solution.  The  precipitate  is  then  treated  with  dilute  sulphuric 
acid,  which  dissolves  the  chromic  oxide  and  leaves  the  baryta, 

*  Compt.  rend,  xliii.  927. 


172  •         VANADIUM. 

and  the  filtrate  treated  with  ammonia  to  precipitate  the 
chromic  oxide.  Chromium  may  also  be  separated  from  all 
these  metals,  except  manganese,  by  fusion  with  nitre  and 
carbonate  of  soda,  or  with  the  carbonate  alone  if  it  is  already 
in  the  form  of  chromic  acid.  Or,  again,  the  separation  may 
be  effected  by  means  of  potash  and  bioxide  of  lead,  according 
to  ChancePs  method  above  described. 

From  cadmium,  copper ,  lead,  and  tin,  chromium  is  easily 
separated  by  hydrosulphuric  acid. 

When  sesquioxide  of  chromium  and  chromic  acid  occur 
together  in  a  solution,  the  chromic  acid  may  be  precipitated 
by  mercurous  nitrate,  the  solution  being  first  completely 
neutralised,  and  the  sesquioxide  precipitated  from  the  filtrate 
by  ammonia,  which  at  the  same  time  throws  down  a  mercury- 
compound,  to  be  afterwards  separated  from  the  chromic  acid 
by  ignition. 


SECTION     IV. 

VANADIUM. 

Eg.  68-55  or  856-9;  V. 

Vanadium,  so  named  from  Vanadis,  a  Scandinavian  deity, 
was  discovered  by  Sefstroem  in  1830,  in  the  iron  prepared 
from  the  iron  ore  of  Taberg,  in  Sweden,  and  procured  after- 
wards in  larger  quantity  from  the  slag  of  that  ore.  It  was 
found  afterwards  by  Mr.  Johnston,  in  a  new  mineral  dis- 
covered by  him,  the  vanadiate  of  lead,  from  Wanlockhead.  It 
is  one  of  the  rarest  of  the  elements.  The  metal  itself  has 
considerable  resemblance  in  properties  to  chromium.  It 
combines  with  oxygen  in  three  proportions,  forming  the 
protoxide  of  vanadium,  VO,  bioxide,  VO2,  and  vanadic  acid, 

VO3. 


OXIDES    OF   VANADIUM.  173 

Protoxide  of  vanadium,  VO,  76*55  or  956*9,  is  produced 
by  the  action  of  charcoal  or  hydrogen  upon  vanadic  acid.  It 
is  a  black  powder  of  semi-metallic  lustre,  and  when  made 
coherent  by  pressure,  conducts  electricity  like  a  metal.  It 
does  not  combine  with  acids,  and  exhibits  none  of  the  cha- 
racters of  an  alkaline  base.  It  is  readily  oxidised  when 
heated  in  the  open  air,  and  passes  into  the  following  com- 
pound. 

Bioocide  of  vanadium,  Vanadic  oxide,  VOg,  84*55  or  1056*9, 
is  produced  by  the  action  of  hydrosulphuric  acid  and  other 
deoxidating  substances  upon  vanadic  acid.  When  pure,  it  is 
a  black  pulverulent  substance,  quite  free  from  any  acid  or 
alkaline  reaction.  It  dissolves  in  acids,  and  forms  salts,  most 
of  which  are  of  a  blue  colour.  Vanadic  salts  form,  with  the 
hydrates  and  monocarbonates  of  the  fixed  alkalies,  a  greyish- 
white  precipitate  of  hydrated  vanadic  oxide,  which  dissolves 
in  a  moderate  excess  of  the  reagent,  but  is  precipitated  by  a 
large  excess  in  the  form  of  a  vanadite  of  the  alkali.  Ammonia 
in  excess  produces  a  brown  precipitate,  soluble  in  pure  water, 
but  insoluble  in  water  containing  ammonia.  Ferrocyanide 
of  potassium  forms  a  yellow  precipitate,  which  turns  green  on 
exposure  to  the  air.  Hydrosulphuric  acid  produces  no  pre- 
cipitate. Sulphide  of  ammonium  forms  a  black-brown  pre- 
cipitate, soluble  in  excess.  Tincture  of  galls  forms  a  finely- 
divided  black  precipitate,  which  gives  to  the  liquid  the 
appearance  of  ink. 

Bioxide  of  vanadium  is  also  capable  of  acting  as  an  acid, 
and  forms  compounds  with  alkaline  bases,  some  of  which  are 
crystallisable.  It  is  hence  called  vanadous  acid,  and  its  salts 
vanadites.  These  salts  in  the  dry  state  are  brown  or  black ; 
they  are  all  insoluble  in  water,  excepting  those  of  the  alkalies. 
The  solutions  of  the  alkaline  vanadites  are  brown,  but  when 
treated  with  hydrosulphuric  acid,  they  acquire  a  splendid  red- 
purple  colour,  arising  from  the  formation  of  a  sulphur-salt. 
Acids  colour  them  blue,  by  forming  a  double  salt  of  vanadic 


174  VANADIUM. 

oxide  and  the  alkali.  Tincture  of  galls  colours  them  blackish- 
blue.  The  insoluble  vanadites,  when  moistened  or  covered 
with  water,  become  green,  and  are  converted  into  salts  of 
vanadic  acid. 

Vanadic  acid,  VO3;  92-55  or  1156-9.  —  It  is  in  this  state 
that  vanadium  occurs  in  the  slag  of  the  iron-ore  of  Taberg, 
and  in  the  vanadiate  of  lead.  It  is  obtained  by  dissolving  the 
latter  mineral  in  nitric  acid,  and  precipitating  the  lead  and 
arsenic,  with  which  the  vanadium  is  accompanied,  by  hydro- 
sulphuric  acid.  A  blue  solution  of  bioxide  of  vanadium 
remains,  which  becomes  vanadic  acid  when  evaporated  to 
dryness.  Vanadic  acid  fuses  but  retains  its  oxygen  at  a 
strong  red  heat.  It  is  very  sparingly  soluble,  water  taking  up 
only  l-lOOth  of  its  weight  of  this  compound,  thereby  acquiring 
a  yellow  colour  and  an  acid  reaction.  It  acts  the  part  of  a 
base  to  stronger  acids.  An  interesting  double  phosphate  of 
silica  and  vanadic  acid  was  observed  in  crystalline  scales,  of 
which  the  formula  is  2Si03.P05  +  2VO3.PO5  +  6H0.  Vanadic 
acid  forms,  with  bases,  neutral  and  acid  salts,  the  first  of 
which  admit  of  an  isomeric  modification,  being  both  white 
and  yellow,  while  the  acid  salts  are  of  a  fine  orange-red. 
Vanadic  and  chromic  acids  are  the  only  acids  of  which  the 
solution  is  red,  while  they  are  distinguished  from  each  other 
by  the  vanadic  acid  becoming  blue,  and  the  chromic  acid 
green,  when  they  are  deoxidised.  All  the  vanadiates  are, 
more  or  less  soluble  in  water;  some  of  them,  however,  as 
the  baryta  and  lead  salts,  are  very  sparingly  soluble.  The 
vanadiates  of  the  alkalies  are  sparingly  soluble  in  cold  water, 
especially  if  it  contains  a  free  alkali  or  another  alkaline  salt ; 
e.  g.j  vanadiate  of  ammonia  is  nearly  insoluble  in  water  con- 
taining sal-ammoniac;  hence  on  treating  a  solution  of  vana- 
diate of  potash  with  excess  of  sal-ammoniac,  a  precipitate  of 
vanadiate  of  ammonia  is  produced.  The  aqueous  solutions  of 
the  vanadiates  are  coloured  red  by  the  stronger  acids,  but  the 
mixture  often  becomes  colourless  again  after  a  while.     They 


ESTIMATION    OF   VANADIUM.  175 

give  orange-red  precipitates  with  the  salts  of  teroxide  of 
antimony,  protoxide  of  lead,  protoxide  of  copper,  and  prot- 
oxide of  mercury.  Hydrosulphuric  acid  produces  in  neutral 
solutions  of  the  vanadiates  a  mixed  precipitate  of  sulphur  and 
hydrated  vanadic  oxide ;  in  acid  solutions,  it  merely  throws 
down  sulphur  and  reduces  the  vanadic  acid  to  vanadic  oxide. 
Sulphide  of  ammonium  imparts  to  solutions  of  the  vanadiates 
a  brown-red  colour,  and,  on  adding  an  acid  to  the  solution,  a 
light  brown  precipitate  is  formed,  consisting  of  vanadic  sul- 
phide mixed  with  sulphur;  the  liquid  at  the  same  time 
generally  acquires  a  blue  colour. 

All  compounds  of  vanadium  heated  with  borax  or  phos^ 
p)horus  salt  in  the  outer  blowpipe  flame,  produce  a  clear 
bead,  which  is  colourless  if  the  quantity  of  vanadium  be 
small,  yellow  if  it  be  large;  in  the  inner  flame,  the  bead 
acquires  a  beautiful  green  colour. 

Sulphides  and  chlorides  of  vanadium,  corresponding  with 
the  bioxide  and  vanadic  acid  have  likewise  been  formed.* 


ESTIMATION  OF   VANADIUM,    AND    METHODS  OF  SEPARATING  IT 
FROM    THE     PRECEDING     METALS. 

Vanadium,  in  the  state  of  vanadic  oxide  or  vanadic  acid,  is 
estimated  by  reducing  it  to  the  state  of  protoxide  by  ignition 
in  a  stream  of  hydrogen ;  100  parts  of  the  protoxide  contain 
90-54  of  the  metal. 

In  solutions  of  vanadous  salts,  the  vanadium  is  precipitated 
by  mixing  the  solution  with  excess  of  mercuric  chloride  (cor- 
rosive sublimate),  and  then  with  ammonia.  The  precipitate, 
consisting  of  mercuric  vanadiate,  and  amido- chloride  of  mer- 
cury, is  ignited,  whereupon  vanadic  acid  remains  mixed  only 
with  a  small  quantity  of  mercuric  oxide,  from  which  it  is 
separated  by  solution  in  carbonate  of  ammonia. 

*  Berzeliua,  Ann.  Cli.  Pliys.  [2.]  xlvii.  337. 


176  TUNGSTEN. 

When  vanadic  acid  is  dissolved  in  a  liquid,  it  may  be  ob- 
tained by  evaporating  the  liquid,  and  if  volatile  acids  or 
ammonia  are  also  present,  by  igniting  the  residue. 

Vanadic  acid  may  be  separated  from  many  acids  and  other 
substances,  by  causing  it  to  unite  with  ammonia,  expelling 
the  excess  of  ammonia  by  evaporation,  and  then  adding  a 
saturated  solution  of  sal-ammoniac,  in  which  vanadiate  of 
ammonia  is  insoluble.  The  precipitate  is  then  washed  on  a 
filter,  first  with  solution  of  sal-ammoniac,  then  with  alcohol, 
and  the  ammonia  driven  ofi*  by  ignition.  This  method  serves 
to  separate  vanadic  acid  from  the  fixed  alkalies. 

Vanadium  may  be  separated  from  many  of  the  preceding 
metals  by  the  solubility  of  its  sulphide  in  sulphide  of  ammo- 
nium ;  and  from  others,  which  are  precipitated  from  their  acid 
solutions  by  hydrosulphuric  acid,  by  acidulating  the  liquid, 
and  passing  hydrosulphuric  acid  gas  through  it ;  the  vanadium 
then  remains  dissolved  in  the  form  of  vanadic  oxide. 

From  leadf  baryta,  and  strontia,  vanadic  acid  may  be 
separated  by  fusion  mth  bisulphate  of  potash ;  on  treating 
the  fused  mass  with  water,  sulphate  of  lead,  baryta,  or  stron- 
tia remains,  while  vanadiate  of  potash  is  dissolved.  Sulphuric 
acid  cannot  be  used  to  effect  this  separation,  because  the  pre- 
cipitated sulphate  always  carries  down  with  it  a  portion  of  the 
vanadium. 


SECTION    V. 

TUNGSTEN. 

Syn.  WOLFRAM.     Eq.  94*64,  or  1183  ;  W. 

This  element  exists  in  the  form  of  tungstic  acid  in  several 
minerals,  the  most  important  of  which  are  the  native  tungstate 
of  lime  CaO.WOg,  and  wolfram,  or  the  tungstate  of  manganese 
and   iron,    MnO.WOg  H-3(FeO.W03).      Its  name   tungsten 


TUNGSTEN".  177 

ineatis  in  Swedisii_,  heavy  stone,  and  is  expressive  of  the  great 
density  of  its  compounds. 

Tungstic  acid  parts  with  oxygen  easily,  and  may  be  reduced 
in  a  glass  tube,  by  means  of  dry  hydrogen  gas,  at  a  red  heat. 
The  metal  is  thus  obtained  in  the  state  of  a  dense,  dark  grey 
powder,  which  it  is  necessary  to  expose  to  a  very  violent  heat 
to  fuse  into  globules,  for  tungsten  is  even  less  fusible  than 
manganese.  The  metal,  when  fused,  has  the  colour  and 
lustre  of  iron,  and  is  not  altered  in  air :  it  is  one  of  the 
densest  of  the  metals,  its  specific  gravity  being  from  17*22 
to  17*6.  By  passing  the  vapour  of  chloride  or  oxy chloride  of 
tungsten  mixed  with  hydrogen,  through  a  red-hot  glass  tube, 
the  metal  is  obtained  in  the  form  of  a  dense  specular  film  of 
steel-grey  colour,  and  sp.  gr.  16-54  (Wohler).  When  heated 
to  redness  in  the  pulverulent  form,  it  takes  fire,  burns,  and 
is  converted  into  tungstic  acid.  Tungsten  forms  two  com- 
pounds with  oxygen,  viz.,  tungstic  oxide,  WO2,  and  tungstic 
acid,  WO3. 

Tungstic  oxide,  WO2,  110-64  or  1383.— This  oxide  is  ob- 
tained as  a  brown  powder  when  tungstic  acid  is  reduced  by 
hydrogen  at  a  temperature  not  exceeding  low  redness.  Tung- 
stic acid  may  also  be  deprived  of  oxygen  in  the  humid  way,  by 
pouring  diluted  hydrochloric  acid  over  it,  and  placing  zinc  in 
the  liquor;  the  tungstic  acid  then  gradually  changes  into 
tungstic  oxide,  in  the  form  of  brilliant  crystalline  plates  of  a 
copper-red  colour.  No  saline  compounds  of  this  oxide  with 
acids  are  known.  When  digested  in  a  strong  solution  of 
hydrate  of  potash,  it  dissolves,  with  disengagement  of  hydrogen 
gas  and  formation  of  tungstate  of  potash. 

A  compound  of  tungstic  oxide  and  soda,  Na0.2W02,  of  a 
very  singular  nature,  was  discovered  by  Wohler.  It  is  obtained 
by  adding  to  fused  tungstate  of  soda  as  much  tungstic  acid  as 
it  will  take  up,  and  exposing  the  mass  at  a  red  heat  to 
hydrogen  gas.  After  dissolving  out  the  neutral  undecomposed 
tungstate  by  water,  the  new  compound  remains  in  golden 

VOL.  II.  N 


178  TUNGSTEN. 

yellow  scales  and  regular  cubes,  possessing  tlie  metallic  lustre 
of,  and  a  striking  resemblance  to  gold.  This  compound  is  not 
decomposed  by  aqua  rcgia,  sulphuric  or  nitric  acid,  or  by 
alkaline  solutions,  but  yields  to  hydrofluoric  acid.  It  cannot 
be  prepared  by  uniting  soda  directly  Avith  tungstic  oxide. 

Tungsttc  acid,  WO3 ;  118'G1<  or  1483,  is  most  conveniently 
obtained  by  decomposing  the*native  tungstate  of  lime,  finely 
pulverised,  by  hydrochloric  acid ;  chloride  of  calcium  is  dis- 
solved, and  tungstic  acid  precipitates.  It  is  also  obtained  from 
wolfram  by  digesting  that  mineral  in  nitro-hydrochloric  acid, 
which  dissolves  the  oxides  of  iron  and  manganese,  and  leaves 
the  tungstic  acid  in  the  form  of  a  yellow  powder — or  by  fusing 
the  mineral  ^-ith  four  times  its  weight  of  nitre ;  treating  the 
fused  mass  with  water  to  dissolve  out  the  tungstate  of  potash 
thereby  produced ;  adding  chloride  of  calcium  to  the  filtrate 
to  throw  down  the  tungstic  acid  as  tungstate  of  lime;  and 
decomposing  the  washed  lime-salt  with  nitric  acid.  Dissolved 
in  ammonia  and  reprecipitated  by  acids,  tungstic  acid  always 
forms  a  compound  with  the  acid  employed.  It  may  be  ob- 
tained in  the  separate  state  by  heating  the  tungstate  of 
ammonia  to  redness.  It  is  an  orange-yellow  powder,  which 
becomes  didl  green  when  strongly  heated.  Its  density  is  6*12. 
It  is  quite  insoluble  in  water  and  in  acids,  but  dissolves  in 
alkaline  solutions. 

Tungstic  acid  forms  both  neutral  and  acid  salts  with  the 
alkalies.  Neutral  tungstate  of  potash  KO.WO3  is  a  very 
soluble  salt,  which  may  be  obtained  in  small  crystals  by 
evaporating  its  solution.  When  a  little  acid  is  added  to 
the  solution,  an  acid  salt  precipitates,  which  is  very  slightly 
soluble  in  water.  The  neutral  tungstate  of  soda  is  also  very 
soluble,  but  may  be  obtained  in  good  crystals,  which  contain 
a  large  quantity  of  water  of  crystallisation.  The  acid  tung- 
state of  soda  Na0.2\V03  is  very  crystallisable,  and  soluble  in 
eight  parts  of  water.  A  combination  of  tungstic  acid  with 
tungstic  oxide,  WO2.WO3,  is  obtained  as  a  fine  blue  powder 
when   tungstate    of  ammonia    is    heated    to    redness   in   a 


TUNGSTIC    ACID.  179 

retort,  and  is  also  produced  under  other  circumstances. 
Malaguti  is  disposed  to  consider  this  compound  as  a  distinct 
acid  of  tungsten,  W2O5.  * 

All  the  salts  of  tungstic  acid  have  a  very  high  specific  gra- 
vity.  The  alkaline  and  earthy  tungstates  are  colourless.  The 
only  soluble  tungstates  are  those  of  the  alkalies  and  magnesia. 
Solutions  of  the  alkaline  tungstates  give,  with  hydrochloric, 
nitric,  sulphuric,  and  phosphoric  acid,  white  precipitates  con- 
sisting of  compounds  of  tungstic  acid  with  the  other  acid.  The 
precipitate  formed  by  phosphoric  acid  dissolves  in  excess  of 
that  reagent ;  the  precipitates  formed  by  the  other  three  acids 
turn  yellow  on  boiling.  A  solution  of  an  alkaline  tungstate 
supersaturated  with  sulphuric,  hydrochloric,  phosphoric,  oxalic, 
or  acetic  acid,  yields,  on  the  introduction  of  a  piece  of  zinc, 
a  beautiful  blue  colour  arising  from  the  formation  of  bljie  oxide 
of  tungsten ;  this  effect  is  not  produced  with  nitric,  tartaric,  or 
citric  acid.  Solutions  of  alkaline  tungstates  form  with  lime- 
water  and  with  salts  of  baryta,  lime,  zinc,  lead,  mercury,  and 
silver,  white  precipitates  consisting  of  tungstates  of  those 
bases.  A  soluble  tungstate  mixed  with  sulphide  of  ammonium 
and  then  with  an  acid  in  excess,  yields  a  light  brown  precipi* 
tate  of  sulphide  of  tungsten,  soluble  in  sulphide  of  ammonium. 

With  borax  and  phosphorus-salt  in  the  outer  blow-pipe 
flame,  tungstic  acid  forms  a  colourless  bead;  in  the  inner  flame 
it  forms  with  borax,  a  yellow  glass,  if  the  quantity  of  tung- 
sten present  be  somewhat  considerable,  but  colourless  with  a 
smaller  quantity.  With  phosphorus- salt  in  the  inner  flame  it 
forms  a  glass  of  a  pure  blue  colour,  unless  iron  is  also  present, 
in  which  case  the  colour  is  blood-red;  the  addition  of  tin, 
however,  renders  it  blue. 

The  above  mentioned  characters  of  tungstic  acid,  though 
general,  are  not  invariable.  Tungstic  acid  appears  to  be  sus- 
ceptible of  certain  modifications  analogous  to  those  of  phos- 
phoric acid,  and  depending  upon  the  proportions  in  which  it 

*  Ann.  Ch.  Phys.  [2],  Ix.  271. 
N  2 


180  TUNOSTEN. 

unites  with  water  and  other  bases.  In  some  of  these  modifi- 
cations it  is  much  more  soluble  than  in  others^  and  is  not 
precipitated  by  nitric  or  hydrochloric  acid. 

Laurent  distinguished  five  or  six  classes  of  tungstates,  viz., 
1.  Ordinary  tungstates,  WO3MO,  with  or  without  water  (M 
denoting  a  metal  or  hydrogen).  To  this  class  belong  the  neu- 
tral potash,  soda,  and  baryta-salts,  and  most  of  the  insoluble 
salts  of  tungstic  acid.  No  acid  salts  of  this  class  appear  to  exist. 
The  solution  of  an  ordinary  tungstate  dropped  into  excess  of 
dilute  nitric  acid  produces  a  gelatinous  precipitate.  The  hy- 
drated  tungstic  acid  obtained  by  the  action  of  aqua  regia  on 
wolfram  belongs  to  this  variety,  its  formula  being  WO3.HO. 

2.  ParatungstateSj  W^Oij-SMO,  with  or  without  water. 
To  this  class  belong  the  salts  commonly  called  bitungstates  of 
potash,  soda,  ammonia,  baryta,  &x;.  They  all,  excepting  the 
soda-salt,  dissolve  but  sparingly  in  water.  The  solutions  give 
no  precipitate  on  the  addition  of  very  small  quantities  of 
nitric  acid,  or  of  very  weak  hydrochloric  acid.  They  give 
precipitates  with  the  ammoniacal  solutions  of  nitrate  of  mag- 
nesia, zinc,  and  silver,  which  the  ordinary  tungstates  do  not. 

3.  MetatungstateSy  \V3O9.MO,  with  or  without  water.  The 
ammonia-salt  of  tliis  variety  is  formed  by  boiling  a  solution 
of  the  paratungstate  for  several  hours ;  the  solution  filtered 
when  cold  and  then  evaporated  to  a  syrup,  yields  very  soluble 
octohedrons.  The  solution  is  not  precipitated  by  concentrated 
hydrochloric  acid — 4.  Isotung states,  WjOg.MO,  with  or  with- 
out water.  The  ammonia-salt  is  formed  by  boiling  meta- 
tuugstate  of  ammonia  with  excess  of  ammonia;  it  is  but 
slightly  soluble  in  water.  The  acid,  which  may  be  separated 
from  it  by  means  of  another  acid,  is  principally  characterised 
by  reproducing  the  isotungstate  when  treated  with  ammonia. 
5.  Poly  tungstates  J  WgOig.SMO.  When  the  yellow  acid  ob- 
tained from  wolfram  is  treated  with  ammonia,  and  the  solution 
slowly  evaporated,  paratungstate  of  ammonia  is  first  deposited 
and  afterwards  the  isotungstate.    The  mother-liquor  separates 


TUNGSTATES.  181 

into  two  layers,  one  of  whicli  is  brown  and  syrupy,  and  changes 
on  drying  to  an  easily  soluble  crystalline  mass,  probably  a 
double  salt  of  ammonia  and  iron.  Boiled  with  strong  nitric 
acid,  it  yields  a  precipitate  which  is  not  gelatinous,  and  does 
not  turn  yellow  when  boiled.  Polystungstic  acid  is  further 
characterised  by  forming  with  ammonia  a  very  soluble  salt, 
which  becomes  gummy  on  evaporation.  6.  Laurent  also, 
mentioned  another  class  of  tungstates,  viz.,  Homotungstates, 
containing  WgO^g  .  MO.  According  to  Margueritte  *  also 
there  exist  acid  tungstates  containing  3,  4,  5  and  6  eq.  of 
acid  to  1  eq.  of  base. 

The  composition  of  the  tungstates  has  also  been  recently 
examined  by  W.  Lotz  f,  whose  results  differ  in  many  points 
from  the  preceding.  According  to  Lotz,  crude  tungstic  acid, 
obtained  from  wolfram  by  the  action  of  hydrochloric  and  a 
small  quantity  of  nitric  acid,  yields  by  digestion  with  ammo- 
nia and  evaporation  at  a  very  gentle  heat,  yellow  needles  of 
an  ammonia-salt  containing  3NH4O  .  7WO3  +  6H0,  or 
2(NH40.2W03)  +  NH4O  .  3WO3  +  6H0.  By  mixing  warm 
concentrated  solutions  of  1  eq.  of  monotungstate  of  soda,  and 
rather  more  than  1  eq.  chloride  of  ammonium,  a  double  salt 
is  obtained, composed  of  (2NH4O  .  WO3)  +  NaO .  WO3  +  3H0; 
and  by  adding  1  eq.  metatungatate  of  soda  to  a  boiling  solu- 
tion of  2  eq.  chloride  of  ammonium,  another  double  salt  is 
formed  containing  3NaO .  7WO3  +  4(3NH40 .  7WO3)  +  14H0. 
The  needle-shaped  ammonia- salt  mixed  wdth  solutions  of  the 
neutral  salts  of  barium,  strontium,  manganese,  nickel,  and 
lead,  yields  precipitates  of  the  general  formula  3MO  .  7WO3. 
With  alumina  a  white  curdy  precipitate  is  formed  containing 
AI2O3  .  7WO3  -f  9H0.  Sesquioxide  of  chromium  forms  a  salt 
of  a  similar  constitution.  With  magnesia,  a  sparingly  soluble 
crystalline  double  salt  is  formed,  containing  2(MgO  .  2WO3)  + 
NH4O  .  3W03H-  lOHO ;  a  similar  double  salt  with  zinc.   Cad- 

*  Ann.  Ch.  Phys.  [3],  xvii.  475. 
t  Ann.  Cli.  Phann.  xci.  49. 
K  3 


182  TUNGSTEN. 

mium  also  forms  a  double  salt  containing  SNH^O  .  7WO3  + 
4(3CdO  .  7W3O)  +  35HO.  To  the  octoliedral  tungstate  of  am- 
monia, "which  was  regarded  by  Margueritte  as  NH^O .  3WO3  + 
5  HO,    and    by   Laurent    as    a   metastungstate    containing 

(NH4)^H.W30,o  +  5IIO,or^^^^4^l   I8WO3  +  3OHO.  Lotz 

assigns  the  formula  2(NH40  .  4WO3)  +  15  eq.  The  solution  of 
this  salt  is  not  precipitated  by  nitric  or  hydrochloric  acid  at 
ordinary  temperatures,  but  after  continued  boiling  yields  a 
yellow  precipitate ;  but  if  it  be  previously  mixed  with  potash, 
the  addition  of  an  acid  produces  an  immediate  white  precipi- 
tate, which  turns  yellow  on  boiling ;  the  needle-shaped  salt 
gives  an  immediate  precipitate  with  acids,  witliout  previous 
addition  of  alkali.  The  octohedral  salt  diftcrs  from  the 
needle-shaped  salt  also,  in  not  forming  precipitates  with 
solutions  of  the  earths  and  other  metallic  oxides,  except  when 
previously  mixed  with  ammonia,  by  which,  indeed,  it  is  con- 
verted into  the  salt  3NH4O  .  TWOj. 

Sulphides  of  tungsten. — The  bisulphide  is  prepared  by  mix- 
ing one  part  of  tungsten  with  six  parts  of  cinnabar,  and 
exposing  the  mixture,  covered  witli  charcoal,  in  a  crucible,  to 
a  white  heat ;  or,  according  to  Roche,  by  fusing  bitung- 
state  of  potash  with  an  equal  weight  of  sulphur,  and  washing 
the  fused  mass  with  water.  The  tersulphide  is  formed  by 
dissolving  tungstic  acid  in  an  alkaline  sulphide,  and  precipi- 
tating  by  an  acid.  It  is  of  a  liver-brown  colour,  and  becomes 
black  on  drying.  The  tersulphide  of  tungsten  has  a  certain 
degree  of  solubility  in  water  containing  no  saline  matter,  and 
is  a  strong  sulphur-acid.  The  salt  KS.WS3  fonns  pale  red 
crystals.  Two  parts  of  this  sulphur-salt  dissolved  in  water 
with  one  part  of  nitre,  give  large  and  beautiful  ruby-red 
crystals  of  a  double  salt,  KS.\VS3H-KO.K05. 

Phosphides  of  tungsten.  —  Phosphorus  and  tungsten  com- 
bine directly,  but  without  emission  of  light  and  heat,  when 
finely  pounded  metallic  tungsten  contained  in  a  glass  tube  is 


CHLORIDES    OF    TUNGSTEN.  183 

lieated  to  redness  in  phosphorus  vapour.  The  resulting 
compound  is  a  dull,  dark  grey  powder,  very  difficult  to  oxidise, 
and  containing  W3P2-  Another  compound,  W^P,  is  obtained 
in  magnificent  crystalline  groups,  having  exactly  the  appear- 
ance of  natural  geodes,  by  reducing  a  mixture  of  2  eq.  phos- 
phoric and  1  eq.  tungstic  acids  at  a  very  high  temperature 
in  a  crucible  lined  with  charcoal.  The  crystals  are  six-sided 
prisms,  sometimes  an  inch  long,  of  a  steel-grey  colour,  and 
strong  lustre;  their  specific  gravity  is  5 '207.  This  compound 
is  a  perfect  conductor  of  electricity;  undergoes  no  change 
when  heated  to  the  melting  point  of  manganese  in  a  close 
vessel,  and  remains  nearly  unaltered  when  heated  to  redness 
in  the  air;  but  burns  with  great  splendour  on  charcoal  in  a 
stream  of  oxygen,  or  on  fused  chlorate  of  potash ;  it  is  not 
attacked  by  any  acid,  not  even  by  aqua-regia  (Wohler).* 

Bichloride  of  tungsten,  WCI2,  is  formed  when  metallic 
tungsten  is  heated  in  chlorine  gas.  It  condenses  in  dark  red 
needles,  which  are  very  fusible  and  volatile.  This  chloride  is 
decomposed  by  water,  and  tungstic  oxide  with  hydrochloric 
acid  formed. 

Terchloride  of  tungsten,  WCI3,  is  produced  at  the  same  time 
as  the  last  compound,  and  also  when  the  sulphide  of  tungsten 
is  heated  in  chlorine  gas.  It  forms  a  sublimate  of  beautiful 
red  crystals,  which  are  resolved  by  water  into  tungstic  and 
hydrochloric  acids.  A  chlorotungstic  acid,  or  double  com- 
pound of  terchloride  of  tungsten  and  tungstic  acid,  WO2CI, 
or  WCI3  .  2WO3,  is  prepared  by  heating  tungstic  oxide,  in 
chlorine  gas.  It  condenses  in  yellow  crystalline  scales  :  when 
suddenly  heated,  it  is  resolved  into  tungstic  acid,  bichloride 
of  tungsten,  and  chlorine.  Another  compound  is  known, 
containing  2WCI3  .  WO3  (Bonnet). 

According  to  A.  Richef,  the  terchloride  of  tungsten  is  the 
only  product  obtained  when  tungsten  is  heated  in  pure  dry 

*  Chem.  Soc.  Qu.  J.  v.  94.  f  Compt.  rend.  xlii.  203. 

N  4 


184  j:STIMATION    OF    TUNGSTEN. 

chlorine  gas  :  it  crystallises  in  needles,  not  of  a  red  but  of  a 
steel-grey  colour.  The  bichloride  is  formed  in  small  quan- 
tity, as  a  blackish-brown  mass,  by  heating  the  terchloride  in 
dry  hydrogen ;  and  the  red  oxychloride  WCI2O,  by  passing 
chlorine  gas  over  a  mixture  of  tungstic  acid  and  charcoal,  and 
distilHng  the  product  in  an  atmosphere  of  hydrogen. 

ESTIMATION    OF    TUNGSTEN,   AND    METHODS    OF    SEPARATING    IT 
FROM    THE    PRECEDING    METALS. 

Tungsten  is  always  estimated  in  the  form  of  tungstic  acid. 
When  this  acid  exists  in  a  solution  not  containing  any 
other  fixed  substance,  it  is  sufficient  to  evaporate  to  dryness 
and  ignite  the  residue.  The  tungstic  acid  is  then  obtained 
in  a  state  of  purity,  and  contains  79*7G  per  cent,  of  the  metal. 
Tungstic  oxide  is  easily  converted  into  tungstic  acid  by  fusion 
with  carbonate  of  soda. 

The  best  method  of  separating  tungstic  acid  from  the  fixed 
alkalies  is  to  treat  the  solution,  after  exact  neutralisation  with 
nitric  acid,  with  a  solution  of  mercurous  nitrate.  Mercurous 
tungstate  is  then  precipitated,  and  the  mercury  may  be  ex- 
pelled from  the  dried  precipitate  by  careful  ignition  in  a  good 
draught. 

The  separation  of  tungstic  acid  from  the  earths  may  be 
eflPected  by  decomposing  the  compound  with  nitric  acid,  and 
treating  the  decomposed  mass  with  carbonate  of  ammonia, 
which  dissolves  the  tungstic  acid. 

Tungstic  acid  may  be  readily  separated  from  many  metallic 
oxides,  such  as  the  oxides  of  iron,  manganese,  nickel,  cobalt, 
/fflc?,  &c.,  by  fusing  the  whole  Avith  carbonate  of  soda,  and 
digesting  the  fused  mass  with  water,  which  dissolves  the 
tungstic  acid  and  leaves  the  oxides  undissolved. 

From  titanic  acid,  tungstic  acid  is  separated  by  ammonia, 
which  dissolves  only  the  latter. 

The  best  mode  of  separating  tungstic  acid  from  chromic 


MOLYBDENUM.  185 

acid,  is  to  treat  the  concentrated  solution  with  excess  of 
hydrochloric  acid^  which  precipitates  the  greater  part  of  the 
tungstic  acid ;  then  boil  with  alcohol  to  reduce  the  chromic 
acid  to  chromic  oxide;  and  dissolve  the  tungstic  acid  by 
ammonia. 


SECTION    VI. 

MOLYBDENUM. 

Eq.  47-88  or  598*5  ;  Mo. 

This  metal  is  closely  allied  to  tungsten.  Its  native  sul- 
phide was  first  distinguished  from  plumbago  by  Scheele,  in 
1778;  and  a  few  years  afterwards^  molybdic  acid^  w^hich  he 
had  formed,  was  reduced,  and  molybdenum  obtained  from  it, 
by  another  Swedish  chemist,  Hjelm.  The  name  molybdenum 
is  derived  from  the  Greek  term  for  plumbago. 

The  oxides  of  molybdenum  are  easily  reduced,  when  exposed 
to  a  strong  heat  in  a  crucible  lined  with  charcoal,  but  the 
metal  itself  is  very  refractory.  Bucholz,  who  obtained  it  in 
rounded  buttons,  found  it  to  be  a  white  metal,  of  density 
between  8'615  and  8-636.  It  may  be  reduced  from  its  chlo- 
rides by  hydrogen,  like  tungsten  (p.  177.),  and  then  forms 
a  light  steel- grey  specular  deposit,  adhering  to  the  glass 
(Wohler).  It  is  not  acted  upon  by  hydrochloric,  hydro- 
fluoric, or  diluted  sulphuric  acid;  but  is  dissolved  by  con- 
centrated sulphuric  acid,  by  nitric  acid,  and  by'  aqua-regia. 
Hydrate  of  potash  does  not  dissolve  this  metal  in  the  humid 
way.  Molybdenum  combines  in  three  proportions  with  oxy- 
gen, forming  molybdous  oxide,  MoO,  molybdic  oxide,  MoO-y 
and  molybdic  acid,  M0O3. 

Molybdous  oxide,  MoO,  55-88  or  698-5.  —  This  oxide  is 
obtained   by  adding   to   the   concentrated   solution   of  any 


18G  MOLYBDENUM. 

molybdate,  so  mucli  hydrochloric  acid  as  to  redissolve  the 
molybdic  acid  which  is  at  first  thrown  down,  and  placing  zinc 
in  the  liquid ;  this  becomes  first  blue,  then  reddish-brown, 
and  finally  black,  and  contains  the  chloride  of  zinc  and  proto- 
. chloride  of  molybdenum.  To  separate  the  oxide  of  molyb- 
denum from  the  oxide  of  zinc,  ammonia  is  added  to  the  liquid 
in  quantity  no  more  than  sufficient  to  precipitate  the  former, 
while  the  latter  remains  in  solution.  The  molybdous  oxide 
carries  down  with  it  a  portion  of  oxide  of  zinc,  from  which  it 
may  be  freed  by  washing  with  ammonia :  it  is  thus  obtained 
as  a  hydrate  of  a  black  colour.  The  hydrate  of  molybdous 
oxide  dissolves  with  difficulty  in  acids,  forming  solutions 
which  are  almost  black  and  opaque,  and  which  do  not  yield 
crystallisable  salts.  These  solutions  yield  with  the  alkalies 
and  their  carbonates  a  brownish-black  precipitate  of  the 
hydrated  oxide,  insoluble  in  the  caustic  alkalies,  slightly 
soluble  in  the  neutral  carbonates,  but  readily  soluble  in  bicar- 
bonate of  potash  or  carbonate  of  ammonia.  HydrosulpJiuric 
acid  throws  down  a  brown-black  precipitate,  and  sidphide 
of  ammonium  a  yellowish-brown  precipitate  of  sulphide  of 
molybdenum,  easily  soluble  in  sulphide  of  ammonium.  FeiTo- 
cyanide  or  ferricyanide  of  potassium  forms  a  dark-brown 
precipitate,  insoluble  in  excess.  Phosphate  of  soda  forms  a 
brownish-white  precipitate.  Molybdous  oxide  resists,  after 
ignition,  the  action  of  all  acids. 

Molybdic  oxide,  MoOg ;  6388  or  798-5.  — This  oxide 
may  be  obtained  by  igniting  molybdate  of  ammonia  in  a 
covered  crucible,  but  mixed  with  a  little  molybdic  acid. 
It  is  better  procured  by  igniting  rapidly,  in  a  covered 
crucible,  a  mixture  of  anhydrous  molybdate  of  soda  (which 
may  contain  an  excess  of  soda)  with  sal-ammoniac.  Water 
poured  upon  the  fused  mass  dissolves  common  salt,  and  leaves 
a  brown  powder  almost  black.  But  molybdic  oxide  prepared 
in  this  way  is  insoluble  in  acids.     The  hydrated  oxide  may 


MOLYBDIC   ACID.  183? 

be  obtained  in  various  ways,  one  of  which  consists  in  digesting 
molybdic  acid  with  hydrochloric  acid  and  copper,  till  all  the 
molybdic  acid  is  dissolved.  From  the  solution,  which  is  of  a 
deep-red  colour,  molybdic  oxide  is  precipitated,  in  appearance 
exactly  similar  to  the  hydrated  sesquioxide  of  iron,  by 
ammonia  added  in  sufficient  excess  to  retain  all  the  oxide  of 
copper  in  solution.  The  hydrate  has  a  certain  degree  of 
solubility  in  pure  water,  and  should,  therefore,  be  washed 
with  solution  of  sal-ammoniac,  and  lastly  with  alcohol. 
This  hydrate  reddens  litmus  paper,  but  possesses  no  other 
property  of  an  acid.  It  is  not  dissolved  by  the  hydrated 
alkalies,  but  is  soluble  in  their  carbonates,  like  several  earths 
and  metallic  oxides.  It  dissolves  in  acids  and  forms  salts, 
which  are  red  when  they  contain  water  of  crystallisation,  and 
black  when  anhydrous.  The  aqueous  solutions  of  these  salts 
have  a  reddish-brown  colour,  and  a  rough,  somewhat  acid 
and  subsequently  metallic  taste.  When  heated  in  the  air, 
they  have  a  tendency  to  become  blue  by  oxidation.  With 
zinc,  they  first  blacken,  and  then  yield  a  black  precipitate  of 
hydrated  molybdous  oxide.  Their  behaviour  with  alkalies, 
hydrosulphuric  acid  &c.,  is  similar  to  that  of  the  molybdous 
salts,  excepting  that  the  precipitates  are  lighter  in  colour. 
The  oxalate  of  molybdic  oxide  may  be  obtained  in  crystals  by 
spontaneous  evaporation. 

Molybdic  acid,  M0O3 ;  71*88  or  898*5. — The  native  sulphide 
of  molybdenum,  in  fine  powder,  is  roasted  in  an  open  crucible, 
with  constant  stirring,  at  a  heat  not  exceeding  low  redness, 
so  long  as  sulphurous  acid  goes  off.  It  leaves  a  dull  yellow 
powder,  which  is  impure  molybdic  acid.  This  is  dissolved  in 
ammonia,  and  the  molybdate  of  ammonia  purified  by  evapora- 
tion, during  which  some  foreign  matters  are  deposited,  and 
crystallised.  The  crystallised  salt,  exposed  to  a  moderate 
heat,  so  as  to  avoid  fusion,  gives  off  its  ammonia,  and  leaves 
molybdic  acid  in  a  state  of  purity.     The  acid  thus  prepared  is 


188  MOLYBDENUM. 

a  white  and  light  porous  mass,  which  may  be  diffused  in 
water,  and  divides  into  little  crystalline  scales  of  a  silky  lustre. 
It  fuses  at  a  red  heat,  and  forms  on  cooling  a  straw-coloured 
crystalline  mass,  the  density  of  which  is  3*49.  This  acid  forms 
no  hydrate.  It  requires  570  times  its  weight  of  water  to  dis- 
solve it.  Before  being  ignited,  it  is  soluble  in  acids,  and 
forms  a  class  of  compounds,  in  which  it  appears  to  play  the 
part  of  base,  but  of  which  not  much  is  known.  When  boiled 
with  bitartrate  of  potash,  molybdic  acid  dissolves,  even  after 
being  fused  by  heat. 

"WTien  a  solution  of  bichloride  of  molybdenum  is  poured 
into  a  saturated  or  nearly  saturated  solution  of  molybdate  of 
ammonia,  a  blue  precipitate  falls,  which  is  a  molybdate  of 
molybdic  oxidCy  MO2.2MO3.  This  compound  is  likewise 
readily  formed  in  a  variety  of  other  circumstances. 

The  salts  of  molybdic  acid  are  colourless,  when  their  base 
is  not  coloured.  When  they  are  treated  with  other  acids, 
molybdic  acid  is  precipitated,  but  dissolves  in  an  excess  of 
the  acid.  It  forms  both  neutral  and  acid  salts  with  the 
alkalies.  Tliese  alkaline  molybdatcs  are  the  only  ones  that  are 
easily  soluble  in  water;  of  the  rest,  some  dissolve  sparingly, 
and  others  are  completely  insoluble.  Solutions  of  the  alka- 
line molybdatcs  are  coloured  yellow  by  hydrosulphuric  acid 
from  formation  of  a  siilphomolybdate  of  the  alkali-metal 
(MS,MoS3),  and  then  yield  with  acids  a  brown  precipitate  of 
tersulphide  of  molybdenum.  This  is  an  extremely  delicate 
test  for  molybdic  acid.  They  form  white  precipitates  with 
salts  of  the  earths,  and  precipitates  of  various  colours  with 
salts  of  the  heavy  metals ;  e.  g.  white  with  lead  and  silver 
salts ;  yellow  with  ferric  salts ;  and  yellowish- white  with 
merciirous  salts. — Protochloride  of  tin  produces  immediately 
a  greenish  blue  precipitate,  soluble  in  hydrochloric  acid 
forming  a  green  solution ;  which  turns  blue  on  the  addition 
of  a  very  small  quantity  of  the  tin-solution. — When  tribasic 
phosphoric  acid,  or  a  liquid  containing  it,  is  added  to  the 


MOLYBDATES.  189 

solution  of  molybdate  of  ammonia,  together  with  an  excess  of 
hydrochloric  acid_,  the  liquid  turns  yellow,  and  after  a  while 
deposits  a  yellow  precipitate  of  molybdic  acid  combined  with 
small  quantities  of  phosphoric  acid  and  ammonia.  This  pre- 
cipitate is  soluble  in  ammonia  and  likewise  in  excess  of  the 
phosphate.  The  reaction  is  therefore  especially  adapted  for 
the  detection  of  small  quantities  of  phosphoric  acid.  The 
bibasic  and  monobasic  phosphates  do  not  produce  the  yellow 
precipitate.  Arsenic  acid  gives  a  similar  reaction.  According 
to  Seligsohn*,  the  yellow  precipitate  is  sl  phosphomolybdate  of 
ammonia  2(Sl>illfi  .  PO5)  +  15(H0  .  4M0O3).  By  digesting  it 
in  a  dilute  solution  of  acetate  of  potash  or  soda,  crystal- 
line  double  salts   are  formed,  containing  2(3NH40.P05)  + 

^  q|.4Mo03J.      With  acetate   of   baryta,   a   double 

salt  is  formed,  containing  SNH^O.POg  +  30(BaO.MoO3);  and 
similarly  with  acetate  of  lead. 

Molybdic  acid  and  other  compounds  of  molybdenum  form 
a  colourless  bead  with  borax  and  phosphorus-salt  in  the  outer 
blowpipe  flame.  In  the  inner  flame,  they  form  a  brown 
bead  with  borax  and  a  green  bead  with  phosphorus-salt. 

Molybdates  of  potash. — The  monomolybdatCj  KO.M0O3,  i^ 
obtained  by  agitating  the  termolybdate  with-  an  alcoholic 
solution  of  potash  :  it  then  separates  as  an  oily  mass,  which, 
when  dried  over  lime  and  sulphuric  acid,  crystallises  in  four- 
sided  prisms  containing  2(KO.Mo03)  4-  HO.  It  is  also  ob- 
tained by  mixing  a  solution  of  molybdate  of  ammonia  with 
excess  of  carbonate  of  potash,  and  evaporating  to  a  syrup. 
Bimolybdate  of  potash  does  not  appear  to  exist.  When  a 
solution  of  molybdic  acid  in  carbonate  of  potash  is  mixed  with 
strong  nitric  or  hydrochloric  acid  till  a  slight  permanent  pre- 
cipitate is  produced,  the  liquid  after  a  while  yields  crystals  of 
a  salt  containing  4KO.9M0O3  +  6H0  :  and  this  salt  is  decom- 

*  J.  pr.  Cliem.  Ixvii.  474. 


190  MOLYBDENUM. 

posed  by  water  into  monomolybdate,  which  dissolves  readily, 
and  termolybdate  which  is  sparingly  soluble : 

2(4K0.9Mo03)  =  3(KO.Mo03)  +  5(K0.3Mo03). 

The  termolybdate  dissolves  easily  in  Ipoiling  water,  and  separates 
as  a  bulky  white  precipitate  when  the  solution  is  quickly 
cooled ;  but  by  slow  cooling  it  is  obtained  in  needles,  having 
a  beautiful  silky  lustre  and  containing  KO.3M0O3  +  3  HO. 
Nitric  acid  added  in  excess  to  a  solution  of  molybdic  acid  in 
carbonate  of  potash  throws  down  a  white  precipitate  consisting 
sometimes  of  quadromolybdate  and  sometimes  of  poitamo- 
lybdate  of  potash,  both  anhydrous  (Svanberg  and  Struve).* 

Monomohjbdatc  of  soda,  NaO.MoOa  +  2110,  is  obtained  by 
fusing  molybdic  acid  with  an  equivalent  quantity  of  carbonate 
of  soda.  It  is  easily  soluble  in  water,  and  crystallises  in  small 
rhombohcdrons,  which  melt  easily  and  give  off  their  water. 
The  bimolybdate,  Na0.2Mo03  +  IIO,  is  obtained  in  a  similar 
manner.  It  crystallises  in  needles,  and  dissolves  sparingly  in 
cold,  readily  in  boiling  water.  The  termolybdate  is  obtained 
by  adding  nitric  acid  to  a  solution  of  molybdic  acid  in  car- 
bonate of  soda,  as  a  bulky  white  precipitate,  more  soluble 
than  the  corresponding  potash-salt.  The  solution  yields  crys- 
tals containing  Na0.3Mo03  -f  7110.  Nitric  acid  added  in 
excess  to  a  solution  of  molybdate  of  soda  throws  down  nothing 
but  molybdic  acid  (Svanberg  and  Struve). f 

Monomolybdate  of  ammonia,  NH4O.M0O3,  obtained  by 
treating  molybdic  acid  in  excess  with  strong  solution  of 
ammonia  in  a  closed  vessel,  then  precipitating  with  alcohol, 
and  drying  over  quick  lime,  forms  microscopic  four-sided 
prisms,  which  are  anhydrous.  The  bimolybdate,  NH40.^Mo03, 
is  deposited  as  a  white  crystalline  powder  when  a  solution  of 
molybdic  acid  in  excess  of  ammonia  is  quickly  evaporated.  A 
solution  of  molybdic  acid  in  ammonia,  evaporated  by  heat  to 

*  Ann.  Cli.  Pharm.  Ixviii.  494.  f  Ann.  Cli.  Pliarm.  Ixviii.  404. 


MOLYfiDATES.  191 

the  crystallising  point,  or  left  to  evaporate  in  the  air_,  deposits 
large  transparent  six-sided  prisms  containing  NH4O.2M0O3 
+  NH4O.3M0O3  +  3H0  (Svanberg  and  Struve). 

Monomolybdate  of  baryta^  BaO.MoOa,  is  precipitated  as  a 
sparingly  soluble  crystalline  powder  gn  adding  chloride  of 
barium  to  a  solution  of  molybdic  acid  in  excess  of  ammonia* 
Baryta-salts,  containing  BaO.SMoOg  +  SHO  and  Ba0.2Mo03 
-f-  Ba023Mo03  +  6H0,  are  obtained  by  precipitating  the  cor- 
responding potash  and  ammonia-salts  with  chloride  of  barium. 
By  decomposing  monomolybdate  of  baryta  with  dilute  nitric 
acid,  an  acid  salt  is  formed  containing  Ba0.9Mo03  +  4HO  ; 
it  crystallises  in  small  six-sided  prisms,  fusible  and  insoluble 
in  water  (Svanberg  and  Struve). 

Monomolybdate  of  magnesia^  MgO.Mo03  4-  5H0,  is  obtained 
in  distinct  crystals  by  boiling  molybdic  acid  and  magnesia  alba 
with  water,  and  evaporating  the  filtrate;  it  gives  off  3  eq. 
water  at  212''  (Struve).* 

Molybdate  of  manganous  oxide,  MnO.Mo03  •\-  HO,  is  ob* 
tained  as  a  heavy  white  powder,  by  treating  carbonate  of 
manganese  with  termolybdate  of  potash  or  soda. 

Protosulphate  of  iron  added  to  a  solution  of  molybdate  of 
potash,  reduces  the  molybdic  acid  to  a  lower  state  of  oxida- 
tion j  but  if  chlorine  gas  be  passed  through  the  solution  at  the 
same  time,  a  bulky  precipitate  is  formed,  which,  when  dried  in 
the  air,  forms  a  light  yellow  powder,  consisting  oi  pentamo- 
lybdate  of  ferric  oxide,  re203.5Mo03  +  16H0. 

By  boiling  the  solution  of  termolybdate  of  potash  or  soda, 
or  acid  molybdate  of  ammonia,  with  hydrate  of  alumina,  man- 
ganic oxide,  ferric  oxide,  or  chromic  oxide,  and  evaporating  to 
the  crystallising  point,  double  salts  are  obtained.  The  com- 
position of  the  double  salts  containing  alumina,  ferric  oxide, 
or  chromic  oxide  with  potash  or  oxide  of  ammonium,  may 
be  represented  by  that  of  the  alumina  and  potash-salt,  viz., 

*  Ann.  Ch.  Pharm.  xcvi.  266. 


192  MOLYBDENUM. 

AI2O3.6M0O3  +  3(K0.2Mo03)  +  20HO.     The  potassio-man 
^amc  salt  contains  Mn203.6Mo03+  5(KO,2Mo03)  +  12H0. 
The  ammonio -manganic   salt  is  similarly   constituted.      The 
sodio-chromic  salt  contains  Cr203.6Mo03  +  3(Na0.2Mo03)  + 
21  HO  (Struve). 

Acid  molybdate  of  ammonia,  added  to  a  boiling  solution  of 
sulphate  of  copper,  throws  down  a  heavy  green  amorphous 
powder,  consisting  of  basic  molybdate  of  copper y  4CUO.3M0O3 
-1-  5H0.  By  adding  molybdate  of  ammonia  in  excess  to  a 
cold  solution  of  sulphate  of  copper,  a  double  salt  is  formed, 
consisting  of  CUO.2M0O3  +  NH4O.3M0O3  +  9H0.  It  is  a 
white-blue  crystalline  powder,  which  gives  off  4  eq.  of  water 
at  212°  and  4  eq.  more  at  266°  (Struve). 

Molybdate  of  lead,  PbO.Mo03,  is  formed  by  precipitating 
nitrate  of  lead  with  termolybdate  of  potash.  It  is  a  heavy 
white  powder  which  melts  only  at  a  high  temperature.  It 
occurs  finely  crystallised  as  a  mineral.  Chromate  of  lead  is 
dimorphous,  and  corresponds  in  the  least  usual  of  its  forms 
with  molybdate  of  lead :  hence  molybdenum  is  connected 
with  the  magnesian  metals,  and  tungsten  also  with  the  same 
class,  from  the  isomorphism  of  the  tungstates  and  molybdates. 

Sulphides  of  molybdenum. — The  bisulphide  is  the  ore  from 
which  the  compounds  of  this  metal  are  derived.  It  occurs  in 
many  parts  of  Sweden,  and  might  be  procured  in  quantity  if 
any  useful  application  of  the  metal  were  discovered.  It  is  a 
lead-grey  mineral,  having  the  metallic  lustre,  composed  of 
flexible  lamince.  soft  to  the  touch,  and  making  a  streak  upon 
paper  like  plumbago.  Nitric  acid  oxidates  it  easily,  without 
dissolving  it.  Its  density  is  from  4*138  to  4*569.  A  tersuU 
phide  of  mohjbdenum  is  obtained  in  the  same  way  as  the 
corresponding  compound  of  tungsten,  and  affords  crystallisa])le 
sulphur-salts  which  are  red.  The  sulphomolybdate  of  potas- 
sium combines  likewise  with  nitrate  of  potash.  When  a 
solution  of  the  former  salt  is  boiled  with  tersul phide  of  molyb- 
denum in  excess,  the  latter  is  converted  into  l^isulpliide  of 


ESTIMATION    OP     MOLYBDENUM.  193 

molybdenum,  and  a  quadrisulphide  of  molyhdenum  dissolves  in 
combination  with  the  sulphide  of  potassium.  The  quadrisul- 
phide may  be  precipitated  by  hydrochloric  acid,  and  when 
dried  is  a  cinnamon-brown  powder. 

Chlorides  of  molybdenum. — A  protochloride  is  formed  when 
molybdous  oxide  is  dissolved  in  hydrochloric  acid  j  the  bichlo- 
ride when  molybdenum  is  heated  dry  in  chlorine  gas,  as  a 
dark -red  gas  which  condenses  in  crystals,  like  those  of  iodine. 
It  forms  a  crystallisable  double  salt  with  sal-ammoniac. 
Chloromolybdic  acid,  or  a  compound  of  terchloride  of  molyb- 
denum and  molybdic  acid,  M0O2CI,  or  M0CI3 -1- 2M0O3,  is 
formed  with  (molybdic  acid),  when  molybdic  oxide  is  exposed 
to  chlorine  gas  at  a  red  heat.  It  sublimes  below  a  red  heat, 
and  condenses  in  crystalline  scales,  which  are  white  with  a 
shade  of  yellow. 


ESTIMATION    OP    MOLYBDENUM,     AND     METHODS    OP    SEPARATING 
IT    FROM    THE    PRECEDING    METALS. 

The  determination  of  molybdic  acid  is  more  difRcult  than 
that  of  tungstic  acid,  on  account  of  its  partial  volatility.  The 
best  mode  of  estimating  it  is  to  convert  it  into  molybdic  oxide 
by  ignition  in  an  atmosphere  of  hydrogen ;  the  oxide  which  is 
perfectly  fixed  may  then  be  weighed ;  it  contains  74*95  per 
cent,  of  the  metal.  When  molybdic  acid  exists  in  solution 
in  ammonia  or  in  other  acids,  the  solution  must  be  care- 
fully evaporated  to  dryness,  and  the  residue  treated  as  above. 

Molybdic  acid  is  separated  from  most  metallic  oxides  by  its 
solubility  in  sulphide  of  ammonium.  The  filtered  solution  is 
then  treated  with  an  excess  of  very  dilute  nitric  acid,  to 
precipitate  the  tersulphide  of  molybdenum ;  the  precipitate 
collected  on  a  weighed  filter,  and  its  quantity  determined ;  after 
which,  a  weighed  quantity  of  it  is  ignited  in  an  atmosphere  of 

VOL.  II.  o 


194  TELLURIUM. 

hydrogen,  to  convert  it  into  the  bisulphide,  MoS^,  from  the 
weight  of  which  the  amount  of  molybdenum  is  calculated. 

Molybdic  acid  is  separated  from  the  earths  by  fusing  with 
carbonate  of  soda,  and  digesting  the  fused  mass  in  water,  which 
dissolves  molybdate  of  soda,  and  leaves  the  earth  in  the  form 
of  carbonate. 

From  the  fixed  alkalies,  molybdic  acid  may  be  separated  by 
precipitation  with  mercurous  nitrate,  and  its  quantity  esti- 
mated from  the  weight  of  the  precipitate. 


SECTION    VII. 

TELLURIUM. 

^g.  64-14  or  801-8  J  Te. 

Tellurium  is  a  metal  of  rare  occurrence,  and  appeared  at  one 
time  to  be  almost  confined  to  certain  gold  mines  in  Transyl- 
vania; but  it  has  been  found  lately,  in  considerable  abun- 
dance, at  Schemnitz,  in  Hungary,  combined  with  bismuth; 
and  in  the  silver  mine  of  Sadovinski  in  the  Altai,  united  with 
silver  and  with  lead.  It  was  first  described  as  a  new  metal 
by  Klaproth,  who  gave  it  the  name  of  tellurium,  from  telluSj 
the  earth. 

Tellurium  is  chiefly  obtained  from  telluride  of  bismuth. 
The  ore,  after  being  freed  from  the  matrix  by  pounding  and 
washing,  is  mixed  with  an  equal  weight  of  carbonate  of 
potash  or  soda,  the  mixture  made  up  into  a  paste  with  olive 
oil,  and  heated  in  a  well  closed  crucible,  carefully  at  first  to 
prevent  frothing,  and  afterwards  to  a  full  white  heat.  The 
fused  mass  is  then  digested  in  water ;  which  leaves  the  bis- 
muth and  the  excess  of  charcoal  undissolved,  and  dissolves 
the  tellurium  in  the  form  of  telluride  of  potassium  or  sodium  ^ 
which  imparts  a  port-wine  colour  to  the  liquid.  The  solution 
deposits  metallic  tellurium  when  exposed  to  the  air,  or  more 


TELLURIUM.  195 

quickly  when  air  is  blown  througli  it ;  and  the  precipitated 
metal  is  purified  by  washing  with  acidulated  water,  and  sub- 
sequent distillation  in  an  atmosphere  of  hydrogen  (Berzelius) . 
The  metal  is  also  obtained  from  the  ore  called  foliated  tel- 
lur'nnn,  which  contains  13  per  cent,  of  tellurium^  and  63  per 
cent,  of  lead,  together  with  copper,  gold,  antimony,  and  sul- 
phur. The  finely  pounded  mineral  is  freed  from  the  sulphide 
of  lead  and  antimony  by  repeated  boiling  with  strong  hydro- 
chloric acid  and  washing  with  water;  the  residual  telluride  o^ 
gold  treated  with  strong  nitric  acid ;  the  tellurium -solution 
poured  off  from  the  gold  and  evaporated  to  dryness;  the 
residue  dissolved  in  hydrochloric  acid ;  and  the  tellurium  pre- 
cipitated from  the  solution  by  sulphurous  acid  (Berthier).  * 

In  a  state  of  purity,  tellurium  is  silver- white  and  very  bril- 
liant. It  is  very  crystallisable,  assuming  a  rhombohedral  form, 
in  which  it  is  isomorphous  with  arsenic  and  antimony.  It  is 
brittle  for  a  metal,  and  an  indifferent  conductor  of  heat  and 
electricity.  Its  density  is  from  6*2324  to  6*2578,  according 
to  Berzelius.  Tellurium  is  about  as  fusible  as  antimony,  and 
may  be  distilled  at  a  high  temperature.  It  burns  in  air,  at 
a  high  temperature,  with  a  lively  blue  flame,  green  at  the 
borders,  and  diffuses  a  dense  wiiite  smoke,  which  generally  has 
the  odour  of  decaying  horse-radish,  from  the  presence  of  a 
little  selenium.  Tellurium  belongs  to  the  sulphur-class  of 
elements.  Like  selenium  and  sulphur,  it  dissolves  to  a  small 
extent  in  concentrated  sulphuric  acid,  and  communicates  to  it 
a  fine  purple-red  colour.  In  this  solution,  the  metal  is  not 
oxidated,  for  it  is  precipitated  again,  in  the  metallic  state,  by 
water.  This  metal  has  also  considerable  analogy  \vith  anti- 
mony, and  may  probably  connect  together  the  sulphur  and 

*  For  further  details  respecting  the  extraction  of  tellurium,  vide  Berzelius, 
Traite  de  Chiruie,  i.  344;  and  the  translation  of  Gmelin's  Handbook,  iv.  303. 
Wohler  states,  in  a  note  to  his  paper  on  telluride  of  ethyl  (Ann.  Cli.  Pharra. 
Ixxxiv.  70),  that  tellurium  may  be  obtained  in  considerable  quantities  from  the 
residues  of  the  Transylvanian  gold-extraction,  which  have  hitherto  been  throwa 
away  as  worthless. 

o  2 


196  TELLURIUM. 

phosphorus  families.  Tellurium  combines  in  two  propor- 
tions with  oxygen,  forming  tellurous  acid,  Te02,  ^^^  telluric 
acid,  TeOg. 

Tellurous  acid,  TeOa  ;  80-14  or  1001-8.— This  acid  differs 
remarkably  in  properties  according  as  it  is  anhydrous  or 
hydrated.*  Hydrated  tellurous  acid  is  obtained  by  pre- 
cipitating bichloride  of  tellurium  with  cold  water;  or  by 
fusing  anhydrous  tellurous  acid  with  an  equal  weight  of 
carbonate  of  potash,  as  long  as  carbonic  acid  is  disengaged, 
dissolving  the  tellurite  of  potash  in  water,  and  adding  nitric 
acid  to  it  till  the  liquor  distinctly  reddens  litmus  paper.  A 
white  and  bulky  precipitate  is  produced,  which  is  washed  with 
ice-cold  water,  and  afterwards  dried  without  artificial  heat. 
Tellurium  likewise  dissolves  with  violence  in  pure  nitric  acid 
of  density  1*25,  and  if  after  the  first  five  minutes,  the  clear 
liquid  be  poured  into  water,  tellurous  acid  is  precipitated  in 
white  flocks.  But  if  not  immediately  precipitated,  the  nitric 
acid  solution  undergoes  a  change. 

The  hydrated  acid  obtained  by  these  processes  forms  a 
light,  white,  earthy  mass,  of  a  bitter  and  metallic  taste.  It 
instantly  reddens  litmus  paper,  and  while  still  moist,  dissolves 
to  a  sensible  extent  in  water.  It  is  very  soluble  in  acids,  and 
the  solutions  are  not  subject  to  change,  except  that  which  is 
formed  by  nitric  acid.  Ammonia  and  the  alkaline  carbonates 
also  dissolve  hydrated  tellurous  acid  with  facility,  the  latter 
becoming  bicarbonates. 

Anhydrous  tellurous  acid. — When  the  solution  of  tellurous 
acid  in  water  is  heated  to  140°,  it  deposits  the  anhydrous  acid 
in  grains,  and  loses  its  acid  reaction.  The  same  change  occurs 
when  an  attempt  is  made  to  dry  the  hydrated  tellurous  acid 
by  heat :  it  parts  with  combined  water,  and  becomes  granular. 
The  solution  of  tellurous  acid  in  nitric  acid  changes  spon- 

*  "Berzelius  regarded  the  hydrated  and  anhydrous  acids  as  containing  dif- 
ferent modifications  of  the  same  compomid,  and  distinguished  them  as  a-tel- 
lurous  and  /S-telhirous  acid. 


TELLURITES.  197 

tar  ecusly  in  a  few  hours,  and  in  a  quarter  of  an  hour  when 
heat  is  applied  to  it,  and  allows  the  anhydrous  acid  to  precipi- 
tate. When  the  deposition  of  the  acid  is  slow,  it  forms  a 
crystalline  mass  of  fine  grains,  among  which  octohedral  crys- 
tals may  be  perceived  by  the  microscope.  The  acid  is  then 
anhydrous.  In  this  state  it  does  not  redden  litmus,  or  not  till 
after  a  time.  It  is  but  very  slightly  soluble  in  water,  and  the 
solution  has  no  acid  reaction.  At  a  low  red  heat,  it  fuses  into 
a  clear  transparent  liquid  of  a  deep  yellow  colour,  which  on 
cooling  becomes  a  white  and  highly  crystalline  mass,  easily 
detached  from  a  crucible.  Tellurous  acid  is  volatile,  although 
less  so  than  the  metal  itself. 

The  solutions  of  hydrated  tellurous  acid  in  the  stronger 
acids  yield  a  black  precipitate  of  metallic  tellurium,  when 
treated  with  powerful  deoxidising  agents,  such  as  zinc,  phos- 
phorus, protochloride  of  tin,  sulphurous  acid,  and  the  alkaline 
bisulphates.  Hydrosulphuric  acid  and  sulphide  of  ammonium 
throw  down  black-brown  sulphide  of  tellurium,  easily  soluble 
in  excess  of  sulphide  of  ammonium. 

The  tellurites,  or  compounds  of  tellurous  acid  with  salifiable 
bases,  contain  1  atom  of  base  united  with  1,  2,  or  4  atoms  of 
acid.  They  are  fusible,  and  generally  solidify  in  the  crystalline 
form  on  cooling ;  the  quadrotellurites,  however,  form  a  glass. 
Tellurites  are  colourless  unless  they  contain  a  coloured  base ; 
those  which  are  soluble  have  a  metallic  taste.  Most  of  them, 
when  heated  to  redness  with  charcoal,  yield  metallic  tellurium, 
sometimes  with  slight  detonation ;  and  the  reduced  metal 
volatilises  readily,  being  at  the  same  time  reoxidised  and 
forming  a  Avliite  deposit  on  the  charcoal ;  it  likewise  imparts 
a  green  colour  to  the  flame ;  the  tellurites,  when  ignited  with 
potassium,  or  with  charcoal  and  carbonate  of  potash,  yield 
telluride  of  potassium  which  dissolves  in  water,  forming  a  port- 
wine  coloured  solution ;  with  the  zinc  and  silver-salts,  how- 
ever, and  a  few  others,  this  reduction  does  not  take  place. 
The  tellurites  of  ammonia,  potash  and  soda  are  easily  soluble 


198  TELLURIUM. 

in  water;  those  of  baryta,  strontia,  and  lime  are  sparingly 
soluble ;  the  rest,  insoluble.  An  aqueous  solution  of  a  tellu- 
rite is  decomposed  by  the  carbonic  acid  of  the  air.  Nearly  all 
tellurites  dissolve  in  strong  hydrochloric  acid  without  evolv- 
ing chlorine  when  heated ;  tlie  solution  exhibits  the  above- 
mentioned  characters  of  a  solution  of  tellurous  acid  in  the 
stronger  acids,  except  in  so  far  as  it  may  be  interfered  with  by 
the  presence  of  another  base.  The  solution  when  diluted  in 
water  yields  a  white  precipitate  of  tellurous  acid,  provided 
the  excess  of  hydrochloric  acid  present  is  not  too  great. 

Monotellurite  of  potash j  KO .  TeOg,  is  obtained  by  heating 
1  eq.  tellurous  acid  with  eq.  of  carbonate  of  potash.  The 
fused  mass  on  cooling  forms  crystals  of  large  size.  The  salt 
dissolves  slowly  in  cold,  more  quickly  in  warm  water,  llitel- 
lurite  of  potash,  KO-TcjO^,  is  obtained  by  fusing  two  atoms 
of  tellurous  acid  with  one  atom  of  carbonate  of  potash.  It 
appears  to  be  capable  of  existing  in  a  hot  solution,  and  of 
crystallising  in  certain  circumstances ;  but  it  is  decomposed 
by  cold  water,  which  resolves  it  into  the  neutral  salt,  which 
dissolves,  and  a  quadritelhirite  of  potash,  KO.Tc^Og  -f  1-H0. 
The  latter  salt  cannot  be  redissolved  in  water,  without  de- 
composition. In  losing  its  water  when  heated,  it  swells  up 
like  borax. 

Telluric  acid,  TeO,;  88  14  or  1101 -8.— This  acid  is  obtained 
in  combination  with  potash,  by  fusing  tellurous  acid  with 
nitre.  It  may  then  be  transferred  to  baryta,  and  the  insoluble 
telluratc  of  baryta  decomposed  by  sulphuric  acid.  The  solu- 
tion of  telluric  acid  gives  bulky,  hexagonal,  prismatic  crystals. 
Its  taste  is  not  acid,  but  metallic,  resembling  that  of  nitrate 
of  silver.  Indeed,  it  appears  to  be  but  a  feeble  acid,  redden- 
ing litmus  but  slightly,  when  the  solution  is  diluted.  The 
crystallised  acid  contains  3110,  of  which  it  loses  2H0  by 
efflorescence,  a  little  above  212°.  It  then  appears  insoluble  in 
cold  water,  but  may  be  completely  redissolved  by  long  digestion, 
particularly  with  ebullition,  and  is  not  permanently  altered. 


TELLURIC    ACID.  1C9 

Anhydrous  telluric  acid.  —  The  crystals  of  hydrated  telluric 
acid  give  off  all  their  water  at  a  heat  below  redness,  and  are 
converted  into  a  mass  of  a  fine  orange-yellow  colour,  without 
changing  their  form.  This  yellow  matter,  which  is  distin- 
guished, as  alpha-tellaric  acid  by  Berzelius,  is  remarkable  for 
its  indifference  to  chemical  reagents,  being  completely  in- 
soluble in  cold  or  boiling  water,  in  hot  hydrochloric  and 
nitric  acids,  and  in  potash-ley.  At  a  high  temperature,  it  is 
decomposed,  evolving  oxygen,  and  leaving  tellurous  acid  white 
and  pulverulent. 

Telluric  acid  has  but  slight  affinity  for  bases.  The  hydrated 
acid  withdraws  from  alkaline  carbonates,  only  so  much  alkali 
as  to  form  a  biacid  salt.  Telluric  acid  forms  bibasic,  sesqui- 
basic,  monobasic,  biacid,  and  quadracid  salts.  The  tellurates 
are  colourless,  unless  they  contain  a  coloured  base.  At  a  red 
heat,  they  give  off  oxygen  and  are  converted  into  tellurites. 
Before  the  blowpipe,  they  behave  like  tlie  tellurites ;  also  with 
reducing  agents,  such  as  protochloride  of  tin,  and  sulphurous 
acid,'  excepting  that  the  reduction  does  not  take  place  so 
quickly,  and  in  some  cases  requires  the  application  of  heat. 
Ilydrosulphuric  acid,  added  to  the  solution  of  a  tellurate, 
produces  no  change  at  first ;  but  if  the  liquid  be  placed  in  a 
stoppered  bottle  and  left  for  a  while  in  a  warm  place,  a  brown 
precipitate  of  sulphide  of  tellurium  is  formed.  Tellurates 
dissolve  in  cold  strong  hydrochloric  acid  without  decomposi- 
tion. The  solutions  are  not  yellow,  like  those  of  the  tel- 
lurites in  hydrochloric  acid,  and  may  be  diluted  with  water 
without  becoming  milky,  even  though  the  excess  of  hydro- 
chloric acid  be  but  small.  But  on  boiling  the  solution, 
chlorine  is  evolved,  and  the  liquid,  if  subsequently  mixed 
with  water,  gives  a  precipitate  of  tellurous  acid,  provided  the 
excess  of  hydrochloric  acid  is  not  too  great. 

Neutral  tellurate  of  potash  is  KO.TeOg  +  5H0;  the  bitel- 
lurate  of  pot  ash ,  KO.Te206  +  4H0  ;  the  quadritellurate  of 
potash,  K0.Te^0i2  +  4H0.     All  these  salts  may  be  obtained 


200  TELLURIUM. 

directly,  in  the  humid  way,  by  dissolving  the  proper  pro- 
portions of  hydrated  acid  and  carbonate  of  potash  together, 
in  hot  water.  A  portion  of  the  combined  water  in  the  last 
two  salts  is  unquestionably  basic,  but  how  much  of  it  is  so 
has  not  been  determined.  They  cannot  be  made  anhydrous 
by  heat  without  being  essentially  altered  in  properties. 

The  neutral  tellurate  of  potash  undergoes  no  change  in 
constitution  under  the  influence  of  heat,  resembling  in  that 
respect  those  tribasic  phosphates  of  which  the  whole  three 
atoms  of  base  are  fixed.  The  bi tellurate  of  potash  loses  its 
water  and  becomes  yellow  at  a  temperature  below  redness, 
and  is  changed  into  a  quadritellurate,  which  is  insoluble  both 
in  water  and  in  dilute  acids.  Water  dissolves  out  neutral  tel- 
lurate from  the  yellow  mass.  The  insoluble  salt  is  named,  by 
Berzelius,  the  alpha-quadritellurate  of  potash.  The  elements 
of  this  compound  are  united  by  a  powerful  affinity.  It  is 
formed  when  hydrated  telluric  acid  is  intimately  mixed  with 
a  potash-salt,  such  as  nitre  or  chloride  of  potassium,  and  the 
mixture  calcined  at  a  temperature  which  should  be  much 
below  a  red  heat ;  also  when  tellurous  acid  is  ignited  with 
chlorate  of  potash,  and  in  other  circumstances.  Hydrate  of 
potash  dissolves  the  alpha-quadritellurate  by  fusion,  and  nitric 
acid  by  a  long  continued  ebullition  ;  but  in  both  cases,  the 
acid  set  free  in  the  solution  exhibits  the  properties  of  ordinary 
telluric  acid. 

Telluretted  hydrogen^  Hydrotellmric  acid,  TeH,  is  a  gaseous 
compound  of  tellurium  and  hydrogen,  analogous  in  constitu- 
tion and  properties  to  sulphuretted  hydrogen.  It  is  obtained 
by  fusing  tellurium  with  zinc  or  with  tin,  and  acting  on  the 
mixture  with  hydrochloric  acid. 

Definite  sulphides  of  tellurium  have  been  obtained,  corre- 
sponding with  tellurous  and  telluric  acids.  They  are  sulphur- 
acids. 

Two  chlorides  of  tellurium  have  been  formed,  a  protochloride, 
TeCl,  to  which  there  is  no  corresponding  oxide,  and  a  bichlo- 


ESTIMATION    OP    TELLURIUM.  201 

ride,  TeCl2.  No  higher  chloride_,  corresponding  with  telluric 
acid,  has  been  obtained. 

Tellurium  forms  alloys  with  several  metals,  e.g.,  with  potas- 
sium, sodium,  aluminum,  bismuth,  zinc,  tin,  lead,  iron,  copper, 
mercury,  silver,  and  gold.  Some  of  these  alloys,  as  those  of 
bismuth,  silver,  and  gold,  are  found  native. 

Telluride  of  potassium  is  prepared  by  mixing  1  part  of  tel- 
lurium powder  with  10  parts  of  burnt  tartar ;  introducing  the 
mixture  into  a  porcelain  retort  fitted  with  a  glass  tube  bent 
downwards  at  right  angles ;  heating  the  retort  to  redness  for 
three  or  four  hours,  as  long,  indeed,  as  carbonic  oxide  con- 
tinues to  escape ;  and  then  introducing  the  end  of  the  bent  tube 
into  a  flask  kept  full  of  carbonic  acid  gas,  to  prevent  access  of 
air ;  this  latter  precaution  is  necessary  on  account  of  the  highly 
pyrophoric  character  of  the  product  (Wohler) .  The  compound 
may  also  be  obtained  by  heating  tellurium  with  potassium,  in 
a  retort  filled  with  hydrogen ;  combination  then  takes  place 
attended  with  vivid  combustion.  TeUuride  of  potassium  dis- 
solves in  water,  forming  a  port- wine  coloured  solution,  which 
on  exposure  to  the  air  becomes  decolorised,  and  deposits 
tellurium  in  shining  scales ;  with  acids  it  evolves  teUuretted 
hydrogen  gas.  Telluride  of  sodium  is  prepared  by  similar 
methods,  and  possesses  similar  properties. 


ESTIMATION    OF    TELLURIUM,    AND     METHODS    OF    SEPARATING    IT 
FROM    THE    PRECEDING    METALS. 

When  tellurium  exists  in  solution  in  the  form  of  t^llurous 
acid  it  is  reduced  to  the  metallic  state  by  sulphurous  acid  or  an 
alkaUne  bisulphite.  The  reduced  tellurium  is  then  collected  on 
a  weighed  filter,  and  carefully  dried  at  gentle  heat.  If  the 
solution  is  alkaline,  it  must  be  previously  acidulated  with 
hydrochloric  acid ;  if  it  contains  nitric  acid,  which  might  redis- 
solve  a  portion  of  the  precipitated  tellurium,  it  must  be  boiled 

YOL.  II.  p 


202  TELLURIUM. 

with  hydrochloric  acid  till  all  the  nitric  acid  is  decomposed, 
then  diluted  with  water,  and  treated  with  sulplmrous  acid  as 
above.  If  the  tellurium  is  in  the  state  of  telluric  acid,  that 
compound  must  first  be  reduced  to  tellurous  acid  by  boiling 
with  hydrochloric  acid,  and  the  tellurium  then  reduced  by 
sulphurous  acid. 

Tellurium  may  be  separated  from  the  alkalies  and  earths, 
and  from  manganese,  iron,  cobalt,  nickel,  zinc,  and  chromium, 
by  means  of  hydrosulphuric  acid.  If  the  precipitated  sulphide 
of  tellurium  is  quite  pure  and  definite,  it  may  be  collected  on 
a  weighed  filter,  dried  and  weighed,  and  the  amount  of  tellu- 
rium calculated  from  it.  But  if  it  contains  excess  of  sulphur, 
which  is  often  the  case,  it  must  be  boiled  with  aqua-regia  till 
it  is  completely  decomposed ;  the  solution  filtered  from  the 
separated  sulphur ;  freed  from  nitric  acid  in  the  manner  above 
described ;  and  the  tellurium  precipitated  by  sulphurous  acid. 

The  separation  of  tellurium  from  cadmium,  copper,  and  lead, 
may  be  effected  by  means  of  sulphide  of  ammonium,  in  which 
the  sulphide  of  tellurium  is  easily  soluble.  The  filtered  solu- 
tion is  then  treated  mth  excess  of  hydrochloric  acid  to  pre- 
cipitate the  sulphide  of  tellurium,  which  is  then  decomposed 
by  aqua-regia  as  just  described.  Tellurium  may  be  separated 
from  tin  in  solution  by  means  of  sulphurous  acid. 

The  quantity  of  metallic  tellurium  in  an  aUoy  may  be 
estimated  by  heating  the  alloy  in  a  current  of  chlorine  gas ; 
passing  the  volatile  chloride  of  tellurium  into  water  acidulated 
with  hydrochloric  acid,  which  dissolves  it ;  and  reducing  the 
tellurium  by  sulphurous  acid. 


ARSENIC. 


203 


ORDER  VI. 

METALS   ISOMOEPHOUS   WITH   PHOSPHORUS. 

SECTION    I. 

ARSENIC. 

Eq.  75  or  9375. 

This  metal  is  found  native,  but  more  generally  in  combina- 
nation  with  other  metals,  particularly  cobalt  and  nickel, 
and  is  largely  condensed,  during  the  roasting  of  their 
ores,  in  the  state  of  arsenious  acid.  The  metal  may  be  easily 
obtained,  in  a  state  of  purity,  by  subliming  a  portion  of 
native  arsenic  in  a  glass  tube  or  retort,  by  the  heat  of  a  lamp, 
or  by  reducing  a  mixture  of  one  part  of  arsenious  acid  and 
three  parts  of  black  flux,  in  the  same  apparatus.  The  metal 
in  condensing  forms  a  crust,  of  a  steel-grey  colour  and  bright 
metallic  lastre.  It  has  been  observed  to  crystallise  by  subli- 
mation in  rhombohedral  crystals,  and  is  isomorphous  with 
tellurium  and  antimony.  It  is  a  brittle  metal,  and  very  easily 
pulverised.  The  density  of  arsenic  is  from  5  to  5*96.  It 
rises  in  vapour  at  356°  (180°  Cent.)  without  first  undergoing 
fusion.  Arsenic  vapour  is  colourless;  its  density  is  10*370; 
and,  like  phosphorus  and  oxygen,  its  combining  measure  is  one 
volume.  It  has  as  strong  an  effect  upon  the  organ  of  smell 
as  selenium;  its  odour  resembles  that  of  garlic.  Arsenic 
combines  in  three  proportions  with  oxygen,  forming  by  spon- 
taneous oxidation  in  air  a  grey  sub-oxide,  the  composition  of 
which  is  undetermined;  it  also  forms  arsenious  and  arsenic 
acids,  AsOg  and  AsOg. 

VOL.  II.  Q 


201-  ARSENIC. 

Arsenious  acid,  99  or  1237*5. — This  compoimd  is  formed 
wlien  metallic  arsenic  is  volatilised  in  contact  mth  the  air. 
It  is  obtained  in  large  quantity,  as  an  accessary  product,  in 
the  roasting  of  arsenical  ores  of  tin,  cobalt,  and  nickel,  and 
as  principal  product  in  the  roasting  of  arsenical  pyrites. 
These  operations  are  performed  in  reverberatory  furnaces, 
communicating  with  chambers  in  which  the  arsenious  acid 
condenses.  The  product  is  purified  by  a  second  sublimation 
in  vessels  of  cast-iron,  or,  on  a  small  scale,  in  glass  or  earthen 
retorts. 

Arsenious  acid  heated  in  a  tube  closed  at  both  ends  melts 
into  a  colourless  liquid ;  but  under  the  ordinary  atmospheric 
pressure,  it  volatilises  at  about  380°  (at  444°  according  to 
Mitchell),  without  previous  fusion,  producing  a  colourless 
vapour,  which  has  a  density  of  13850,  and  is  therefore  com- 
posed of  1  volume  of  arsenic  vapour  and  3  volumes  of  oxygen, 
condensed  into  1  volume.  The  vapour  is  inodorous  when 
pure,  but  if  the  acid  be  volatilised  in  contact  with  any  easily 
oxidisable  substance,  as  when  it  is  thrown  on  red-hot  coals  or 
iron,  the  garlic  odour  of  metallic  arsenic  becomes  perceptible. 
In  the  solid  state,  arsenious  acid  exhibits  three  modifi- 
cations, one  amorphous,  and  two  crystalline.  (1.)  When  the 
sides  of  the  vessel  in  which  the  acid  is  distilled  become 
strongly  heated,  the  vapour  condenses,  at  a  temperature  near 
the  melting  point  of  the  acid,  into  a  transparent  vitreous  mass, 
having  a  conchoidal  fracture.  (2.)  When  arsenious  acid  is 
sublimed  in  a  glass  tube,  or  under  any  circumstances  which 
allow  the  vapour  to  condense  suddenly,  and  solidify  at  once, 
without  passing  through  the  semi-fused  state,  it  assumes  the 
form  of  regular  octohcdrons,  which,  if  the  sublimation  be 
slowly  conducted,  are  distinct,  and  have  an  adamantine  lustre. 
Similar  octohedral  crystals  are  obtained  when  arsenious  acid 
separates  from  its  solution  in  water  or  in  ammonia.  (3.)  In 
the  roasting  of  arsenical  cobalt  ores,  arsenious  acid  is  some- 
times obtained  in  the  form  of  thin  transparent  flexible  plates, 


ARSENIOUS    ACID.  205 

derived  from  a  right  rhombic  prism  (Wohler).  Crystals  of 
similar  form  are  obtained  by  saturating  a  boiling  solution  of 
caustic  potash  with  arsenious  acid,  and  then  leaving  it  to  cool 
or  mixing  it  with  water  (Pasteur) .  Vitreous  arsenious  acid, 
even  when  completely  protected  from  air  and  moisture, 
gradually  loses  its  transparency,  and  becomes  an  opaque 
white  mass,  passing  in  fact  into  the  octohedral  variety. 

The  specific  gravity  of  transparent  vitreous  arsenious  acid 
is  3*7385,  that  of  the  octohedral  variety  3*699  (Guibourt). 
The  vitreous  acid  dissolves  in  water  more  quickly  and  more 
abundantly  than  the  opaque  crystalline  acid ;  the  same  quan- 
tity of  water  which  at  54°  or  55°  will  take  up  36  or  38  parts 
of  the  former,  will  not  take  up  more  than  12  or  14  of  the 
latter  (Bussy).  According  to  Guibourt,  on  the  contrary,  100 
parts  of  boiling  water  dissolve  9*68  parts  of  the  vitreous,  and 
11*47  of  the  opaque  acid;  and  when  the  solutions  are  left  to 
cool  to  60°,  the  first  retains  1*78  parts,  and  the  latter  2*9  parts 
of  the  acid.  The  discrepancy  of  these  statements  and  of 
various  others  respecting  the  solubility  of  arsenious  acid,  may 
perhaps  be  reconciled  by  the  great  facility  with  which  the 
amorphous  variety  passes  into  the  crystalline,  and  vice  versa. 
It  appears  indeed  that  heat  tends  to  transform  the  opaque  into 
the  vitreous  acid,  and  cold  to  produce  the  contrary  change, 
and  this  tendency  is  manifested  even  in  presence  of  water. 
Thus  the  opaque  acid  is  converted  into  the  vitreous  by  long 
boiling  ^Yith.  water,  the  contrary  change  taking  place  gradually 
in  the  solution  when  cold. 

The  aqueous  solution  of  arsenious  acid  is  transparent  and 
colourless,  and  reddens  litmus  slightly.  Hydrosulphuric  add 
colours  it  yellow,  and  on  the  addition  of  hydrochloric  acid 
throws  down  a  yellow  precipitate  of  AsSg.  On  the  addition 
of  a  small  quantity  of  ammonia,  it  gives  a  yellow  precipitate 
with  nitrate  of  silver,  and  a  peculiar  light  green  (Scheele^s 
green)  with  sulphate  of  copper ;  these  precipitates  are  easily 
soluble  in  excess  of  ammonia.     Mixed  vrith  hydrochloric  acid 

Q  2 


206  ARSENIC. 

it  produces  a  grey  metallic  deposit  on  copper.  With  zinc  and 
sulphuric  or  hydrochloric  acid,  it  evolves  arseniuretted 
hydrogen  gas  (p.  211.). 

Arsenious  acid  dissolves  in  many  acids,  in  hydrochloric 
acid  for  example,  with  much  greater  facility  than  in  water, 
but  without  forming  any  definite  compounds.  It  is  dissolved, 
however,  by  bitartrate  of  potash,  with  formation  of  a  crys- 
tallisable  salt  analogous  to  the  potash-tartrate  of  antimony. 
The  vitreous  acid  dissolved  in  boiling  dilute  hydrochloric  acid 
crystallises  on  cooling  in  regular  octohcdrons,  the  deposition 
of  each  crystal  being  accompanied  by  a  flash  of  light.  Agita- 
tion increases  the  number  of  crj^stals  produced,  and  the 
intensity  of  the  light.  The  opaque  acid  dissolved  in  hydro- 
chloric acid  does  not  emit  any  light  on  crystallising ;  the  same 
is  the  case  with  the  crystals  obtained  by  cooling  a  solution  of 
the  vitreous  acid  in  hydrochloric  acid,  when  these  crystals  are 
redissolved  in  hydrochloric  acid.  Hence  it  appears  that  the 
vitreous  acid  dissolves  as  such  in  hydrochloric  acid,  and  that 
the  emission  of  light  at  the  moment  of  crystallisation  is  due 
to  the  change  from  the  amorphous  to  the  crystalline  state. 

Arsenious  acid  is  dissolved  by  potash y  soda,  and  ammonia, 
also  by  alkaline  carbonates,  but  from  these  latter  solu- 
tions it  is  sometimes  deposited  in  the  free  state,  so  that  it  is 
doubtful  whether  arsenious  acid  displaces  carbonic  acid  in  the 
humid  way.  The  ai'senites  of  the  earths  and  metallic  oxides 
are  insoluble  in  water,  but  soluble  in  acids. 

With  potash,  arsenious  acid  forms  the  salts  2K0 .  AsOg, 
KO  .  ASO3,  and  KO  .  HO  .  2ASO3 ;  similar  salts  with  soda. 
With  baryta,  it  forms  2BaO  .  AsOg  and  BaO  .  AsOg ;  and 
with  lime,  2CaO  .  AsOg.  With  nickel,  cobalt,  and  silver,  it 
forms  bibasic  and  sesquibasic  salts. 

The  neutral  solutions  of  the  alkaline  arsenites  give  a  yellow 
precipitate  with  nitrate  of  silver,  and  Scheele's  green  with 
copper  salts.     Acidulated  with  hydrochloric  acid,  they  give 


ARSENIC    ACID.  207 

with  hydrosulphuric  acid,  &c.,  the  same  reactions  as  aqueous 
arsenious  acid. 

Nitric  acid  and  aqua  regia  transform  arsenious  into  arsenic 
acid.  Hydrogen,  charcoal,  and  other  reducing  agents  easily 
reduce  it  to  the  metallic  state. 

Arsenious  acid  has  a  rough  taste_,  slightly  metallic,  and 
afterwards  sweetish.  It  is  one  of  the  most  violent  among 
acrid  poisons. 

The  principal  industrial  use  of  arsenious  acid  is  in  cahco- 
printing ;  it  is  also  used  in  glass-making,  serving  to  transform 
the  protoxide  of  iron  into  sesquioxide,  which  produces  glasses 
less  highly  coloured  than  the  protoxide. 

Arsenic  acid,  AsOg,  115  or  1437*5. — This  acid  is  obtained 
by  heating  powdered  arsenious  acid  in  a  basin  with  an  equal 
quantity  of  water,  and  adding  nitric  acid  in  small  quantities 
to  the  mixture  at  the  boiling  point,  so  long  as  ruddy  fumes 
escape.  An  addition  of  hydrochloric  acid  to  the  water  is 
generally  made,  to  increase  the  solubility  of  the  arsenious  acid, 
but  it  is  not  absolutely  necessary.  The  solution  of  arsenic 
acid  is  then  evaporated  to  dryness,  to  expel  the  remaining 
nitric  and  hydrochloric  acids ;  but  the  dry  mass  must  not  be 
heated  above  the  melting  point  of  lead,  otherwise  oxygen  gas 
is  emitted  and  arsenious  acid  reproduced.  Arsenic  acid  thus 
obtained  is  milk-white,  and  contains  no  water.  Exposed  to 
air,  it  slowly  deliquesces,  and  runs  into  a  liquid.  But  notwith- 
standing this,  when  strongly  dried,  it  does  not  dissolve  com- 
pletely in  water  at  once,  and  a  portion  of  it  appears  to  be 
insoluble ;  but  the  whole  is  dissolved  by  continued  digestion. 
Arsenic  acid,  in  absorbing  moisture  from  the  air,  sometimes 
forms  hydrated  crystals,  which  are  highly  deliquescent ;  but 
this  acid  is  easily  made  anhydrous,  and  does  not  retain  basic 
water  with  force,  like  phosphoric  acid.  Its  solution  has  a  sour 
taste,  and  reddens  vegetable  blues.  Arsenic  acid,  indeed,  is  a 
strong  acid,  and  with  the  aid  of  heat  expels  all  the  volatile 

Q3 


208  ARSENIC. 

acids  from  their  combinations.  Arsenic  acid  undergoes  fusion 
at  a  red  heat,  and  at  a  higher  temperature  is  completely  dis- 
sipated in  the  form  of  arsenious  acid  and  oxygen. 

When  an  equivalent  of  arsenic  acid  is  ignited  with  an  excess 
of  carbonate  of  soda,  three  equivalents  of  carbonic  acid  are 
expelled,  and  a  tribasic  arseniate  of  soda  formed,  which  when 
dissolved  in  water,  crystallises  with  24  equivalents  of  water, 
forming  the  salt  3NaO  .  As05H-24HO,  isomorphous  with  the 
subphosphate  of  soda.  The  same  salt  is  obtained  by  treating 
arsenic  acid  in  solution  with  an  excess  of  caustic  soda.  Wlien 
carbonate  of  soda  is  added  to  a  hot  solution  of  arsenic  acid,  so 
long  as  there  is  eflfervescence,  a  salt  is  obtained  by  evaporation 
corresponding  with  the  common  phosphate  of  soda,  containing 
2  eq.  of  soda  and  1  eq.  of  water  as  bases.  This  salt  affects 
the  same  two  multiples,  in  its  water  of  crystallisation,  as 
phosphate  of  soda,  namely,  24HO  and  14H0,  but  most  fre- 
quently assumes  the  smaller  proportion,  forming  the  salt 
2NaO.  HO.  AsOg  +  liHO.  This  arseniate  is  more  soluble 
than  the  phosphate,  and  slightly  deliquescent  in  damp  air. 
When  to  the  last  salt  a  quantity  of  arsenic  acid  is  added  equal 
to  that  which  it  already  contains,  and  the  solution  is  highly 
concentrated,  the  salt  named  biarseniate  of  soda  crystallises 
at  a  low  temperature.  This  salt  contains  1  eq.  of  soda  and 
2  eq.  of  water  as  bases,  with  2  eq,  of  water  of  crystallisation, 
and  corresponds  with  the  biphosphate  of  soda.  Its  formula  is 
Na0.2HO.As05  +  2HO.  The  biarseniate  of  potash,  which  is 
analogous  in  composition,  is  a  highly  crystallisable  salt.  It  is 
sometimes  prepared  by  deflagrating  arsenious  acid  with  an 
equal  weight  of  nitrate  of  potash.  These  arseniates  of  the 
alkalies,  which  contain  water  as  base,  all  lose  that  element  at 
a  red  heat ;  but,  unlike  the  phosphates,  they  recover  it  when 
redissolved  in  water.  Arsenic  acid,  therefore,  fonns  only  one, 
and  that  a  tribasic  class  of  salts.  The  arseniates  of  the  earths 
and  other  metallic  oxides  are  insoluble  in  water,  but  soluble 
in  acids.     Arseniate  of  silver  (3AgO .  AsOg)  falls  as  a  preci- 


SULPHIDES  OF  ARSENIC.  209 

pitate  of  a  chocolate-brown  colour,  when  nitrate  of  silver  is 
added  to  the  solution  of  an  arseniate,  and  affords  an  indication 
of  the  presence  of  arsenic  acid.  On  treating  a  solution  of 
arsenic  acid  with  ammonia  in  excess,  chloride  of  ammonium, 
and  sulphate  of  magnesia,  a  white  crystalline  precipitate  is 
formed,  consisting  of  arseniate  of  magnesia  and  ammonia, 
2MgO  .  NH4O  .  AsOg  +  12  Aq.,  similar  in  appearance  and  ana- 
logous in  constitution  to  the  ammonio-magnesian  phosphate. 
Hydrosulphuric  acid  produces  a  yellow  precipitate  of  AsSg 
after  a  considerable  time ;  but  if  the  solution  be  previously 
mixed  with  sulphurous  acid,  which  reduces  the  arsenic  acid  to 
arsenious  acid,  a  precipitate  of  AsSg  is  immediately  produced. 

Sulphides  of  arsenic.  —  "When  the  bisulphide,  realgar,  is 
digested  in  caustic  potash,  it  gives  off  sulphur  and  leaves  a 
brownish  black  powder,  having  some  resemblance  to  bioxide 
of  lead,  which,  according  to  Berzelius,  is  the  sulphide  AsgS. 
Bisulphide  of  arsenic,  As  85,  is  obtained  by  fusing  sulphur 
with  an  excess  of  arsenic  or  arsenious  acid.  It  is  transparent  and 
of  a  fine  ruby  colour  after  cooling,  and  may  be  distilled  without 
decomposition.  It  forms  the  crystalline  mineral  realgar.  Sulph- 
arsenious  acid,  or  orpiment,  ASS3,  also  occurs  native.  It  may  be 
prepared  by  decomposing  a  solution  of  arsenious  acid  in  hydro- 
chloric acid,  by  hydrosulphuric  acid  or  by  an  alkaline  sulphide. 
This  sulphide  has  a  rich  yellow  colour,  and  is  the  basis  of  the 
pigment  called  hinges  yellow.  It  is  insoluble  in  acids,  but 
soluble  to  a  small  extent  in  water  containing  hydrosulphuric 
acid,  and  also  in  pure  water,  but  is  precipitated  by  ebullition 
with  a  little  hydrochloric  acid.  When  heated,  it  fuses  readily 
and  becomes  crystalline  on  cooling.  It  is  readily  dissolved 
by  ammonia  and  solutions  of  the  fixed  alkalies,  and  is  indeed 
a  powerful  sulphur-acid.  Sulpharsenic  acid,  AsSg,  falls  as  a 
yellow  precipitate,  having  much  the  appearance  of  orjnment, 
when  a  solution  of  arsenic  acid  somewhat  concentrated  is 
decomposed  by  hydrosulphuric  acid.     It   may  be  sublimed 

Q  4 


210  ARSENIC. 

without  change,  and  after  cooling  forms  a  non- crystalline 
mass.  It  is  also  a  powerful  sulphur-acid,  forming  salts  called 
sulpharseniates.  Persulphide  of  arsenic ,  AsSjg,  is  obtained  by 
precipitating  neutral  solution  of  sulpharseniate  of  potassium 
with  alcohol,  filtering  the  liquid,  and  evaporating  off  two- 
thirds  of  the  alcohol;  the  concentrated  solution,  when  left 
to  cool,  deposits  the  persulphide  of  arsenic  in  shining  yellow 
crystalline  laminae. 

Chlorides  of  arsenic. — A  tercMoride,  As  CI3,  corresponding 
with  arsenious  acid,  is  formed  when  arsenic  is  introduced  into 
chlorine  gas,  in  which  it  takes  fire  and  bums  spontaneously. 
The  same  compound  is  obtained  by  distilling  a  mixture  of 
1  part  of  arsenic  with  6  parts  of  corrosive  sublimate ;  also  by 
distilling  arsenious  acid  with  excess  of  hydrochloric  acid,  or  of 
common  salt  and  sulphuric  acid.  It  is  a  colourless,  oily, 
and  very  dense  liquid,  which  is  resolved  by  water  into  arse- 
nious and  hydrochloric  acids.  When  a  mixture  of  arsenic  and 
calomel  is  distilled,  a  dark  brown  sublimate  is  formed,  consist- 
ing partly  of  Hg2ClAs,  partly  of  Hg4ClAs.  No  chloride  cor- 
responding with  arsenic  acid  is  known.  Bromide  of  arsenic y 
AsBrg,  is  formed  by  the  direct  combination  of  its  elements. 
Iodide  of  arsenic.  As  I3,  is  formed,  according  to  Plisson,  by 
digesting  3  parts  of  arsenic  with  10  of  iodine  and  100  of 
water,  as  long  as  the  odour  of  iodine  is  perceived.  The 
liquid  yields  by  evaporation  red  crystals  of  the  iodide.  Fluo- 
ride of  arsenic,  AsFg,  is  obtained  by  distilling  a  mixture  of 
fluor  spar  and  arsenious  acid  with  sulphuric  acid.  It  is  a 
fuming,  colourless  liquid ;  the  density  of  its  vapour  is  2730 
(Unverdorben). 

Arsenic  and  hydrogen. —  A  solid  arsenide  of  hydrogen  was 
obtained  by  Davy,  by  using  metallic  arsenic  as  the  negative 
pole  (the  chloroid)  in  decomposing  water.  Gay-Lussac  and 
Thenard  have  also  shown  that  the  same  compound  precipitates 
when  arsenide  of  potassium  is  dissolved  in  water.  It  is  a 
chestnut-brown  powder,  which  may  be  dried  without  change. 


TESTING    FOR    ARSENIC.  211 

Its  composition  has  not  been  determined  with  accuracy. 
Arseniuretted  hydrogen,  AsHg,  a  gas  analogous  in  constitu- 
tion to  ammonia,  is  obtained  by  dissolving  arseniate  of  potas- 
sium or  sodium  in  water,  or  an  alloy  of  equal  parts  of  zinc 
and  arsenic  in  sulphuric  acid  diluted  with  three  times  its 
weight  of  water;  or  again,  when  zinc  dissolves  in  hydro- 
chloric or  dilute  sulphuric  acid,  with  which  arsenious  acid  is 
mixed  : 

6Zn  -h  3H0  +  AsOg  +  6SO3  =  6(ZnO  .  SO3)  +  AsHg. 

It  is  a  dangerous  poison,  when  inhaled  even  in  the  most 
minute  quantity,  and  should,  therefore,  be  prepared  with  the 
greatest  caution.  The  density  of  this  gas  is  2695  (Dumas). 
It  is  liquefied  by  a  cold  of  — 40°.  When  passed  through  a 
glass  tube  heated  to  redness  by  a  spirit  lamp,  it  is  decom- 
posed and  deposits  metallic  arsenic.  The  flame  of  this  gas, 
when  burned  in  air,  also  deposits  metallic  arsenic  upon  a 
cold  object  exposed  to  it.  No  combination  of  arseniuretted 
hydrogen  is  known  with  either  acids  or  bases.  It  precipitates 
many  of  the  metallic  solutions  which  are  precipitated  by  hy- 
drosulphuric  acid,  but  not  oxide  of  lead,  its  hydrogen  alone 
being  oxidated,  and  the  arsenic  being  precipitated  in  com- 
bination with  the  metal.  From  the  salts  of  silver,  gold, 
platinum,  and  rhadium,  it  precipitates  the  metals,  while  arse- 
nious acid  remains  in  solution.  This  gas,  when  pure,  is 
completely  absorbed  by  a  solution  of  sulphate  of  copper,  and 
AsCug  precipitated. 

TESTING   FOR   ARSENIC. 

Poisoning  from  arsenious  acid  is  much  more  frequent  than 
from  any  other  substance.  Hence,  a  more  than  usual  degree 
of  importance  is  attached  to  the  modes  of  detecting  the  pre- 
sence of  arsenic  in  minute  quantity.  Of  the  diflPerent  prepa- 
rations of  the  metal,  arsenic  acid,  and  after  it  arsenious  acid. 


212  ARSENIC. 

are  the  most  poisonous ;  the  salts  and  sulphides  are  so  in  a 
much  less  degree.  Arsenious  acid  in  the  solid  form  and  un- 
mixed with  foreign  matters,  is  easily  recognised  as  a  white 
heavy  powder,  which  is  tasteless  or  nearly  so,  is  entirely 
volatilised  by  heat,  and  diffuses  a  garlic  odour  in  the  re- 
ducing flame  of  a  lamp.  When  dissolved  in  water,  arsenious 
acid  may  be  detected  by  the  fluid  tests,  already  mentioned 
(pp.  205,  206.).  The  silver  and  copper  tests  are  most  con- 
veniently applied  in  the  following  forms. 

1.  Ammonio-niirate  of  silver. — This  is  an  exceedingly  deli- 
cate test  of  arsenious  acid,  whether  free,  or  in  combination 
with  an  alkali.  It  is  prepared  by  adding  diluted  ammonia 
to  a  solution  of  nitrate  of  silver,  till  the  oxide  of  silver,  which 
is  first  thrown  down,  is  redissolved.  When  the  ammonia 
has  been  added  in  proper  quantity  and  not  in  excess,  the  odour 
of  that  substance  is  scarcely  perceptible,  and  the  liquid  con- 
tains in  solution  the  crystallisable  ammonio-nitrate  of  silver, 
AgO.NOg  .  2NH3.  This  test-liquid  throws  down  from  arse- 
nious acid,  the  yellow  arsenite  of  silver,  which  is  redissolved 
both  by  acids  and  by  ammonia.  A  solution  of  nitrate  of  silver, 
gives  the  same  indication  as  the  prepared  ammonio-nitrate 
in  an  alkaline  but  not  in  an  acid  solution  of  arsenious  acid. 
Nitrate  of  silver  produces,  in  phosphate  of  soda  or  any  other 
soluble  phosphate,  a  yellow  precipitate  of  phosphate  of  silver 
of  the  same  colour  as  the  arsenite  of  silver,  and  which  might, 
therefore,  be  mistaken  for  the  latter;  but  the  action  of  the 
ammonio-nitrate  is  not  liable  to  tliat  ambiguity,  as  it  does  not 
produce  a  yellow  precipitate  in  an  alkaline  solution  of  phos- 
phoric acid,  the  phosphate  of  silver  being  then  retained  in  so- 
lution by  the  ammonia  of  the  reagent,  although  arsenite  of 
silver  is  precipitated  in  the  same  circumstances.  Both  phos- 
phate and  arseniate  of  silver  are  indeed  considerably  more 
soluble  in  ammonia  than  the  arsenite  of  the  same  metal. 

2.  Ammonio -sulphate  of  copper  gives  a  beautiful  green  pre- 
cipitate, the  arsenite  of  copper,  in  both  alkaline  and  acid  solu- 


TESTING    FOR   ARSENIC.  213 

tions  of  arsenious  acid;  sulphate  of  copper  gives  the  same 
precipitate  in  the  former,  but  not  in  the  latter. 

But  in  solutions  containing  organic  matter,  the  indications 
of  these  tests  are  sometimes  delusive,  and  often  doubtful. 
Eecourse  is  then  had  to  the  proper  means  of  obtaining 
arsenic  in  the  metallic  form,  from  the  liquid  suspected 
to  contain  arsenious  acid.  Indeed,  even  where  the  indica- 
tions of  the  fluid  tests  are  clear,  the  reduction  test  should 
never  be  omitted,  the  evidence  which  it  affords  being  of 
a  superior  and  completely  demonstrative  character.  The 
reduction  test  of  arsenic  is  practised  in  two  different  ways : 
(1.)  by  the  reduction  of  the  sulphide  of  arsenic  by  means  of 
charcoal  and  carbonate  of  potash,  and  (2.)  by  the  production, 
and  subsequent  decomposition  of  the  gaseous  compound  of 
arsenic  and  hydrogen.  The  following  operations  are  neces- 
sary in  the  practice  of  the  first  method  : — 


REDUCTION    TEST    OF   ARSENIC. 

I.  Preparation  of  the  fluid  : 

1.  Heat  the  mass  with  about  one-fourth  of  its  weight 
of  strong  sulphuric  acid  in  a  retort,  to  which  is 
adapted  a  receiver  having  its  inner  surface  wetted, 
till  the  organic  matter  is  carbonised. 

2.  Pulverise  the  residue,  and  treat  it  with  nitric  acid 
mixed  with  a  little  hydrochloric  acid,  in  order  to 
bring  the  arsenic  to  the  state  of  arsenic  acid,  which 
is  easily  soluble. 

3.  Boil  with  water ;  filter ;  and  mix  the  filtrate  with 
the  liquid  in  the  receiver.* 

*  This  is  the  mode  of  preparation  most  generally  adopted,  and  it  is  appli- 
cable to  all  cases  of  searching  for  mineral  poisons.  Another  method,  which  is 
especially  applicable  when  the  matter  to  be  examined  contains  a  large  quan- 
tity of  fat,  is  to  heat  the  mass  with  strong  hydrochloric  acid,  or  aqua-regia,  in 


214  ARSENIC. 

IT.  Precipitation  of  the  sulphide  of  arsenic  : 

1.  Transmit  a  stream  of  hydrosulphuric  acid  gas 
through  the  liquid  for  half  an  hour.* 

2.  Heat  the  liquid  in  an  open  vessel  for  a  few  minutes, 
to  cause  the  precipitate  to  separate. 

3.  Wash  the  precipitate  by  aflPusion  of  water  acidulated 
with  hydrochloric  acid,  and  subsidence. 

4.  Dry  the  precipitate  at  a  temperature  not  exceeding 
300°. 

III.  Reduction  of  the  sulphide  of  arsenic : 

1.  Mix  the  dried  precipitate  intimately  with  twice  its 
bulk  of  dry  black  flux  (carbonate  of  potash  and 
charcoal),  or  with  a  mixture  of  pounded  charcoal 
and  dry  carbonate  of  soda,  or  with  cyanide  of 
potassium,  and  heat  to  redness  in  a  glass  tube,  of 
the  form  and  size  of  a  or  b,  exhibited  below. 

2.  Heat  slowly  a  particle  of  the  metallic  crust  in  a 
glass  tube  c,  and  observe  the  formation  of  a  white 
crystalline  sublimate  of  arsenious  acid. 

3.  Dissolve  the  sublimate  in  a  small  quantity  of  boiling 
water,  and  test  with  ammonio-nitrate  of  silver,  &c., 
as  above. 

Fig.  8. 

(  ' 


O 


C 


a  large  retort ;  the  greater  part  of  the  arsenic  is  then  converted  into  chloride, 
and  may  be  collected  in  a  receiver  containing  water. 

*  As  the  arsenic  is  in  the  state  of  arsenic  acid,  it  is  best  to  mix  the  liquid 
with  sulphurous  acid  before  passing  the  hydrosulphuric  acid  gas  through  it. 


TESTING    FOR   ARSENIC. 


215 


Fig.  9. 


Marshes  test, — Hydrogen  cannot  be  evolved  in  contact  with 
any  preparation  of  arsenic,  soluble  or  insoluble,  without  com- 
bining with  the  metal,  which  is  thus  removed  from  the  liquor, 
in  the  form  of  arseniuretted  hydrogen  gas.     Mr.  Marsh  has 
founded,  upon  this  fact,  a  simple  and  elegant  mode  of  obtain- 
ing metallic  arsenic  from  arsenical  liquors.     The   stopcock 
being  removed  from  the  bulb-apparatus  re- 
presented in  the  figure,  a  fragment  of  zinc 
is  placed  in  the  lower  bulb,  and  diluted  sul- 
phuric acid  poured  upon  it.     The  stopcock 
being  replaced  and  closed,  the  lower  bulb  is 
soon  filled  with  hydrogen  gas,  and  the  acid 
liquid  forced  into  the  upper  bulb.     It  is  ne- 
cessary to  test  this  hydrogen  for   arsenic, 
which  will  be  found  in  it,  if  the  zinc  itself 
contains  that  metal.     The  gas  for  this  pur- 
pose is  kindled  at  the  stopcock  and  allowed 
to  burn  with  a  small  flame.     If  a  stoneware 
plate  be  depressed  upon  the  flame,  a  black 
spot   of  a  steel- grey   colour  and  bright  metallic   lustre,   is 
formed,  in  a  few  seconds,  upon  the  surface  of  the  plate,  sup- 
posing the  gas  to  contain  arsenic ;  or  if  a  cold  piece  of  glass 
be  held  over  the  flame,  at  a  smaU  height  above  it,  a  white 
sublimate  of  arsenious  acid  condenses  upon  the  glass.     But  if 
the  zinc  employed  contains  no  arsenic,  neither  of  these  eflPects 
is  produced.     The  zinc  being  proved  to  be  free  from  arsenic, 
a  portion  of  the  liquor  to  be  tested  is  introduced  into  the 
lower  bulb,  in  addition  to  the  acid  and  zinc  already  there ; 
and  when  the  bulb  is  again  filled  with  hydrogen  gas,  the 
latter  is  burned  and  examined  precisely  as  before.     If  the 
liquor  is  loaded  with  organic  matter,  as  generally  happens 
with  the  liquids  submitted  to  examination  in  actual  cases  of 
poisoning,  the  gas  may  be  filled  with  froth,  and  the  evolution 
of  it  very  slow.     But  in  the  course  of  a  night,  the  gas  is 


216  ARSENIC. 

generally  obtained  in  suflBcient  quantity,  and  in  a  proper 
state,  to  permit  of  examination.  It  is  much  better,  however, 
first  to  remove  the  organic  matter  by  one  of  the  methods 
above  given;  the  gas  is  then  evolved  freely  and  without 
frothing,  and  a  plain  bottle  with  a  cork  and  glass  jet  will  be 
sufficient  for  this  reduction  experiment.  Then  also,  instead 
of  burning  the  gas  at  the  jet,  it  may  be  allowed  to  escape  by 
a  horizontal  tube,  such  as  that  in  figure  10.,  a  portion  of 

which  is  heated  to  redness  by 
^S'  10.  a    spirit    lamp.     The   arsenic 

/^  I  condenses  within  the  tube,  be- 

yond the  flame  and  nearer  the 
'jl     Tp  aperture,  and  forms  a  metallic 

crust,  which  may  be  converted 
by  sublimation  into  arsenious 
acid;  the  sublimate  may  then 
be  dissolved  in  a  small  quan- 
tity of  boiling  water,  and  the 
solution  tested  with  ammonio- 
nitrate  of  silver,  &c.,  as  before. 
Wlien  the  liquid  examined  contains  antimony,  that  metal 
combines  with  the  nascent  hydrogen,  and  comes  off  as  anti- 
moniuretted  hydrogen,  a  gas  which,  when  burned,  or  heated 
in  a  glass  tube,  gives  the  metal  and  a  white  sublimate,  in  the 
same  circumstances  as  arsenic  (L.  Thompson).  Antimony, 
however,  may  be  recognised  by  a  peciUiarity  of  its  reduction 
in  the  ignited  tube.  This  metal  is  deposited  in  the  tube,  on 
both  sides  of  the  heated  portion  of  it,  and  closer  to  the  flame 
than  arsenic,  owing  to  the  inferior  volatility  of  antimony.  The 
white  sublimate  also,  if  dissolved  in  water  containing  a  drop 
of  ammonia,  will  not  give  the  proper  indications  with  the 
fluid  tests  of  arsenic,  if  the  metal  be  antimony.  Another  dis- 
tinction is,  that  the  arsenical  deposit  is  soluble  in  hypochlorite 
of  soda,  whereas  the  antimonial  deposit  is  not. 


ESTIMATION    OF   ARSENIC.  217 

Antidotes  to  arsenious  acid, — When  hydrated  sesquioxide 
of  iron  is  mixed  with  a  solution  of  arsenious  acid  to  the  con- 
sistence of  a  thin  paste,  a  reaction  occurs  by  which  the  ar- 
senious acid  disappears  in  a  few  minutes,  and  the  mass  ceases 
to  be  poisonous.  The  arsenious  acid  takes  oxygen  from  the 
sesquioxide  of  iron,  and  becomes  arsenic  acid,  while  the 
sesquioxide  of  iron  is  reduced  to  protoxide,  a  protarseniate  of 
iron  being  the  result,  which  is  insoluble  and  inert : 

SFcaOa  +  AsOg  =  4FeO  .  AsOg. 

The  constitution  of  this  arseniate  of  iron  is  probably 
2FeO.HO.AsO5 +  2FeO.  Sesquioxide  of  iron,  when  used 
as  an  antidote  to  arsenious  acid,  should  be  in  a  gelatinous 
state,  as  it  is  obtained  by  precipitation,  without  drying.  It 
may  be  prepared  extemporaneously,  by  adding  bicarbonate  of 
soda  in  excess  to  any  tincture  or  red  solution  of  iron.  Cal- 
cined magnesia  may  likewise  be  used  as  an  antidote  to 
arsenic.  Care  should  be  taken  in  preparing  the  latter  not  to 
employ  too  great  a  heat,  which  would  render  it  very  dense, 
and  cause  it  to  combine  but  slowly  with  the  arsenious  acid. 


ESTIMATION    OF   AKSENIC,    AND    METHODS    OF    SEPARATING    IT 
FROM    THE    PRECEDING    METALS. 

When  arsenic  is  contained  in  a  solution  entirely  in  the 
form  of  arsenic  acid,  the  best  mode  of  estimating  it  is  to  pre- 
cipitate it  in  the  form  of  ammonio-magnesian  arseniate, 
2MgO  .  NH4O  .  ASO5  + 12H0.  The  solution  is  mixed  with 
excess  of  ammonia,  and  then  with  sulphate  of  magnesia,  to 
which  a  quantity  of  chloride  of  ammonium  has  been  added, 
sufficient  to  prevent  the  precipitation  of  the  magnesia  by  am- 
monia.    The  liquid  is  then  left  to  stand  for  about  twelve 


218  ARSENIC. 

hours ;  the  precipitate  collected  on  a  weighed  filter ;  washed 
with  water  containing  ammonia ;  and  dried  over  sulphuric 
acid  in  vacuo  at  ordinary  temperatures ;  it  has  then  the  com- 
position expressed  by  the  above  formula.  It  may  also  be 
dried,  and  more  expeditiously,  by  exposing  it  to  a  temperature 
of  exactly  212°  F.,  whereby  it  loses  11  eq.  of  water,  and  is 
reduced  to  2MgO.NH40.As05  +  HO.  Exposure  to  a  higher 
temperature  occasions  loss  of  arsenic. 

If  the  liquid  contains  arsenious  acid,  that  compound  may 
be  converted  into  arsenic  acid  by  mixing  the  solution  with 
hydrochloric  acid,  and  adding  chlorate  of  potash  by  small 
quantities.  The  vessel  must  be  left  in  a  moderately  warm 
place  till  the  odour  of  free  chlorine  has  entirely  disappeared. 
Aqua  regia  may  also  be  used  to  effect  the  oxidation,  but  it  is 
less  convenient.  In  either  case,  the  liquid  must  be  consider- 
ably diluted  with  water,  otherwise  part  of  the  arsenic  will  be 
converted  into  chloride,  and  volatilised.  It  is  best,  perhaps, 
to  perform  the  oxidation  in  a  capacious  retort  having  a 
receiver  adapted  to  it. 

Arsenious  acid  may  also  be  estimated  by  its  action  on 
terchloride  of  gold.  The  arsenious  acid  is  thereby  converted 
into  arsenic  acid,  and  gold  is  precipitated  in  the  metallic 
state.  The  quantity  of  gold  thus  reduced  gives  the  quantity 
of  arsenious  acid  present : 

2  AUCI3  +  6110  +  3  ASO3  =  2  Au  +  6HC1  -f  SAsOg. 

The  gold  solution  used  for  the  purpose  is  the  sodio-chloridc, 
or  ammonio-chloride  of  gold.  It  must  be  free  from  nitric 
acid ;  but  the  presence  of  hydrochloric  acid,  even  in  large 
excess,  does  not  interfere  with  the  action.  The  liquid,  after 
the  addition  of  the  arsenic  solution,  must  be  left  to  itself 
for  a  considerable  time  to  enable  the  gold  to  settle  down 
completely. 

When  arsenic  and  arsenious  acids  exist  together  in  solution 


SEPARATION    OP   ARSENIC.  219 

the  former  may  be  precipitated  as  ammonio-magnesian 
arseniate  (a  considerable  quantity  of  sal-ammoniac  being 
added  to  prevent  the  simultaneous  precipitation  of  the  ar- 
senious  acid);  the  arsenious  acid  converted  into  arsenic  acid 
by  oxidation  with  chlorate  of  potash  and  hydrochloric  acid, 
and  then  precipitated  in  a  similar  manner ;  or  the  arsenious 
acid  may  be  estimated  by  chloride  of  gold,  as  last  described. 

The  separation  of  arsenic  in  solution  from  the  alkalies, 
earths,  and  those  metals  which  are  not  precipitated  from  their 
acid  solutions  by  hydrosulphuric  acid,  is  effected  by  passing  a 
stream  of  that  gas  through  the  acid  liquid  for  a  considerable 
time,  then  leaving  it  to  stand,  and  heating  it  gently  to 
ensure  the  complete  precipitation  of  the  sulphide  of  arsenic. 
If  the  arsenic  is  in  the  form  of  arsenic  acid,  that  compound 
must  be  previously  reduced  to  arsenious  acid  by  means  of 
sulphurous  acid.  The  tersulphide  of  arsenic  is  collected  on  a 
weighed  filter,  thoroughly  washed,  and  dried  at  a  moderate 
heat.  If  quite  pure,  it  may  be  weighed  with  the  filter,  and 
the  quantity  of  arsenic  thereby  directly  determined.  But  as 
it  almost  always  contains  an  excess  of  sulphur,  it  is  better  to 
take  a  weighed  quantity  of  it  from  the  filter,  oxidise  it  in  a 
capacious  flask  by  means  of  dilute  hydrochloric  acid  and 
chlorate  of  potash,  continuing  the  operation  till  the  greater 
part  of  the  sulphur  is  converted  into  sulphuric  acid,  and  the 
remainder  collects  at  the  bottom  of  the  liquid  in  a  compact 
yellow  globule ;  then  decant  the  liquid,  wash  the  globule  of 
sulphur,  and  weigh  it ;  and,  finally,  estimate  the  quantity  of 
sulphur  in  the  solution  by  precipitation  with  chloride  of 
barium,  adding  the  quantity  thus  found  to  the  weight  of  the 
globule.  The  proportion  of  sulphur  in  the  precipitated  sul- 
phide of  arsenic  being  thus  ascertained,  the  amount  of  arsenic 
is  easily  calculated. 

From  cadmium,  copper,  and  lead,  arsenic  may  be  separated 
by  means  of  sulphide  of  ammonium.  The  filtered  ammoniacal 
solution  is  then  treated  with  excess  of  hydrochloric  or  acetic 

VOL.  II.  R 


220  ARSENIC. 

acid  to  throw  down  the  sulphide  of  arsenic,  and  the  precipi- 
tate treated  in  the  manner  just  described. 

The  separation  of  arsenic  from  tin  is  attended  with  con- 
siderable difficulty.  One  of  the  best  methods  is  to  convert 
the  two  metals  into  sulphides,  and  separate  them,  after  drying 
and  weighing  the  whole,  by  ignition  in  a  stream  of  hydro- 
sulphuric  acid  gas.  The  mixed  sulphides  are  introduced 
into  a  weighed  glass  bulb,  having  a  tube  attached  to  it  on 
each  side.  One  of  these  tubes,  the  exit-tube,  must  be  at 
least  a  quarter  of  an  inch  in  diameter,  to  prevent  stoppage, 
and  bent  downwards  so  as  to  dip  into  a  flask  containing  am- 
monia. The  whole  is  then  weighed,  hydi-osidphuric  acid 
gas  passed  through  the  apparatus,  and  the  bidb  heated  till 
the  whole  of  the  sulphide  of  arsenic  is  sublimed.  Part  of  the 
sulphide  of  arsenic  passes  into  the  ammoniacal  liquid,  by 
which  it  is  dissolved,  and  the  rest  sublimes  in  the  wide  tube. 
When  the  operation  is  ended,  and  the  apparatus  has  cooled, 
the  wide  tube  is  cut  off  at  a  short  distance  from  the  bulb, 
then  broken,  and  the  pieces  digested  in  caustic  potash  to 
dissolve  out  the  sulphide  of  arsenic.  The  solution  thus  ob- 
tained is  added  to  the  ammoniacal  liquid  in  the  flask ;  the 
sulphide  of  arsenic  precipitated  by  hydrochloric  acid,  oxidised 
without  previous  filtration  with  hydrochloric  acid  and  chlo- 
rate of  potash  ;  and  the  resulting  arsenic  acid  precipitated  by 
ammonia  and  sulphate  of  magnesia.  The  sulphide  of  tin 
remaining  in  the  bulb  is  converted  into  stannic  oxide  by 
treating  it  with  strong  nitric  acid. 

When  arsenic  is  combined  with  other  metals  in  the  form 
of  an  alloy,  the  whole  may  be  dissolved  or  oxidised  by  means 
of  aqua  regia,  or,  better,  with  hydrochloric  acid  and  chlorate 
of  potash,  and  the  arsenic  separated  by  one  of  the  preceding 
methods.  In  the  case  of  tin,  however,  it  is  best  to  fuse  the 
alloy  in  thin  laminae  with  five  times  its  weight  of  carbonate  of 
soda  and  an  equal  quantity  of  sulphur,  whereby  a  mixture  of 
sulpharseniate  and  sulphostannate  of  soda  is  obtained,  which 


ANTIMONY.  221 

dissolves  completely  in  hot  water.  The  sulphides  of  tin  and 
arsenic  may  then  be  precipitated  by  hydrochloric  acid,  and 
separated  as  above.* 


SECTION    II. 

ANTIMONY. 

Eq.  120-24  or  1503t;    Sb  {stibium). 

This  metal  was  well  known  to  the  alchemists,  and  is  one 
of  the  metals  the  preparations  of  which  were  first  introduced 
into  medicine.  Its  sulphide  is  not  an  uncommon  mineral, 
and  is  the  source  from  which  the  metal  and  its  compounds 
are  always  derived. 

The  sulphide  of  antimony  is  easily  reduced  to  the  metallic 
state  by  mixing  together  4  parts  of  that  substance,  3  parts  of 
crude  tartar,  and  \\  parts  of  nitre,  and  projecting  the  mixture 
by  small  quantities  at  a  time  into  a  red  hot  crucible.  The 
sulphide  is  also  sometimes  reduced  by  fusion  with  small  iron 
nails,  which  combine  with  the  sulphur  and  disengage  the 
antimony.  Or  it  may  be  obtained  in  a  state  of  greater  purity 
by  strongly  igniting  in  a  crucible  a  quantity  of  the  potash- 
tartrate  of  antimony,  and  placing  the  resulting  metallic  mass 
in  water  to  remove  any  potassium  it  may  have  acquired. 

Antimony  is  a  white  and  brilliant  metal,  generally  pos- 
sessing a  highly  lamellated  structure.     It  is  easily  obtained 

*  For  a  full  account  of  the  methods  of  estimating  arsenic  and  separating 
it  from  other  metals,  vide  H.  Rose,  *'  Ilandbuch  der  analytischen  Chemie," 
1851,  ii.  381. 

t  The  number  129,  given  by  Berzelius  for  the  equivalent  of  antimony,  and 
hitherto  generally  adopted,  appears  from  recent  experiments  by  Schneider 
(Pogg.  Ann.  xcviii.  293)  and  by  H.  Rose  (Berl.  Akad.  Ber.  1856,  p.  229) 
to  be  much  too  high.  Schneider,  by  reducing  the  tersulphide  of  antimony 
with  hydrogen,  finds  the  equivalent  to  be  120'24  ;  and  Rose,  by  decomposing 
the  terchloride  with  hydrosulphuric  acid,  and  precipitating  tlie  chlorine  with 
nitrate  of  silver,  finds  the  number  120-69. 

B  2 


222  ANTIMONY. 

in  rhombohedral  crystals  of  the  same  form  as  arsenic  and 
tellurium.  Its  density  is  from  6*702  to  6-86.  It  under- 
goes no  change  in  the  air.  The  point  of  fusion  of  antimony 
is  estimated  at  797°;  it  may  be  distilled  at  a  Avhite  heat. 
This  metal  bums  in  air  at  a  red  heat,  and  produces  copious 
fumes  of  oxide  of  antimony. 

Antimony  combines  in  three  proportions  with  oxygen,  form- 
ing oxide  of  antimony  and  antimonic  acid,  SbOg  and  SbOg, 
which  correspond  respectively  with  arsenious  and  arsenic  acids ; 
and  antimonious  acid,  Sb04,  which  is  probably  an  intermediate 
or  compound  oxide,  analogous  to  the  black  oxide  of  iron. 

Teroxide  of  antimony,  Antimonic  oxide,  Antimonious  acid, 
SbOg,  144-24  or  1803.— This  oxide  may  be  obtained  by  dis- 
solving the  sulphide,  finely  pounded  and  in  the  condition  in 
which  it  is  known  as  prepared  sulphide  of  antimony,  in  four 
times  its  weight  of  concentrated  hydrochloric  acid.  Pure 
hydrosulplmric  acid  goes  oflP,  and  the  antimony  is  converted 
into  terchloride  : 

SbSg  +  3HC1  =  SbClg  +  3HS. 

The  clear  solution  may  be  poured  off,  and  precipitated  at 
the  boiling  heat  by  a  solution  of  carbonate  of  potash  added 
in  excess,  the  carbonic  acid,  which  does  not  combine  with 
oxide  of  antimony,  escaping  as  gas.  Teroxide  of  antimony, 
so  prepared,  is  anhydrous,  but  is  slightly  soluble  in  water: 
it  is  white,  but  assumes  a  yellow  tint  when  heated.  It  is 
fusible  at  a  red  heat,  and  sublimes  at  a  high  temperature 
in  a  close  vessel,  where  it  cannot  pass  into  a  higher  state  of 
oxidation.  The  brilliant  crystalline  needles  which  condense 
about  antimony  in  a  state  of  combustion  likewise  consist  of 
this  oxide.  They  possess  the  unusual  prismatic  form  of  ar- 
senious acid  observed  by  Wohler.  Oxide  of  antimony  also 
crystallises  as  frequently  in  regular  octohedrons,  the  other 
form  of  arsenious  acid.  It  occurs  in  the  prismatic  form  as  a 
rare  mineral,  whose  density  is  5 '227. 


SALTS    OF   ANTIMONY.  223 

When  a  solution  of  potash  is  poured  upon  the  bulky  hydrate 
of  teroxide  of  antimony,  which  is  precipitated  from  the  chloride 
by  water,  a  portion  of  the  oxide  is  dissolved,  but  the  greater 
part  loses  its  water,  and  is  reduced  in  a  few  seconds  to  a  fine 
greyish,  crystalline  powder,  which  is  a  neutral  combination  of 
teroxide  of  antimony  with  potash.  Teroxide  of  antimony  also 
combines  with  acids,  forming  the  salts  of  antimony y  or  an- 
timonic  salts. 

The  solutions  of  these  salts  giv^e  with  hydrosulphuric  acid 
a  brick-red  precipitate  of  tersulphide  of  antimony,  easily 
soluble  in  sulphide  of  ammonium,  and  reprecipitated  by  acids. 
This  precipitate  dissolves  in  strong  boiling  hydrochloric  acid, 
forming  the  terchloride,  which  when  thrown  into  water  yields 
a  precipitate  of  the  oxychloride.  This  reaction  with  hydro- 
sulphuric  acid  distinguishes  antimony  from  all  other  metals.* 
Zinc  or  iron  precipitates  antimony  from  its  solutions  in  the 
form  of  a  black  powder,  which,  when  fased  on  charcoal  before 
the  blow-pipe,  yields  a  brittle  button  of  the  metal.  According 
to  Dr.  Odlingtj  antimony  is  also  precipitated  by  copper,  in  the 
form  of  a  brilliant  metallic  film,  which  may  be  dissolved  ofi* 
the  copper  by  a  solution  of  permanganate  of  potash,  yielding 
a  solution  which  will  give  the  characteristic  red  precipitate 
with  hydrosulphuric  acid.  This  reaction  affords  a  ready 
method  of  separating  antimony  from  liquids  containing 
organic  matter, — as  in  medico-legal  inquiries.  All  compounds 
of  antimony  fused  upon  charcoal  with  carbonate  of  soda  or 
cyanide  of  potassium,  yield  a  brittle  globule  of  antimony,  a 
thick  white  fume  being  at  the  same  time  given  off,  and  the 
charcoal  covered  to  some  distance  around  with  a  white  de- 
posit of  antimonic  oxide.  The  reduction  with  cyanide  of 
potassium  may  also  be  performed  in  a  porcelain  crucible, 
without  charcoal.     A  solution  of  terchloride  of  gold  added  to 

*  For  the  reactions  of  antimonic  salts  witli  alkalies,  see  terchloride  of  aniU 
movy  and  tartar-emetic. 

t  Guj's  Hospital  Reports,  [3.]  ii.  249. 

B  3 


324  ANTIMONY. 

the  solution  of  a  salt  of  teroxide  of  antimony,  forms  a  yellow 
precipitate  of  metallic  gold,  tlie  oxide  of  antimony  being  at 
the  same  time  converted  into  antimonic  acid,  which  com- 
pound is  precipitated  as  a  white  powder,  together  with  the 
gold,  unless  the  solution  contains  a  very  large  excess  of  hydro- 
chloric acid.  In  a  solution  of  oxide  of  antimony  in  potash, 
terchloride  of  gold  produces  a  Mack  precipitate,  which  is  not 
altered  by  heating.     This  reaction  is  extremely  delicate. 

Tersulphide  of  antimony ,  SbSg,  168-24  or  2103. — The  com- 
mon ore  of  antimony  is  a  tersulphide,  SbSg,  corresponding  with 
the  preceding  oxide  of  antimony.  It  is  rarely  free  from  sul- 
phide of  arsenic,  which  thus  often  enters  into  the  antimonial 
preparations  derived  from  the  sulphide  of  antimony,  but  into 
tartar-emetic  less  frequently  than  the  others.  The  same 
sulphide  is  formed  when  salts  of  the  oxide  of  antimony,  such 
as  tartar- emetic,  are  precipitated  by  hydrosulphuric  acid;  but 
it  is  then  of  an  orange-red  colour.  When  the  precipitated 
sulphide  is  dried,  it  loses  water  and  becomes  anhydrous,  still 
remaining  of  a  dull  orange  colour ;  but  when  heated  more 
strongly,  it  shrinks  at  a  particular  temperature,  and  assumes 
the  black  colour  and  metallic  lustre  of  the  native  sulphide. 
This  sulphide  is  also  obtained  of  a  dark  brown  colom*  by 
boiling  the  prepared  sulphide  of  antimony  in  a  solution  of 
carbonate  of  potash,  and  allowing  the  solution  to  cool;  by 
fusing  2}  parts  of  the  prepared  sulphide  with  1  part  of  car- 
bonate of  potash;  or  dissolving  it  in  a  boiling  solution  of 
caustic  potash,  and  afterwards  adding  an  acid.  The  last  pre- 
paration is  known  as  Kermes  mineral.  It  has  a  much  duller 
colour  than  the  precipitated  sulphide,  but  differs  from  it 
only  in  containing  small  quantities  of  oxide  and  pentasulphide 
of  antimony,  together  with  an  alkaline  sulphide  which  can- 
not be  removed  by  washing  (Berzelius).  When  the  cooled 
mother-liquor  from  which  kermes  is  deposited  is  mixed  with 
hydrochloric  acid,  a  precipitate  is  obtained,  consisting,  like  the 
kermes,  of  SbS3  mixed  with  SbOa  and  SbSg,  but  of  a  redder 


I 
TERCHLORIDE  OF  ANTIMONY.  226 

colour.  It  is  sometimes  called  the  golden  sulphwret  of 
antimony. 

When  the  sulphide  of  antimony  is  oxidated  at  a  red  heat, 
much  sulphur  is  burned  off,  and  an  impure  oxide  of  antimony 
remains.  This  matter  forms,  when  fused,  the  glass  of  anti- 
mony,which  contains  a  considerable  quantity  of  undecomposed 
sulphide.  The  glass,  reduced  to  powder,  is  boiled  with  bitar- 
trate  of  potash  as  a  source  of  oxide  of  antimony,  in  the 
pharmaceutical  preparation  of  tartar- emetic.  The  oxide  of 
antimony  is  dissolved  out  from  the  glass  by  acids,  and  a  sub- 
stance is  left  which  is  called  saffron  of  antimony.  This  last 
is  a  definite  compound  of  oxide  and  sulphide  of  antimony, 
Sb03  .  SSbSg,  which  also  occurs  as  a  mineral — namely,  red 
antimony  ore. 

Terchloride  of  antimony,  SbClg,  is  obtained  by  distilling 
either  metallic  antimony  or  the  tersulphide  of  antimony  with 
corrosive  sublimate.  When  heated  it  flows  like  an  oil,  and 
becomes  a  crystalline  mass  on  cooling.  It  is  a  powerful 
cautery.  This  salt  deliquesces  in  air,  and  becomes  turbid, 
owing  to  the  deposition  of  a  subsalt.  A  concentrated  solution 
of  chloride  of  antimony  is  also  obtained  by  dissolving  the 
sulphide  of  antimony  in  hydrochloric  acid.  When  this  solution 
is  thrown  into  water,  it  gives  a  white  bulky  precipitate,  which 
after  a  time  resolves  itself  into  groups  of  small  crystals,  having 
usually  a  fawn  colour ;  it  was  formerly  called  the  powder  of 
Algaroth.  These  small  crystals  are  an  oxychloride  of  anti- 
mony, which,  according  to  the  analyses  of  Johnston  and 
Malaguti,  contains  SSbClg  .  9Sb03. 

A  solution  of  terchloride  of  antimony,  to  which  water  is 
added,  and  then  a  sufficient  quantity  of  hydrochloric  acid  to 
redissolve  the  precipitate  thereby  produced,  gives  with  potash 
a  white  precipitate  of  the  hydrated  teroxide,  soluble  in  a  very 
large  excess  of  the  alkali.  Ammonia  forms  the  same  preci- 
pitate insoluble  in  excess.  Carbonate  of  potash,  or  soda,  pro- 
duces also  a  white  precipitate  of  the  hydrated  teroxide,  which 

B  4 


226  ANTIMONY. 

is  soluble  in  excess,  especially  of  the  potash-salt,  but  re- 
appears after  a  while.  These  reactions  are  greatly  modified 
by  the  presence  of  fixed  organic  acids,  especially  of  tartaric 
acid.  In  such  a  case,  water  forms  no  precipitate,  ammonia 
but  a  slight  one  and  after  some  time  only,  and  the  precipi- 
tate formed  by  potash  dissolves  easily  in  excess  of  the  alkali. 
(See  Tartar-emetic.) 

Terfluoride  of  antimony y  SbFg,  is  obtained,  by  treating  the 
teroxide  with  strong  hydrofluoric  acid,  in  colourless  crystals 
which  dissolve  in  water  without  decomposition.  It  unites 
with  fluoride  of  potassium,  forming  the  compound  3KF  .  SbFa 
and  similarly  with  fluoride  of  sodium  and  fluoride  of  ammo- 
nium. 

Sulphate  of  antimony,  SbOg  .  SSOg,  is  obtained,  by  boiling 
metallic  antimony  with  concentrated  sulphuric  acid,  as  a 
white  saline  mass,  which  is  decomposed  by  water. 

Oxalate  of  jmtash  and  antimony ^  KO  .  C2O3  4-  SbOg  .  3C2O3. 

—  This  is  a  double  crystallisable  salt  of  antimony,  which, 
like  the  tartrate  of  potash  and  antimony,  may  be  dissolved 
in  water  without  decomposition.  It  is  prepared  by  satur- 
ating binoxalate  of  potash  with  oxide  of  antimony.  It  is 
soluble  at  48°  in  ten  times  its  weight  of  Avater  (Lassaigne). 
According  to  Bussy,  when  binoxalate  of  potash  is  digested 
upon  oxide  of  antimony  in  excess,  two  salts  are  formed,  one 
in  oblique  prisms,  and  another  less  soluble,  in  intricate  small 
crystals ;  but  neither  is  very  stable.  The  former  is  decom- 
posed by  a  large  quantity  of  water :  its  analysis  gave 
3(KO  .  C2O,)  +  SbOg  .  3C2O3  +  GHO.* 

Tartrate  of  potash  and  antimony,  KO .  Sb  O3  +  C8H4O1Q.2HO. 

—  This  salt,  the  tartar-emetic  or  potash  tartrate  of  anti- 
mony of  pharmacy,  is  prepared  by  neutralising  bitartrate 
of  potash  with  oxide  of  antimony ;  the  oxide  obtained  by  de- 
composing the  chloride  or  sulphate  of  antimony  with  water 
answers  best  for  the  purpose.     A  quantity  of  oxide  of  anti- 

•  J.  Pharm.  1838,  p.  509. 


f  TARTAR-EMETIC.  227 

mony  may  be  boiled  with  three  or  four  times  its  weight  of 
water,  and  bitartrate  of  potash  added  in  small  quantities  till 
the  oxide  is  entirely  dissolved.  The  filtered  solution  yields 
the  salt,  on  cooling,  in  large  transparent  crystals,  the  form  of 
which  is  an  octohedron  with  a  rhombic  base ;  they  become 
white  in  the  air,  and  lose  their  water  of  crystallisation.  They 
are  soluble  in  14  times  their  weight  of  cold  water,  and  in  1'88 
parts  of  boiling  water,  but  not  in  alcohol.  The  mother-liquor 
of  these  crystals  becomes  a  syrupy  liquid,  and  dries  up  into 
a  gummy  mass  without  crystallising,  when  oxide  of  antimony 
has  been  dissolved  in  excess  by  the  acid  tartrate  in  prepar- 
ing the  salt.  Potash  added  to  a  solution  of  the  salt  throws 
down  the  teroxide  of  antimony,  but  the  precipitate  is  easily 
soluble  in  excess  of  potash.  Ammonia  forms  no  precipitate 
at  first,  and  but  a  slight  one  after  standing.  Alkaline  car^ 
bonates  form  a  precipitate  of  the  teroxide  insoluble  in  excess 
of  the  reagent.  With  hydrosulphuric  acid,  the  reaction  is 
the  same  as  with  other  salts  of  antimony.  (See  p.  224.)  Salts 
of  the  earths  and  basic  metallic  oxides,  such  as  baryta  and 
oxide  of  silver  J  throw  down  from  its  solution  a  compound  of 
the  tartrate  of  antimony  with  tartrate  of  baryta,  tartrate  of 
silver,  &c.  (Wallquist.)  Strong  acids  decompose  the  salt, 
and  produce  a  precipitate  which  is  a  mixture  of  bitartrate  of 
potash  with  oxide  of  antimony,  or  with  a  subsalt  of  that 
oxide. 

This  salt  was  formerly  described  as  a  double  tartrate  of 
potash  and  antimony,  or,  abstracting  its  water  of  crystallisa- 
tion, which  is  differently  stated  at  2  and  3  equivalents,  as 
KO .  (C4H2O5)  +  SbOa .  (C4H2O5) .  When  the  atomic  weight 
of  tartaric  acid  is  doubled,  and  it  is  represented  as  a  bibasic 
acid,  the  formula  for  dry  tartar-emetic  becomes  KO .  SbOg. 
(CgH^Ojo).  In  comparing  the  last  formula  with  that  of  bi- 
tartrate of  potash,  represented  also  as  a  bibasic  salt,  KO . 
HO .  (CgH^Oio),  it  is  observed  that  1  eq.  of  oxide  of  anti- 
mony takes  the  place  of  I  eq.  of  water  as  base,  although  the 


228  ANTIMONY. 

former  contains  3  eq.  of  oxygen,  and  the  latter  only  one.  Tar- 
trate of  potash  and  antimony  is,  in  this  respect,  an  anomalous 
salt.  Another  equally  remarkable  fact  respecting  this  salt 
has  been  observed  by  M.  Dumas,  namely,  that  2  eq.  of  water 
are  separated  from  the  anhydrous  salt  at  428°,  leaving  a 
substance  of  which  the  elements  are  CgH20j2  SbK.  The 
first  part  of  this  formula  C8H2O12,  M.  Dumas  looks  upon  as 
a  quadribasic  salt-radical,  existing  in  the  tartrates,  which  in 
hydrated  tartaric  acid  is  united  with  4H,  in  bitartrate  of 
potash  with  311  +  K,  and  in  tartrate  of  antimony  and  potash 
with  Sb  +  K.  Here  Sb  is  found  equivalent  to  and  capable 
of  replacing  3H.  Tartrate  of  antimony  and  potash  might, 
therefore,  be  represented  by  KSb(C8H20i2)  +  2H0  +  water 
of  crystallisation.  If  Sb02  be  regarded  as  a  radical  capable 
of  replacing  1  eq.  of  hydrogen  (similar  to  uranyl,  U2O2, 
the  hypothetical  radical  of  the  uranic  salts),  the  formula 
of  tartar-emetic  dried  at  212°  may  be  written  as  CgH^K 
(Sb02)Oi2,  and  that  of  the  salt  dried  between  392°  and 
428°,  as  C8H2K(Sb02)Oio. 

Antimonic  acid,  SbO^,!  60*24  or  2003. — This  compound  is 
obtained  in  the  hydrated  state :  1 .  By  treating  antimony 
with  nitric  acid,  or  with  aqua-regia  containing  excess  of 
nitric  acid.  2.  By  decomposing  pentachloride  of  antimony 
with  water.  3.  By  precipitating  a  solution  of  antimoniate  of 
potash  with  an  acid. 

The  hydrated  acid  obtained  by  either  of  these  methods 
gives  off  its  water  at  a  moderate  heat,  and  yields  anhydrous 
antimonic  acid  in  the  form  of  a  yellowish  powder,  which  is 
tasteless,  insoluble  in  water,  decomposes  alkaline  carbonates, 
and,  when  heated  to  redness,  gives  off  oxygen,  and  is  con- 
verted into  antimoniate  of  antimonic  oxide,  SbOg  .  SbOg. 

The  hydrates  obtained  by  the  three  methods  above  de- 
scribed are  by  no  means  identical.  The  acid  in  the  first  is 
monobasic,  whereas  in  the  other  two  it  is  bibasic.  The  bi- 
basic  acid  is  distinguished  by  the  name  of  met  antimonic  acid. 


ANTIMONIATES.  229 

while  the  monobasic  acid  is  called  simply  antimonic  acid 
(Fremy) . 

Antimonic  acid  forms  neutral  or  normal  salts,  containing 
MO .  SbOg,  and  acid  salts  whose  formula  is  MO .  (Sb05)2.  Met- 
antimonic  acid  forms  neutral  salts  containing  (MO)  2 .  SbOg, 
and  acid  salts  containing  (MO)2.(Sb05)2,  or  MO.SbOg, 
so  that  the  acid  metantimoniates  are  isomeric  or  polymeric 
with  the  neutral  antimoniates.  An  acid  metantimoniate 
easily  changes  into  a  neutral  antimoniate.  The  metanti- 
moniates of  potash,  soda,  and  ammonia  are  crystalline ;  the 
antimoniates  of  the  same  bases  are  gelatinous  and  uncrystal- 
lisable.  The  soluble  acid  metantimoniates  form  a  crystalline 
precipitate  with  salts  of  soda;  the  soluble  antimoniates  do 
not  form  any  such  precipitate  (Fremy). 

Antimoniates  of  potash. — The  neutral  salt,  KO.SbO5.5HO, 
is  obtained  by  fusing  1  part  of  antimony  with  4  parts  of  nitre, 
digesting  the  fused  mass  in  tepid  water  to  remove  nitrate  and 
nitrite  of  potash,  and  boiling  the  residue  for  an  hour  or  two 
with  water.  The  white  insoluble  mass  of  anhydrous  anti- 
moniate is  thereby  transformed  into  a  hydrate  containing 
5  eq.  water,  which  is  soluble.  The  solution  when  evaporated 
leaves  this  hydrate  in  the  form  of  a  gummy  uncrystallisable 
mass,  which  gives  off  2  eq.  of  water  at  320°,  and  the  whole  at 
a  higher  temperature. 

Acid  antimoniate  of  potash,  KO .  (Sb05)2  is  obtained  by 
passing  carbonic  acid  gas  through  a  solution  of  the  neutral 
antimoniate.  It  is  white,  crystalline,  perfectly  insoluble  in 
water,  and  is  converted  into  the  neutral  salt  when  heated 
with  excess  of  potash.  This  salt  is  the  antimonium  diapho- 
reticum  lavatum  of  the  pharmacopoeias  (Fremy) . 

Neutral  metantimoniate  of  potash,  21L0.^h0^y  is  prepared 
by  fusing  antimonic  acid  or  neutral  antimoniate  of  potash 
with  a  large  excess  of  potash.  The  fused  mass  dissolves  in  a 
small  quantity  of  water,  and  the  solution  evaporated  in  vacuo 
yields   crystals   of  the   neutral  metantimoniate.     This    salt 


230  ANTIMONY. 

dissolves  freely  and  without  decomposition  in  warm  water 
containing  excess  of  potash;  but  cold  water  or  alcohol  de- 
composes it  into  potash  and  the  acid  metantimoniatc.  Hence 
the  aqueous  solution  of  this  salt  gives  a  precipitate,  after  a 
while,  with  salts  of  soda  (Fremy) . 

Acid  metantimoniate  of  potash,  KO  .  SbOg  +  THO,  some- 
times called  granular  antimoniate  of  potash.  —  This  salt  is 
used  as  a  test  for  soda.  To  obtain  it,  the  neutral  antimoniate 
is  first  prepared  and  dissolved  in  the  manner  above  described  ; 
the  solution  filtered  to  separate  any  acid  antimoniate  that 
may  remain  undissolved;  then  evaporated  to  a  syrup  in  a 
silver  vessel ;  and  hydrate  of  potash  added  in  lumps  to  convert 
the  antimoniate  into  metantimoniate.  The  evaporation  is 
continued  till  the  liquid  begins  to  crystallise,  which  is  ascer- 
tained by  taking  out  a  drop  now  and  then  upon  a  glass  rod, 
and  the  liquid  is  left  to  cool.  A  crystalline  mass  is  thus 
obtained,  consisting  of  neutral  and  acid  metantimoniate  of 
potash ;  the  alkaline  liquor  is  then  decanted,  and  the  salt  di'ied 
upon  filtering  paper  or  unglazed  porcelain  (Fremy).  This 
salt  may  also  be  prepared  by  treating  terchloridc  of  antimony 
with  an  excess  of  potash  sufficient  to  redissolve  the  precipitate 
first  formed,  and  adding  permanganate  of  potash  till  the 
solution  acquires  a  faint  rose  colour.  The  liquid,  filtered 
and  evaporated,  yields  crystals  of  the  granular  metantimoniate 
(Reynoso).  This  salt  is  sparingly  soluble  in  cold  water,  but 
dissolves  readily  in  water  between  113°  and  122°.  When 
boiled  with  water  for  a  few  minutes,  or  kept  in  contact  with 
water  for  some  time,  it  is  converted  into  the  neutral  anti- 
moniate. It  must  therefore  be  preserved  in  the  solid  state, 
and  dissolved  just  before  it  is  required  for  use.  A  small 
quantity  of  it  is  then  treated  with  about  twice  its  weight  of 
cold  water  to  remove  excess  of  potash,  and  convert  any 
neutral  metantimoniate  into  the  acid  salt;  the  liquid  de- 
canted; the  remaining  salt  rapidly  washed  three  or  four 
times  with  cold  water ;  then  left  in  contact  with  water  for  a 


ANTIMONIATES.  231 

few  minutes,  and  the  liquid  filtered.  On  adding  to  the  solu- 
tion thus  obtained,  a  small  quantity  of  any  soda-salt,  a  crys- 
talline precipitate  is  formed,  consisting  of  acid  metantimo- 
niate  of  soda,  NaO  .  SbOg  +  7H0.  This  reaction  is  apparent 
in  a  solution  containing  only  1  part  of  soda  in  300.  In  strong 
solutions  of  soda,  the  precipitate  appears  immediately,  but  in 
dilute  solutions  only  after  a  while,  the  crystals  being  depo- 
sited on  the  sides  of  the  vessel.  An  excess  of  potash  in  the 
reagent  also  retards  the  precipitation  (Fremy*) . 

Antimoniates  of  ammonia. — ^When  the  metantimonic  acid, 
obtained  by  decomposing  pentachloride  of  antimony  with 
water,  is  treated  with  ammonia,  part  of  it  dissolves,  and  a 
solution  is  formed  containing  neutral  metantimoniate  of  am- 
monia.  A  few  drops  of  alcohol  added  to  the  solution,  throw 
down  a  precipitate  consisting  of  acid  metantimoniate  of  am- 
monia, NH^O  .  SbOg  +  6H0.  This  salt  is  slightly  soluble,  and 
its  solution  precipitates  soda-salts.  It  changes  spontaneously 
in  a  few  days,  even  when  kept  in  a  close  vessel,  into  neutral  an- 
timoniate  of  ammonia,  which  is  completely  insoluble  in  water. 
The  same  change  is  instantly  produced  in  it  by  heat  (Fremy) . 

Antimoniate  of  lead,  PbO .  SbOg,  may  be  obtained  as  a 
yellow  powder  by  fusing  antimonic  acid  with  oxide  of  lead,  or 
as  a  white  hydrate  by  precipitation  :  the  hydrate  gives  off  its 
water  when  heated,  and  turns  yellow.  This  salt  is  used  as  a 
pigment  under  the  denomination  of  Naples  yellow. 

Antimoniate  of  antimoni/,  SbOg.SbOg.  or  Sb04,  is  obtained 
by  the  action  of  heat  upon  antimonic  acid,  by  roasting  the 

*  Traite  de  Cliimie  Generale,  par  Pelouze  et  Fremy,  2me.  ed.  t.  3.  pp.  151. 
157.  According  to  Heflfter  (Pogg.  Ann.  Ixxxvi.  418.),  the  granular  antimoniate 
of  potash  is  KO  .HO  +  12(KO.Sb05  +  7HO)  ;  the  precipitated  soda-salt  is 
similarly  constituted ;  and  by  treating  the  solution  of  this  salt  in  boiling 
water  with  salts  of  the  earths  and  metallic  oxide?,  precipitates  are  obtained, 
also  of  similar  composition,  or  differing  only  in  the  water  which  they 
contain.  Heffter's  formulae  were  calculated  according  to  the  old  equivalent  of 
antimony,  129  ;  but  Schneider  has  shown  that,  on  re-calculating  the  analyses 
with  the  lower  equivalent  120'24,  the  numbers  of  the  equivalents  of  base  and 
acid  come  out  equal. 


233  ANTIMONY. 

teroxide  or  tersulphide,  or  by  treating  powdered  antimony  with 
excess  of  nitric  acid.  It  is  white,  infusible,  and  unalterable 
by  heat ;  slightly  soluble  in  water.  It  was  formerly  regarded 
as  a  distinct  acid,  Sb04,  ^'^^  called  antimonious  acid ;  but  it 
does  not  form  salts;  and,  when  boiled  with  bitartrate  of 
potash,  it  is  resolved  into  cream  of  tartar,  which  dissolves, 
and  a  residue  of  antimonic  acid. 

Pentasulphide  of  antimony,  Sulphantimonic  acid,  SbOg,  is 
obtained  by  passing  hydrosulphuric  acid  gas  into  an  acid 
solution  of  pentachloride  of  antimony,  or  into  the  solution 
of  an  alkaline  antimoniate.  It  has  an  orange-colour  much 
less  red  than  the  tersulphide;  it  is  the  golden  sulphuret  of 
antimony  of  several  pharmacopoeias.  It  combines  with  basic 
metallic  sulphides,  forming  the  sulphantimoniates.  The  sodium- 
salt,  3NaS .  SbSg,  which  is  sometimes  used  in  medicine,  is 
obtained  by  mixing  18  parts  of  finely  pounded  tersulphide  of 
antimony,  12  parts  of  dry  carbonate  of  soda,  13  parts  of  lime, 
and  3  J  parts  of  sulphur ;  triturating  the  mixture  for  about  half 
an  hour ;  leaving  it  for  two  or  three  days  in  a  flask  filled  with 
water,  and  shaking  it  from  time  to  time ;  then  filtering  and 
evaporating,  first  over  tlie  open  fire,  afterwards  in  vacuo.  The 
salt  is  thus  obtained  in  large  regular  tetrahedrons  of  a  pale  yel- 
low colour.  It  is  very  soluble  in  water,  and  is  decomposed  by 
acids,  which  throw  down  hydrated  pentasulphide  of  antimony. 

Pentachloride  of  antimony,  SbClg,  is  obtained  by  heating 
metalUc  antimony  in  a  current  of  dry  chlorine,  and  distilhng 
the  product  in  a  dry  retort,  rejecting  the  first  portions  of  the 
distillate,  which  contain  excess  of  chlorine.  It  is  a  yellowish, 
very  volatile  liquid,  which  emits  suffocating  vapours.  Water 
first  converts  it  into  a  crystalline  hydrate,  and  then  decomposes 
it,  forming  antimonic  acid  :  SbCl5  4-5HO  =  Sb05  +  5HCl. 
It  absorbs  ammonia  and  phosphurctted  hydrogen,  forming 
red-brown  solid  compounds.  It  absorbs  olefiant  gas  as  readily 
as  chlorine,  and  forms  Dutch  liquid.  It  likewise  absorbs 
hydrosulphuric  acid  gas  at  ordinary  temperatures,  forming  a 


ANTIMONIURETTED    HYDROGEN.  233 

white  crystalline  mass,  consisting  oi  chlorosulphide  of  antimony j 
SbClgSg,  exactly  analogous  to  chlorosulphide  of  phosphorus 
PCI3S2.  Pentasulphide  of  antimony,  treated  with  dry  chlorine 
aided  by  heat,  forms  a  white  pulverulent  compound,  containing 
SbClgSg,  or  SbClg.SSClj  this  compound  is  decomposed  at 
572°  (300°  C.)  into  chlorine,  chloride  of  sulphur,  and  ter- 
chloride  of  antimony.  Pentachloride  of  antimony  combines 
with  hydrocyanic  acid,  forming  a  white,  crystalline,  volatile 
compound,  composed  of  SbClg.SHCy.  It  also  combines  with 
chloride  of  cyanogen. 

Antimoniuretted  hydrogen.  — This  compound  is  obtained  by 
dissolving  an  alloy  of  zinc  and  antimony  in  hydrochloric  or 
dilute  sulphuric  acid,  or  by  dissolving  zinc  in  either  of  these 
dilute  acids  containing  oxide  or  chloride  of  antimony,  tartar- 
emetic,  &c.  The  gas,  however,  always  contains  more  or  less 
free  hydrogen.  Its  comparative  purity  may  be  tested  by 
means  of  a  solution  of  nitrate  of  silver,  which  absorbs  the 
antimoniuretted  hydrogen,  and  leaves  the  free  hydrogen.  An 
alloy  of  2  parts  zinc  and  1  part  antimony  yields  the  purest 
gas;  an  alloy  containing  a  larger  proportion  of  antimony 
gives  more  free  hydrogen ;  and  an  alloy  of  equal  parts  of  the 
two  metals  yields  scarcely  anything  but  free  hydrogen.  As 
the  compound  has  never  been  obtained  in  a  state  of  purity, 
its  composition  has  not  been  correctly  ascertained,  but  it  is 
probably  SbH3. 

Antimoniuretted  hydrogen  is  a  colourless  gas,  and  when 
free  from  arsenic,  quite  inodorous.  It  is  insoluble  in  water, 
and  in  alkaline  liquids ;  with  solutions  of  silver  or  mercury 
it  forms  precipitates  containing  silver  or  mercury,  together 
with  antimony.  When  burned  from  a  jet,  it  deposits,  on  a 
plate  of  porcelain,  metallic  spots,  greatly  resembling  those  of 
arsenic,  but  differing  from  the  latter  in  possessing  less  lustre 
and  in  not  being  soluble  in  hypochlorite  of  soda.  They  may 
also  be  dissolved  in  aqua-regia  or  in  permanganate  of  potash 
(p.  224),  and  the  solution  wiU  give  the  characteristic  orange 


231  ANTIMONY. 

precipitate  with  hydrosulphuric  acid.  A  metallic  deposit  may 
also  be  obtained  by  heating  a  glass  tube  through  which  the 
gas  is  passed ;  and  this  deposit,  when  sublimed,  will  not  exhibit 
the  characters  of  arsenic  (p.  216). 

Alloys  of  antimony  with  potassium  or  sodium  may  be  ob- 
tained by  igniting  metallic  antimony,  or  its  oxide  or  sulphide, 
with  an  organic  salt  of  potasli  or  soda.  Thus,  when  5  parts 
of  crude  tartar  and  4  parts  of  antimony  are  slowly  heated 
in  a  covered  crucible  till  the  mixture  becomes  charred,  then 
heated  to  whiteness  for  an  hour,  and  left  to  cool,  a  crystalline 
regulus  is  obtained  containing  12  per  cent,  of  potassium.  This 
alloy  decomposes  water  rapidly,  and  oxidises  slowly  in  the  air 
when  in  the  compact  state,  but  becomes  heated  and  takes  fire 
when  rubbed  to  powder. 

A  mixture  of  7  parts  of  antimony  and  3  parts  of  iron,  heated 
to  whiteness  in  a  crucible  lined  with  charcoal,  forms  a  white, 
very  hard,  slightly  magnetic  alloy,  which  gives  sparks  when 
filed.  It  is  always  formed  when  sulphide  of  antimony  is 
reduced  by  iron  in  excess. 

With  zinc,  antimony  forms  alloys  of  definite  crystalline 
character.  A  fused  mixture  of  the  two  metals,  containing 
from  43  to  70  per  cent,  of  zinc,  deposits  by  partial  cooling, 
silver-white  rhombic  prisms,  containing  from  43  to  64  per 
cent,  of  zinc.  The  alloy  containing  exactly  43  per  cent,  of 
zinc,  appears  to  be  a  definite  compound,  stibiotinzincyl,  SbZug. 
Mixtures  containing  from  33  to  20  per  cent,  of  zinc  deposit 
rhombic  crystals  containing  from  35  to  21  per  cent,  of  zinc. 
The  alloy  containing  exactly  33  per  cent,  is  stibiobizincyl, 
SbZn2.  These  alloys,  especially  SbZn3,  decompose  water  with 
evolution  of  hydrogen  at  the  boiling  heat,  and  very  rapidly 
under  the  influence  of  acids  (J.  P.  Cooke  *). 

Type-metal,  is  an  alloy  of  antimony  and  lead,  usually  con- 
taining 76  per  cent,  of  lead,  which  corresponds  nearly  with 
the  formula  V\^h. 

*  Sm.  Aui.  J.  [2.]  xviii.  229;  xx.  222. 


ESTIMATION    OF    ANTIMONY.  235 


ESTIMATION     OF     ANTIMONY,     AND     METHODS     OP     SEPARATING 
IT    FROM    THE    PRECEDING    METALS. 

Antimony  cannot  be  estimated  in  the  form  of  antimonious 
or  antimonic  acid,  because  we  can  never  be  sure  of  the  purity 
of  those  bodies.  The  best  mode  of  proceeding  is  to  precipi- 
tate it  by  hydrosulphuric  acid,  collect  the  sulphide  of  anti- 
mony on  a  weighed  filter,  and,  after  ascertaining  the  total 
quantity  of  the  precipitate,  estimate  the  proportion  of  sulphur 
in  it  in  the  manner  already  described  with  reference  to  sul- 
phide of  arsenic  (p.  219).  Or  the  sulphide  of  antimony  may 
be  decomposed  by  heating  it  in  a  current  of  hydrogen  gas, 
whereupon  hydrosulphuric  acid  and  sulphur-vapour  escape, 
and  metallic  antimony  remains  behind.  For  this  purpose,  a 
weighed  portion  of  the  sulphide  is  placed  in  a  small  porcelain 
crucible  ha^dng  a  hole  in  its  cover,  through  which  a  tube 
passes  to  convey  the  hydrogen.  The  temperature  is  gradually 
raised,  and  the  process  continued  till  the  weight  of  the  cru- 
cible no  longer  varies.  The  reduction  may  also  be  performed 
in  a  bulb-tube. 

When  antimonious  and  antimonic  acids  occur  together  in 
solution,  the  total  quantity  of  antimony  may  be  ascertained 
by  treating  one  portion  of  the  liquid  in  the  manner  just 
described,  and  the  quantity  existing  as  antimonious  acid  may 
be  determined  in  another  portion  by  means  of  terchloride  of 
gold,  2  eq.  of  precipitated  gold  corresponding  to  3  eq.  of  anti- 
monious acid : 

2AUCI3  -I-  6H0  +  3Sb03  =  2Au  +  6HC1  +  3Sb05. 

The  separation  of  antimony  from  the  alkalies  and  earths j 
and  from  those  metals  which  are  not  precipitated  from  their 
acid  solutions  by  hydrosulphuric  acid,  is  effected  by  means  of 
that  reagent. 

To  separate  antimony  from  cadmium^  copper ,  and  leadj  the 

VOL.  II.  s 


236  ANTIMONY. 

solution,  after  being  neutralised  with  ammonia,  is  mixed  with 
sulphide  of  ammonium  containing  excess  of  sulphur.  The 
sulphide  of  antimony  then  dissolves,  the  other  sulphides 
remaining  undissolved ;  and  on  mixing  the  filtrate  with  acetic 
acid  (hydrochloric  acid  might  redissolve  a  portion  of  the  pre- 
cipitate, especially  as  the  liquid  becomes  heated),  the  sulphide 
of  antimony  is  reprecipitated,  and  may  be  treated  as  above. 

When  antimony  is  combined  with  any  of  the  preceding 
metals  in  the  form  of  an  alloy,  it  may  be  separated  by 
treating  the  alloy  with  nitric  acid,  whereby  the  other  metals 
are  dissolved,  and  the  antimony  converted  into  insoluble 
antimonic  acid.  This  method  is,  however,  not  rigidly  exact; 
for  the  nitric  acid  dissolves  a  small  portion  of  the  antimony. 

Separation  of  antimony  from  arsenic  and  tin. — The  separa- 
tion of  these  metals  is  attended  with  considerable  difficulty. 
The  best  mode  of  effecting  it  is  to  convert  them  into  arsen- 
iate,  stannate,  and  antimoniatc  of  soda,  and  treat  the  mixture 
with  dilute  alcohol,  which  dissolves  the  arseniate  and  stannate 
of  soda,  and  leaves  the  antimoniate  undissolved. 

If  the  three  metals  exist  together  in  solution,  they  must  be 
precipitated  as  sulphides  by  hydrosulphuric  acid,  and  the 
precipitate  treated  by  one  of  the  following  methods  :  — 

(1.)  The  precipitated  sulphides  are  fused  in  a  silver  cru- 
cible with  a  mixture  of  hydrate  of  soda  and  nitre  :  or,  better, 
they  are  oxidised  by  heating  them  with  strong  nitric  acid ; 
the  solution,  together  Avith  the  insoluble  stannic  and  anti- 
monic acids,  mixed  with  excess  of  caustic  soda,  and  evapo- 
rated to  a  small  bulk ;  then  transferred  to  a  silver  crucible, 
evaporated  to  dryness,  and  kept  for  some  time  in  a  state  of 
red  hot  fusion.  The  fused  mass,  consisting  of  arseniate, 
stannate,  and  antimoniate  of  soda,  is  disintegrated  by  diges- 
tion in  warm  water;  the  contents  of  the  crucible  trans- 
feiTcd  to  a  beaker-glass;  and  the  crucible  well  rinsed  out 
with  a  measured  quantity  of  water.  The  greater  part  of  the 
arseniate  and  stannate  of  soda  then  dissolves,  while  the  anti- 


SEPARATION    OF   ANTIMONY    FROM    TIN    AND    ARSENIC.       237 

moniate  remains  undissolved.  But  to  effect  complete  separa- 
tion, a  quantity  of  alcohol  of  sp.  gr.  0'833  is  added,  equal 
in  bulk  to  one-third  of  the  water  used;  the  mixture  left 
to  stand  for  24  hours  and  frequently  stirred ;  and  the  anti- 
moniate  of  soda,  which  has  then  completely  settled  down, 
is  collected  on  a  filter  and  washed,  first,  with  a  mixture  of 
1  volume  of  the  same  alcohol  to  3  vols,  of  water,  then  with 
1  vol.  alcohol  to  2  vols,  water ;  next,  with  a  mixture  of  equal 
measures  of  water  and  alcohol;  and,  lastly,  with  3  vols, 
alcohol  to  1  vol.  water  (H.  Eose).* 

(2.)  The  precipitated  sulphides  of  the  three  metals  are 
dissolved  in  a  mixture  of  sulphide  of  sodium  and  caustic  soda, 
and  the  liquid  mixed  with  a  solution  of  hypochlorite  of  soda. 
The  sulphides  are  thereby  oxidised  and  converted  into  arsenic, 
stannic,  and  antimonic  acids,  which  combine  with  the  soda, 
and  may  be  separated  by  treatment  with  dilute  alcohol,  and 
washing,  as  in  Rosens  process.  This  method  is  due  to  Dr. 
Williamson;  it  is  easier  of  execution  than  the  former,  as 
the  fused  mixture  of  the  soda-salts  is  very  hard,  and  difficult 
to  disintegrate  by  water. 

The  antimoniate  of  soda,  separated  by  either  of  these  pro- 
cesses, is  digested  in  a  mixture  of  hydrochloric  and  tartaric 
acids,  which  dissolves  it  completely ;  the  antimony  then  pre- 
cipitated by  hydrosulphuric  acid ;  and  its  quantity  estimated 
in  the  manner  already  described  (p.  235). 

The  filtrate  containing  the  arseniate  and  stannate  of  soda 
is  supersaturated  with  hydrochloric  acid,  which  throws  down 
a  bulky  precipitate  of  arseniate  of  stannic  oxide ;  hydrosul- 
phuric acid  gas  passed  through  the  liquid  till  the  white  preci- 
pitate is  completely  converted  into  a  brown  mixture  of  the 
sulphides  of  tin  and  arsenic ;  the  whole  left  to  stand  till  the 
odour  of  hydrosulphuric  acid  is  no  longer  perceptible;  the 
precipitate  collected  on  a  weighed  filter;   and   the   filtrate 

*  Handb.  d.  anal.  Chem.  1851.  ii.  429. 
s  2 


238  ANTIMONY. 

heated  for  some  time  to  expel  the  greater  part  of  the  alcohol ; 
then  mixed  with  sulphurous  acid,  and  again  treated  with 
hydrosulphuric  acid,  whereby  a  small  quantity  of  sulphide  of 
-arsenic  is  generally  precipitated.  This  quantity  of  sulphide 
of  arsenic  being  quite  free  from  tin,  need  not  be  added  to  the 
mixed  sulphides  on  the  filter. 

These  mixed  sulphides  are  dried  at  212°,  their  total  weight 
determined,  and  a  known  quantity  heated  in  a  stream  of 
hydrosulphuric  acid  gas  in  the  manner  described  at  page  220. 
The  residual  sulphide  of  tin  is  then  converted  into  stannic 
oxide,  and  the  sublimed  sulphide  of  arsenic,  together  with 
the  small  quantity  separately  precipitated,  is  converted  into 
arsenic  acid  by  treatment  with  hydrochloric  acid  and  chlorate 
of  potash,  and  the  arsenic  precipitated  as  ammonio-magnesian 
arseniate  (H.  Rose). 

If  the  three  metals  are  in  the  state  of  solid  oxides,  the 
mixture  may  be  dissolved  in  hydrochloric  acid,  with  addition 
of  tartaric  acid,  and  the  metals  precipitated  as  sulphides  as 
before.  If  the  metals  are  mixed  in  the  form  of  an  alloy,  they 
may  be  dissolved  in  aqua-regia,  tlie  solution  mixed  with  tar- 
taric acid,  then  diluted,  and  precipitated  in  the  same  manner. 

The  method  just  described  may,  of  course,  be  applied  to 
the  separation  of  antimony  from  tin  or  from  arsenic  alone. 
In  these  cases,  however,  simpler  methods  may  often  be  ad- 
vantageously adopted. 

Separation  of  antimony  from  tin — When  these  two  metals 
exist  together  in  solution,  and  the  sum  of  their  weights  is 
known,  the  separation  may  be  effected,  and  the  weights  of 
the  two  determined,  by  immersing  in  the  solution  a  piece  of 
pure  tin,  which  precipitates  the  antimony  in  the  form  of  a 
l^lack  powder.  To  render  the  precipitation  complete,  a  gentle 
heat  must  be  applied,  and  the  solution  must  contain  excess  of 
acid.  The  antimony  is  collected  on  a  weighed  filter,  dried  at 
a  gentle  heat,  and  weighed.  If  the  sum  of  the  weights  is  not 
previously  known,  the  metals  must  be  precipitated  together 


SEPARATION    OF   ANTIMONY  TROM    ARSENIC.  239 

by  zinc  from  a  known  quantity  of  the  solution,  and  the  anti- 
mony precipitated  by  tin  from  another  portion.  When  the 
two  metals  exist  together  in  an  alloy,  a  portion  of  the  alloy 
must  be  weighed,  then  dissolved  in  aqua-regia,  and  the  solu- 
tion mixed  with  tartaric  acid,  diluted  with  water,  and  treated 
as  above. 

Another  method  of  separation  is  to  precipitate  the  two 
metals  with  zinc,  and  treat  the  precipitate  with  strong  hydro- 
chloric acid  without  previously  decanting  the  solution  of 
chloride  of  zinc.  The  tin  then  dissolves,  while  the  antimony 
remains  undissolved,  the  presence  of  the  chloride  of  zinc 
diminishing  its  tendency  to  dissolve  in  the  acid.  The  tin 
may  afterwards  be  precipitated  by  hydrosulphuric  acid,  and 
the  sulphide  converted  into  stannic  oxide,  by  treating  it  with 
strong  nitric  acid  (Levol).* 

Separation  of  antimony  from  arsenic. — When  these  two 
metals  are  associated  in  the  metallic  state,  they  may  be  com- 
pletely separated  by  heating  the  alloy  in  a  stream  of  carbonic 
acid,  the  arsenic  then  volatilising,  and  the  antimony  remain- 
ing. Antimony  is,  however,  the  only  metal  from  which  ar- 
senic can  be  completely  separated  in  this  manner ;  hence,  if 
the  alloy  contains  any  other  metal,  some  of  the  arsenic  will 
be  retained,  and  the  method  is  no  longer  applicable. 

When  this  is  the  case,  the  alloy  may  be  dissolved  in  aqua 
regia,  or  in  hydrochloric  acid  to  which  chlorate  of  potash  is 
gradually  added ;  the  solution  diluted  with  water  after  addi- 
tion of  tartaric  acid ;  then  mixed  with  a  considerable  quantity 
of  chloride  of  ammonium  and  excess  of  ammonia;  and  the 
arsenic  precipitated  as  ammonio-magnesian  arseniate  by  addi- 
tion of  sulphate  of  magnesia.  The  antimony  may  then  be 
precipitated  from  the  filtrate  by  hydrosulphuric  acid. 

*  Ann.  Ch.  Phys.  [3.]  xiii.  125. 


S  3 


240 


BISMUTH. 


SECTION    III. 


BISMUTH. 


Eq.  213,  or  26625;  Bi. 

Bismuth  is  generally  found  in  the  metallic  state,  disseminated 
in  quartz-rock ;  but  occurs  also  as  an  oxide,  carbonate,  and 
sulphide,  either  alone  or  associated  with  other  metals ;  also  in 
combination  with  tellurium.  Native  bismuth  is,  however,  the 
only  mineral  which  occui*s  in  sufficient  abundance  for  the 
economical  extraction  of  the  metal.  The  process  of  extraction 
as  performed  in  Saxony,  whence  all  the  bismuth  of  commerce 
is  obtained,  is  veiy  simple,  the  mineral  being  merely  heated  in 
close  vessels,  so  as  to  melt  the  bismuth,  and  thereby  separate  it 
from  the  gangue  or  accompanying  rock.  The  fusion  is  per- 
formed in  iron  tubes,  laid  in  an  inclined  position,  in  a  furnace. 
{Fig.  11.)     The  ore  is  introduced  at  the  upper  end,  d,  which 

is  then  plugged.  The 
other  end,  6,  is  closed 
with  an  iron  plate 
having  an  aperture, 
0,  through  which  the 
melted  metal  runs 
into  earthen  pots,  a, 
heated  by  a  few  coals 
placed  in  the  space, 
K,  below,  so  as  to 
keep  the  metal  in 
the  melted  state.  It  is  then  ladled  out  and  run  into  moulds. 
The  crude  metal  thus  obtained  is  afterwards  fused  with  1-lOth 
of  its  weight  of  nitre,  to  free  it  from  sulphur,  arsenic,  and 
certain  foreign  metals. 

Commercial  bismuth,  however,  is  still  somewhat  impure. 
To  free  it  completely  from  other  metals,  it  is  dissolved  in 


Fii?.  11. 


OXIDES    OF    BISMUTH.  241 

nitric  acid,  the  clear  liquid  decanted  and  mixed  with  water, 
which  throws  down  a  subnitrate  of  bismuth;  and  this  com- 
pound is  reduced  at  a  moderate  heat,  either  with  black  flux, 
or  in  a  crucible  lined  with  charcoal. 

Bismuth  crystallises  in  octohedrons  and  cubes.  It  may  be 
obtained  in  very  beautiful  crystals,  by  fusing  several  pounds 
of  the  ordinary  metal  in  a  crucible  or  iron  ladle,  adding 
nitre  from  time  to  time,  and  stirring,  till  a  portion  of  the 
fused  metal,  taken  out  and  exposed  to  the  air,  no  longer 
assumes  an  indigo  colour,  changing  to  violet  or  rose  and  dis- 
appearing on  cooling,  but  a  fine  green  or  golden  tint,  which  it 
retains  on  cooling ;  then  leaving  the  metal  to  cool  slowly,  on 
a  hot  sand-bath,  for  instance,  till  a  crust  forms  on  the  surface ; 
piercing  this  crust  with  a  hot  coal ;  and  pouring  out  the  por- 
tion which  still  remains  liquid.  On  subsequently  detaching 
the  crust,  the  inner  surface  of  the  metal  is  found  to  be  covered 
with  beautiful  fretted  cubes,  like  those  of  common  salt. 

Bismuth  is  moderately  hard,  slightly  sonorous,  and  brittle, 
but  may  be  somewhat  extended  by  careful  hammering.  Its 
colour  is  reddish  tin- white,  with  moderate  lustre.  The 
specific  gravity  of  pure  bismuth  is  96542  (Karsten),  9'799 
(Marchand  and  Scherer) ;  of  commercial  bismuth,  9' 822 
(Brisson),  9'833  (Herapath),  9*861  (Bergman).  Strong  pres- 
sure rather  diminishes  than  increases  the  density.  Bismuth 
melts  at  480°  (Crichton)  ;  at  507°  (Rudberg)  ;  at  509^ 
(Hermann) ;  and  expands  in  solidifying.  It  boils  at  an  inci- 
pient white  heat,  and  if  the  air  be  excluded,  sublimes  in 
laminae. 

Bismuth  forms  four  compounds  with  oxygen,  viz.,  the 
bioxide,  Bi02;  the  teroxide,  BiOg;  the  quadroxide  Bi04;  and 
bismuthic  acid,  BiOg. 

Bioxide  or  suboxide  of  ^i^mM^A.-— Bismuth  oxidises  slowly 
when  exposed  to  the  air  at  ordinary  temperatures,  becoming 
covered  with  a  brownish  film  of  suboxide.  When  heated  in 
the  air  till  it  fuses,  it  oxidates  more  rapidly,  becoming  covered 

S  4 


242  BISMUTH. 

with  the  same  brown  oxide,  which  is  renewed  as  often  as  it  is 
removed,  till  the  whole  of  the  metal  is  oxidised.  This  sub- 
oxide is  also  formed  when  subnitrate  of  bismuth  is  heated  with 
protochloride  of  tin.  By  pouring  a  hydrochloric  acid  solution 
of  equivalent  quantities  of  teroxide  of  bismuth  and  proto- 
chloride  of  tin  into  excess  of  moderately  strong  potash,  a 
black-brown  precipitate  is  formed,  consisting  of  a  lower  oxide  of 
bismuth  combined  with  stannic  acid ;  and  on  treating  this  com- 
pound  with  stronger  potash,  the  stannic  acid  dissolves  and  an 
oxide  of  bismuth  remains,  which,  when  dried  in  vacuo,  or  at 
100°,  out  of  contact  with  the  air,  forms  a  blackish-grey  crystal- 
line powder,  consisting  of  610.2,  retaining,  however,  a  small 
quantity  of  water.  It  shows  but  little  disposition  to  absorb 
oxygen  at  ordinary  temperatures,  but  when  heated,  it  is  instantly 
converted,  with  a  glimmering  light,  into  teroxide.  Acids  de- 
compose it  into  metallic  bismuth  and  teroxide.  AVhen  ignited 
in  an  atmosphere  of  carbonic  acid,  it  becomes  perfectly  anhy- 
drous, and  in  that  state  does  not  undergo  any  perceptible 
alteration  by  exposure  to  the  air  at  ordinary  temperatures,  and 
oxidises  but  slowly  even  at  a  red  heat  (R.  Schneider).* 

Teroxide  of  Bismuth,  BiOg  ;  237  or  3662-5.  —  Bismuth 
heated  in  the  air  till  it  boils,  takes  fire  and  bums  with  a 
faint  bluish  white  flame,  forming  teroxide  of  ])ismuth,  the 
vapour  of  which  condenses  on  the  surface  of  cold  bodies  in  the 
form  of  flowers  of  bismuth.  The  same  oxide  is  obtained  in 
solution  by  acting  on  bismuth  with  nitric  acid,  the  metal  being 
then  dissolved  with  evolution  of  nitrous  fumes.  Strong  sul- 
phuric acid  likewise  dissolves  it  at  a  boiling  heat,  with  evolution 
of  sulphurous  acid.  Hydrochloric  acid  acts  but  slightly  on 
it,  even  with  the  aid  of  heat.  Wlien  the  solution  of  the 
nitrate  is  mixed  with  water,  a  white  precipitate  of  subnitrate 
is  produced;  and  this,  when  gently  ignited,  yields  the  ter- 
oxide in  the  form  of  a  lemon-yellow  powder.     By  fusing  the 

*  Pogg.  Ann.  Ixxxviii.  45. 


OXIDES    OF    BISMUTH.  243 

hydrated  oxide  with  hydrate  of  potash,  or  boiling  it  with 
potash-ley,  the  anhydrous  oxide  may  be  obtained  in  yellow 
shining  needles.  Teroxide  of  bismuth  fuses  at  a  strong  red 
heat,  and  solidifies  in  a  crystalline  mass  on  cooling.  It  is 
easily  reduced  to  the  metallic  state  by  potassium  or  sodium 
at  a  gentle  heat,  and  by  charcoal  before  the  blowpipe. 

Teroxide  of  bismuth  combines  with  acids,  forming  salts 
which  are  very  heavy,  colourless,  unless  the  acid  itself  is 
coloured,  and  exert  a  poisonous  action.  Heated  on  charcoal 
with  carbonate  of  soda,  they  yield  a  button  of  metal.  ZinCf 
tin,  cadmium,  iron,  and  lead,  precipitate  the  metal  from  the  so- 
lutions of  these  salts.  Water  decomposes  most  bismuth-salts 
— provided  they  do  not  contain  too  large  an  excess  of  acid, 
throwing  down  a  sparingly  soluble  basic  salt,  while  the  acid 
remains  in  solution,  together  with  a  small  quantity  of  oxide. 
Hydrosulphuric  acid  produces  a  brown-black  precipitate  of 
tersulphide  of  bismuth,  insoluble  in  sulphide  of  ammonium. 
Caustic  alkalies,  at  ordinary  temperatures,  throw  down  the 
white  hydrated  oxide,  but  at  a  boiling  heat,  especially  if  they 
are  concentrated,  they  produce  a  yellow  precipitate  of  the 
anhydrous  oxide :  these  precipitates  are  insoluble  in  excess  of 
the  alkali.  Alkaline  carbonates  throw  down  a  white  preci- 
pitate of  carbonate  of  bismuth,  slightly  soluble  in  excess,  but 
precipitated  from  the  solution  by  a  caustic  alkali.  Chromate 
or  bichromate  of  potash  throws  down  a  yellow  chromate  of 
bismuth,  insoluble  in  caustic  potash,  whereby  it  is  distin- 
guished from  chromate  of  lead.  Sulphuric  acid  produces  no 
precipitate. 

Quadr oxide  of  bismuth,  Bi04. — When  a  bismuth-salt  con- 
tains free  chlorine,  caustic  potash  produces  in  it,  not  a  white 
but  a  yellow  precipitate,  which  consists  of  the  hydrate  of  a 
higher  oxide,  but  cannot  be  obtained  free  from  chlorine.  When 
this  yellow  hydrate  is  boiled  with  an  alkaline  chlorite  having 
a  strong  alkaline  reaction,  it  turns  brown,  like  peroxide  of  lead, 
and  is  converted  into  the  quadroxide  of  bismuth   (Arppe). 


244  BISMUTH. 

This  oxide  is  completely  dissolved  by  boiling  nitric  acid  ;  any 
yellow  or  green  residue  that  may  be  left,  consists  of  bismuthic 
acid.  It  is  perhaps  a  compound  of  teroxidc  of  bismuth  with 
bismuthic  acid :  BiOg'BiOg. 

Bismuthic  acid,  BiOg.  —  Prepared  by  passing  chlorine 
through  a  strong  solution  of  potash  in  which  finely  divided 
teroxide  of  bismuth  is  suspended  ;  also,  by  heating  a  mixture 
of  potash  and  teroxide  of  bismuth  for  a  long  time  in  contact 
with  the  air, — or  better,  by  calcining  a  mixture  of  teroxide  of 
bismuth,  caustic  potash,  and  chlorate  of  potash.  Bismuthic 
acid,  prepared  by  any  of  these  methods,  is  always  more  or  less 
mixed  with  teroxide  of  bismuth,  which,  however,  may  be  dis- 
solved out  by  weak  nitric  acid.  Bismuthic  acid  is  a  light  red 
powder,  which,  at  a  temperature  a  little  above  212°,  gives  off 
part  of  its  oxygen,  and  is  converted  into  quadroxide  of  bis- 
muth. Strong  acids  also  decompose  it,  reducing  it  to  the 
state  of  teroxidc  of  bismuth,  which  then  unites  with  the  acid. 
Bismuthic  acid  combines  with  potash,  and  forms  a  few  double 
salts,  whose  bases  are  the  alkali  and  teroxide  of  bismuth. 

Bisulphide  of  bismuth,  BiS2,  separates  in  crystals  from  a 
fused  mixture  of  metallic  bismuth  and  the  tersulphide,  and 
may  also  be  obtained  by  fusing  10  parts  of  bismuth  wnith 
3  parts  of  sulphur,  melting  the  resulting  mixture  three  times 
with  fresh  sulphur,  and  cooling  quickly.  Hydrochloric  acid 
decomposes  this  compound,  yielding  metallic  bismuth  and  the 
terchloride.  Hence,  and  jfrom  the  fact  that  its  crystalline 
form  is  the  same  as  that  of  the  tersulphide,  and  that  by 
fusing  the  tersulphide  with  metallic  bismuth,  in  certain  pro- 
portions, crystals  may  be  obtained  of  the  same  form  but 
containing  less  sulphur,  Schneider  concludes  that  the  sup- 
posed bisulphide  is  merely  a  mixture  of  the  tersulphide  with 
metallic  bismuth. 

Tersulphide  of  bismuth,  BiSg,  occurs  native  as  bismuth- 
glance,  and  may  be  formed  artificially  by  fusing  bismuth  with 


CHLORIDES    OF   BISMUTH.  245 

sulphur,  and  by  decomposing  bismuth-salts  with  hydrosul- 
phuric  acid»  The  native  variety  forms  right  rhombic  prisms, 
isomorphous  with  sulphide  of  antimony  :  its  colour  is  light 
lead-grey;  specific  gravity  from  6*4  to  6-5.  Tersulphide  of 
bismuth  is  decomposed  by  heat ;  the  native  sulphids,  heated 
in  a  tube,  yields  sublimed  sulphur ;  and  the  artificial  sulphide, 
when  fused  and  left  to  cool,  yields  globules  of  metallic  bismuth 
as  it  solidifies. 

Selenide  of  bismuth,  BiSe3,  is  obtained  by  melting  together 
1  eq.  of  bismuth  and  3  eq.  of  selenium,  and  remelting  the 
product  with  fresh  selenium  out  of  contact  with  the  air.  On  a 
recently  fractured  surface,  it  exhibits  a  steel-grey  colour,  me- 
tallic lustre,  and  a  distinct  crystalline  laminated  texture.  Its 
density  is  6*82;  hardness  equal  to  that  of  galena:  it  may  be 
readily  pulverised.  It  is  scarcely  attacked  by  hydrochloric 
acid,  but  nitric  acid  and  aqua  regia  decompose  it  readily 
(Schneider). 

Bichloride  of  bismuth,  BiCl2,  is  formed  by  the  action  of 
dry  hydrogen  on  the  terchloride  of  bismuth  and  ammonium, 
2NH4Cl.BiCl3,  at  about  570°,  or  by  heating  1  part  of  pul- 
verised bismuth  with  2  parts  of  subchloride  of  mercury  in  a 
sealed  tube,  at  about  460°,  and  purifying  the  product  by 
repeated  fusion  in  sealed  tubes.  It  is  a  black  hygroscopic 
mass,  which,  by  heating  in  the  air,  and  by  the  action  of  acids, 
is  resolved  into  metallic  bismuth  and  the  terchloride. 

Terchloride  of  bismuth,  BiClg. —  Pulverised  bismuth  thrown 
into  chlorine  gas  takes  fire  and  burns  with  a  pale  blue  light, 
forming  the  terchloride.  This  compound  may  also  be  ob- 
tained by  heating  1  part  of  bismuth  with  2  parts  of  proto- 
chloride  of  mercury,  or  by  evaporating  to  dryness  the  solution 
of  teroxide  of  bismuth  in  hydrochloric  acid,  and  distilling  the 
residue  out  of  contact  with  the  air.  It  is  a  white  opaque 
solid,  with  a  slight  tinge  of  brown  or  grey,  and  a  granular  frac- 
ture ;  melts  very  readily,  forming  an  oily  liquid.  The  hydrated 


246  BISMUTH. 

terchloride  is  obtained  in  crystals  by  dissolving  tlie  teroxide  in 
hydrochloric  acid,  and  evaporating.  The  anhydrous  chloride, 
the  crystals,  and  the  solution  are  decomposed  by  water,  yield- 
ing oxy chloride  of  bismuth,  BiClg  .  2Bi03,  in  the  form  of  an 
insoluble  white  powder,  commonly  known  as  pearl-white^ — 
and  hydrochloric  acid  holding  a  small  quantity  of  bismuth 
in  solution.  A  sulphochloHde,  of  analogous  composition, 
BiClg .  2BiS3,  is  obtained  by  heating  chloride  of  bismuth  and 
ammonium  with  sulphur  or  tersulphide  of  bismuth,  or  by 
passing  hydrosulphuric  acid  gas  over  the  same  compound, 
heated  to  a  temperature  between  485°  and  572°,  and  after- 
wards heating  the  product  to  its  melting  point  in  the  same 
gas:— 

SBiClg  -f  6HS  =  BiCla .  2BiS3  +  GIICl. 

The  product  of  either  of  these  operations,  after  being  waslied, 
first  with  water  containing  so  much  hydrochloric  acid  as  not 
to  give  a  precipitate  with  the  terchloride,  then  with  water 
slightly  acidulated,  and  lastly  with  pure  water,  forms  small, 
dark  grey,  crystalline  needles,  which,  when  heated  in  the  air, 
give  ofi*,  first,  chloride  of  bismuth,  then  sulphurous  acid, 
and  leave  a  mixture  of  oxychloride  and  basic  sulphate  of 
bismuth  (Schneider).  A  seleniochloride,  BiCl3 .  2BiSe3,  is 
obtained  by  adding  terselenide  of  bismuth  to  fused  chloride 
of  bismuth  and  ammonium.  It  forms  small  needle-shaped 
crystals,  having  a  dark  steel-grey  colour  and  metallic  lustre 
(Schneider). 

Terchloride  of  bismuth  and  ammonium.  —  A  solution  of 
1  eq.  of  terchloride  of  bismuth  and  2  eq.  of  sal-ammoniac, 
yields,  by  evaporation,  double  six-sided  pyramids  containing 
2NH4CI .  BiClg,  isomorphous  with  the  corresponding  ter- 
chloride of  antimony  and  ammonium  ( Jacquelain) .  A  solution 
of  1  eq.  terchloride  of  bismuth  and  6  eq.  sal-ammoniac  yields 
rhombic  crystals,  containing  3NH^C1 .  BiClg  (Arppe). 


SALTS    OF    BISMUTH.  247 

Bismuth  dissolves  in  a  boiling  solution  of  protochloride  of 
copper,  the  liquid  being  decolorised_,  and  appearing  to  con- 
tain the  compound,  3CU2CI.  BiClg.  Bismuth  dissolves  in  a 
similar  manner  in  other  cupric  salts  (Schneider). 

Teriodide  of  bismuth,  Bilg.  —  Obtained  as  a  crystalline 
sublimate  by  heating  1  eq.  (32  parts)  of  tersulphide  of  bis- 
muth with  3  eq.  (475  parts)  of  iodine.  Large,  thin,  crystal- 
line laminae,  having  the  form  of  regular  six-sided  prisms, 
of  a  blackish  grey  colour  with  a  tinge  of  brown  and  a 
strong  lustre.  The  compound,  heated  in  the  air,  volatilises 
for  the  most  part,  leaving  a  small  quantity  of  basic  oxide  of 
bismuth  of  a  red-brown  colour.  Boiling  water  converts  it 
into  the  same  compound.  Aqueous  potash  decomposes  it, 
forming  iodate  of  bismuth,  BiOg  .  3IO3 :  the  same  change  is 
more  slowly  produced  by  alkaline  carbonates.  Alkaline  sul- 
phides decompose  it,  forming  tersulphide  of  bismuth.  Hydro- 
chloric acid  dissolves  it  without  decomposition ;  nitric  acid, 
with  separation  of  iodine. 

Sulphates  of  bismuth. — When  bismuth  is  heated  with 
strong  sulphuric  acid,  sulphurous  acid  is  evolved,  and  the 
metal  is  converted  into  a  white  insoluble  powder,  consisting 
of  ter sulphate  of  bismuth,  Bi03  .  3SO3,  which  is  decomposed 
by  water,  yielding  a  very  acid  salt  which  dissolves,  and  a 
monobasic  sulphate,  Bi03  .  SO3  +  HO,  which  remains.  There 
is  also  a  bisulphate  of  bism,uth,  which  is  obtained  in  small 
delicate  needles  when  an  acid  solution  of  nitrate  of  bismuth 
is  mixed  with  sulphuric  acid  (Heintz). 

Carbonate  of  bismuth,  Bi03 .  CO2,  is  obtained  by  adding 
nitrate  of  bismuth  to  the  solution  of  an  alkaline  carbonate  : 
this  salt  is  used  in  medicine. 

Nitrates  of  bismuth.  —  The  neutral  or  ternitrate, 
Bi03.  3NO5+  lOHO,  is  obtained  by  dissolving  bismuth  in  hot 
nitric  acid,  evaporating  the  solution,  and  leaving  it  to  cool. 
The  salt  then  separates  in  transparent  oblique  prisms  of  six 
or  eight  sides,  and  tenninated  with  several  faces.      At  212° 


218  BISMUTH. 

they  separate  into  a  solid  and  a  liquid  portion,  the  latter 
solidifying  as  it  cools.  At  302°,  they  are  reduced  to  the 
mononitrate,  BiOg  .  NO5  +  HO ;  which,  when  further  heated 
to  500°,  gives  up  all  its  acid  and  water,  and  leaves  oxide  of 
bismuth. 

Siibnitrates  of  bismuth. — a.  Ternitrate  of  bismuth  dissolves 
without  decomposition  in  a  sfnall  quantity  of  water,  especially 
if  a  few  drops  of  nitric  acid  are  added.  But  a  larger  quan- 
tity of  water  decomposes  it,  forming  a  white  precipitate  of  a 
subsalt,  commonly  called  magistery  of  bismuth.  This  sub- 
stance is  generally  regarded  as  a  mononitrate  containing 
one  atom  of  water,  Bi03 .  NO5  +  HO ;  but,  according  to 
Becker  *,  the  basic  nitrate  obtained  directly  by  treating  the 
ternitrate  with  cold  water,  consists  of  BiOa .  NO5  +  2  HO. 
This  precipitate,  when  recently  formed,  dissolves  somewhat 
freely  in  water,  especially  if  the  water  contains  nitric  acid. 
Hence,  if,  after  the  precipitation  of  the  basic  salt,  the  super- 
natant liquid  be  mixed  with  a  large  quantity  of  water,  the 
precipitate  is  completely  redissolved;  but  after  a  while,  a 
basic  salt  separates,  containing  SBiOg .  4N05-}-9Aq ;  this, 
according  to  Becker,  is  the  tnie  magistery  of  bismuth, 
inasmuch  as,  in  the  usual  mode  of  preparing  that  sub- 
stance, the  same  change  takes  place  in  washing  the  precipitate. 
Boiling  water  decomposes  this  salt,  extracting  all  the  nitric 
acid,  excepting  about  1  per  cent.  —  b.  A  salt  containing 
5Bi03.4N05-f-12HO,  is  obtained  by  evaporating  a  solution 
of  the  ternitrate  at  a  strong  heat.  When  the  precipitate  first 
obtained  by  the  action  of  cold  water  on  a  solution  of  the  ter- 
nitrate is  heated  in  contact  with  a  free  acid,  or  when  the  same 
acid  solution  is  poured  into  hot  water,  a  -s^hite,  very  loose 
powder  is  precipitated,  containing  GBiOg  .  oNOg  +  9H0.  This 
salt  is  decomposed  by  water  more  readily  than  the  preceding. 
If  it  be  washed  with  water  as  long  as  the  filtrate  continues  to 

*  Arcliir.  riiarni.  Iv.  31.  and  129. 


SALTS    OF    BISMUTH.  249 

exhibit  a  strong  acid  reaction_,  a  crystalline  residue  is  left  on 
the  filter,  containing  4Bi03  •  ^^^5  •  9-A.q.  Duflos  obtained  a 
magistery  of  bismuth  having  the  same  composition,  by  treat- 
ing the  crystals  of  the  neutral  nitrate  with  24  times  their 
weight  of  water.  Lastly,  if  the  mononitrate,  completely  freed 
from  the  adhering  acid  liquid,  be  treated  with  water  likewise 
free  from  acid,  it  dissolves  completely ;  but  the  liquid  after  a 
while  becomes  milky,  and  after  long  standing  deposits  a 
white  amorphous  powder,  containing  SBiOg  .  SNOg  +  8HO. 
This  salt  may  be  formed,  in  addition  to  the  true  magistery  of 
bismuth,  if,  in  the  preparation,  of  that  substance,  too  large  a 
quantity  of  water  be  used,  and  the  greater  part  of  the  acid 
liquid  removed  (Becker.)  Magistery  of  bismuth  is  used  as 
a  cosmetic,  but  has  the  serious  disadvantage  of  being  black- 
ened by  hydrosulphuric  acid. 

Bichromate  of  bismuth,  BiOg  .  2Cr03. — When  a  solution 
of  ternitrate  of  bismuth,  containing  as  little  free  acid  as 
possible,  is  poured  into  a  moderately  concentrated  solution  of 
bichromate  of  potash,  bichromate  of  bismuth  is  obtained  in 
the  form  of  a  yellow  flocculent  precipitate,  which  becomes 
dense  and  crystalline  after  a  while,  or  immediately  if  heated. 
It  may  be  dried  without  decomposition  between  212°  and 
257°,  but  becomes  blackish- green  at  a  red  heat.  It  contains 
69'48  per  cent,  of  teroxide  of  bismuth  (J.  Lowe.) 

The  alloys  of  bismuth  are  remarkable  for  their  fusibility. 
The  amalgam  of  this  metal  is  liquid.  An  alloy  of  8  parts 
bismuth,  5  lead,  and  3  tin,  melts  at  202°  j  another  mixtui-e  of 
2  bismuth,  1  lead,  and  1  tin,  at  200*75° ;  these  mixtures  are 
known  by  the  name  of  fusible  metal.  Bismuth  is  also  added 
to  the  alloy  of  tin  and  lead  used  for  casting  stereotype  plates. 
Besides  increased  fusibility,  bismuth  communicates  to  this 
alloy  the  property  of  expanding  on  becoming  solid,  by  which 
it  is  rendered  capable  of  taking  an  accurate  impression. 


250  BISMUTH. 

ESTIMATION    OF    BISMUTH^     AND     METHODS     OF     SEPARATING     IT 
PROM    THE    PRECEDING    METALS. 

The  best  reagent  for  precipitating  bismuth  from  its  solu- 
tions is  carbonate  of  ammonia ;  which,  when  added  in  excess, 
throws  down  the  bismuth  completely :  the  liquid  must,  how- 
ever, be  left  to  stand  for  some  hours  in  a  warm  place,  other- 
wise a  considerable  quantity  of  the  bismuth  w  ill  remain  in 
solution.  The  precipitate,  after  being  washed  and  dried, 
must  be  separated  from  the  filter  as  completely  as  possible, 
the  filter  separately  burned,  and  the  precipitate  ignited  in  a 
porcelain  crucible  :  a  platinum  crucible  would  be  attacked  by 
it :  after  ignition,  it  consists  of  teroxide  of  bismuth  contain- 
ing 89'66  per  cent,  of  the  metal. 

If  the  solution  contains  hydrochloric  acid,  the  bismuth 
cannot  be  estimated  by  precipitation  with  carbonate  of  am- 
monia, or  any  other  alkali,  because  the  precipitate  so  pro- 
duced would  contain  oxychloride  of  bismuth  (p.  255).  In 
this  case,  therefore,  the  bismuth  must  be  precipitated  by 
hydrosulphuric  acid;  the  sulphide  of  bismuth  oxidised  and 
dissolved  by  nitric  acid ;  and  the  diluted  solution  treated  with 
carbonate  of  ammonia,  as  above. 

Bismuth  is  separated  from  the  alkalies  and  earths,  and 
from  iron,  cobalt,  nickel,  zinc,  and  chromium ,  hy  hydrosul- 
phuric acid ;  from  tin,  arsenic,  and  antimony,  by  sulphide  of 
ammonium ;  from  lead,  by  sidphuric  acid ;  and  from  copper 
and  cadminni  by  ammonia.  The  separation  of  bismuth  from 
cadmium  may  also  be  effected  by  cyanide  of  potassium, 
which  dissolves  the  latter  as  cyanide  of  cadmium  and  potas- 
sium, and  precipitates  the  bismuth.  The  precipitated  bis- 
muth, however,  always  contains  potash,  and  must  therefore 
be  dissolved  in  nitric  acid  and  precipitated  by  carbonate  of 
ammonia.  These  two  metals  may  also  be  separated  by 
means  of  bichromate  of  potash,  which  throws  down  the  bis- 
muth as  Bi03 .  2  Cr03,  and  retains  the  cadmium  in  solution. 


URANIUM.  251 


ORDEE   VII. 

METALS    NOT     INCLUDED    IN    THE    EOEE GOING    CLASSES, 
WHOSE   OXIDES  AEE  NOT  EEDUCED   BY  HEAT  ALONE. 


SECTION    L 

URANIUM. 

Eq.   60,  or  750;    U. 

This  metal  is  obtained  from  pitchblende,  a  mineral  con- 
taining from  40  to  95  per  cent,  of  uranoso-uranic  oxide, 
U3O4,  associated  witli  sulphur,  arsenic,  lead,  iron,  and  several 
otlier  metals.  The  mineral  is  finely  pounded ;  freed  by  elu- 
triation  from  the  finer  earthy  impurities ;  roasted  for  a  short 
time,  to  remove  part  of  the  sulphur  and  arsenic ;  then  dissolved 
in  nitric  acid,  and  the  solution  evaporated  to  dryness.  The 
residue  is  exhausted  with  water ;  the  solution  filtered  from  the 
brick-red  residue  of  ferric  oxide,  ferric  arseniate,  and  lead- 
sulphate  ;  the  greenish  yellow  filtrate  slightly  concentrated  by 
evaporation,  and  left  to  cool,  whereupon  it  deposits  crystals ; 
and  the  resulting  radiated  mass  of  crystallised  uranic  nitrate 
drained  on  a  funnel,  and  then  washed  with  a  small  quantity 
of  cold  water.  As  the  water  dissolves  a  portion  of  the  crystals, 
it  is  used  in  a  subsequent  operation  to  redissolve  the  residue 
obtained  by  evaporating  the  solution  of  pitchblende  in  nitric 
acid.  The  uranic  nitrate,  after  being  dried  in  the  air,  is 
introduced  into  a  wide-mouthed  bottle  containing  ether,  in 
which  it  immediately  dissolves ;  the  yellow  solution  is  left  to 
evaporate  in  the  air ;  and  the  resulting  crystals  are  purified 

VOL.  II.  T 


252  URANIUM. 

by  solution  in  hot  water  and  recrystallisation.  The  mixed 
mother-liquids,  after  dilution  with  water,  are  treated  with 
hydrosulphuric  acid  to  precipitate  arsenic,  lead,  and  copper, 
and  the  filtrate  is  freed  from  oxide  of  iron  by  evaporating  to 
dryness  and  digesting  the  residue  in  water.  The  solution 
thus  obtained  yields  a  fresh  crop  of  crystals  of  uranic  nitrate. 
This  salt  is  converted  by  ignition  into  uranoso-uranic  oxide, 
U3O4,  and  from  this  the  protoxide  is  obtained  by  ignition 
with  reducing  agents  (Peligot). 

Metallic  uranium  is  obtained  by  decomposing  the  proto- 
chloride  with  potassium  or  sodium.  If  the  mixture  be  heated 
in  a  platinum  crucible  over  a  spirit-lamp,  and  the  soluble 
alkaline  chloride  washed  out  by  water,  the  m'anium  is  ob- 
tained in  the  form  of  a  black  powder,  or  sometimes  aggre- 
gated on  the  sides  of  the  crucible  in  small  plates,  having  a 
silvery  lustre  and  a  certain  degree  of  malleability.  But,  by 
introducing  into  a  porcelain  crucible,  first,  a  layer  of  sodium, 
then  chloride  of  potassium,  and  then  a  mixture  of  chloride 
of  potassium  and  protochloride  of  uranium  (the  use  of  the 
chloride  of  potassium  being  to  moderate  the  action,  which  is 
otherwise  very  violent),  placing  the  porcelain  crucible  within 
a  closed  earthen  crucible  lined  with  charcoal,  and  heating 
it,  first  moderately,  till  the  reduction  takes  place,  and  then 
strongly  in  a  blast-furnace  for  15  or  20  minutes,  the  metal 
is  obtained  in  fused  globules  (Peligot). 

Uranium,  in  its  compact  state,  is  somewhat  malleable  and 
hard,  but  is  scratched  by  steel.  Its  specific  gravity  is  18*4 ; 
its  colour  is  like  that  of  nickel  or  iron.  When  exposed  to 
the  air,  it  soon  tarnishes  and  assumes  a  yellowish  colour.  At 
a  red  heat  it  oxidises  with  vivid  incandescence,  and  becomes 
covered  with  a  bulky  layer  of  black  oxide,  which  protects  the 
interior  from  oxidation.  In  the  pulverulent  state,  it  takes 
fire  at  about  402°,  burning  with  great  splendour,  and  forming 
a  dark-green  oxide.  It  is  permanent  in  the  air  at  ordi- 
nary  temperatures,    and  does  not    decompose    cold   water. 


OXIDES    OP   URANIUM.  253 

It  dissolves  with  evolution  of  hydrogen  in  dilute  acids, 
forming  green  solutions.  It  combines  directly  with  chlorine, 
giving  out  great  light  and  heat,  and  forming  a  green  vola- 
tile chloride.  It  unites  directly  with  sulphur  at  a  slightly 
elevated  temperature  (Peligot). 

Uranium  forms  four  compounds  with  oxygen,  viz.,  the 
protoxide,  UO ;  the  sesquioxidej  U2O3 ;  and  two  intermediate 
oxides,  U4O5,  and,  U3O4,  which  may  be  regarded  as  com- 
pounds of  the  other  two,  viz.,  2UO.U203and  UO.U2O3. 

Protoxide  of  uranium ;  Uranous  oxide,  UO,  68,  or  850. — 
This  oxide  is  obtained  by  exposing  uranoso-uranic  oxide,  mixed 
with  charcoal  powder,  bullock^s  blood,  or  oil,  to  the  strongest 
heat  of  a  blast-furnace ;  by  heating  the  same  oxide  to  redness 
in  a  current  of  dry  hydrogen ;  by  igniting  uranic  oxalate  out 
of  contact  of  air,  or  better,  in  a  current  of  hydrogen ;  or  by 
igniting  the  chloride  of  uranyl  and  potassium  (p.  257),  either 
alone  or  in  a  current  of  hydrogen.  Protoxide  of  uranium 
has  sometimes  the  form  of  an  earthy  powder  of  a  grey  or 
brown  colour ;  sometimes  of  crystalline  scales  having  the  me- 
tallic lustre.  It  was  for  a  long  time  regarded  as  metallic 
uranium,*  till  Peligot  f  pointed  out  its  true  nature,  and  ob- 
tained the  real  metal  in  the  manner  above  mentioned. 

Uranous  oxide,  after  ignition,  is  insoluble  in  boiling  dilute 
hydrochloric  or  sulphuric  acid,  but  dissolves  in  strong  sul- 
phuric acid.  The  hydrated  oxide  dissolves  readily  in  acids. 
Solutions  of  uranous  salts  are  green,  and,  when  treated  with 
alkalies  or  alkaline  carbonates,  or  with  carbonate  of  lime, 
yield  a  reddish-brown  gelatinous  hydrate  of  uranous  oxide, 
which  dissolves  in  alkaline  carbonates,  especially  in  carbonate 
of  ammonia,  forming  a  green  solution.  Alkaline  hydrosul- 
phates  yield  a  black  precipitate  of  uranous  sulphide.  Uranous 
salts  are  converted  into  uranic  salts  by  exposure  to  the  air,  by 

*  See  the  first  edition  of  this  work,  page  643. 
t  Ann.  Ch.  Phys.  [3,],  v.  5. ;  and  xii.  258. 

T  2 


254  URANIUM. 

the  action  of  nitric  acid,  and  by  gold  and  silver  salts;  the 
action  in  the  last  case  being  accompanied  by  precipitation  of 
metallic  gold  or  silver. 

Protochloride  of  uranium ;  Uranous  chloride,  UCl,  is  ob- 
tained by  burning  uranium  in  chlorine  gas,  or  by  passing 
that  gas  over  an  intimate  mixture  of  charcoal  and  either  of 
the  oxides  of  uranium,  strongly  heated  in  a  tube  of  very 
refractory  glass.  It  crystallises  in  dark-green  regular  octohe- 
drons,  which  have  a  metallic  lustre,  and,  when  heated  to  red- 
ness, volatilise  in  red  vapours  and  form  a  sublimate.  It  fumes 
strongly  on  exposure  to  the  air,  and  dissolves  very  readily  in 
water,  forming  a  green  solution. 

Uranous  sulphate,  UO.SO3,  is  found  native  as  uranium,' 
vitriol,  and  may  be  formed  artificially  by  dissolving  uranoso- 
uranic  oxide  in  boiling  oil  of  vitriol;  or  hydrated  uranous 
oxide  in  dilute  sulphuric  acid ;  or  by  decomposing  a  con- 
centrated solution  of  uranous  chloride  with  sulphuric  acid. 
Crystallises  with  two  and  with  four  atoms  of  water.  A  bibasic 
uranous  sulphate  is  obtained  by  treating  the  normal  salt  with 
a  large  quantity  of  water ;  by  exposing  the  alcoholic  solution 
of  that  salt  to  the  sun*s  rays ;  by  careful  addition  of  ammonia 
to  its  aqueous  solution ;  and  by  boiling  that  solution  with 
green  uranoso-uranic  oxide.  It  forms  a  light-green  powder 
haviug  a  silky  lustre. 

Uranoso-uranic  oxide,  U3O4,  or  UO.UjOg. —  This  oxide 
forms  the  principal  constituent  of  pitchblende.  It  is  obtained 
artificially  by  burning  the  metal  or  the  protoxide  in  the  air ; 
by  heating  the  protoxide  to  redness  in  an  atmosphere  of 
aqueous  vapour ;  and  by  gentle  ignition  of  uranic  oxide  or 
uranic  nitrate.  It  is  a  dark-green  powder  which  dissolves  in 
acids,  forming  green  solutions,  exhibiting  characters  inter- 
mediate between  those  of  uranous  and  uranic  salts,  and 
probably  consisting  of  mere  mixtures  of  the  two. 

Another  intermediate  oxide,  U4O5,  or  2UO.U2O3,  is  said 
to  be  formed  by  strongly  igniting  the  last  oxide  or  the  sesqui- 


URANIC    SALTS.  255 

oxide.     It  is  black,  and  dissolves  in  acids,  like  the  last ;  but 
it  is  probably  a  mere  mixture  of  U3O4  with  the  protoxide. 

Sesquioxide  of  uranium ;  Uranic  oxide^  ^2^3  ^  -^^^  ^^  1800. 
— Uranium  and  its  lower  oxides  dissolve  in  nitric  acid,  with 
evolution  of  nitric  oxide  and  formation  of  uranic  nitrate. 
When  a  solution  of  this  salt  in  absolute  alcohol  is  evaporated 
at  a  gentle  heat,  till  nitrous  ether  begins  to  escape,  an  orange- 
yellow  spongy  mass  is  obtained,  consisting  of  hydrated  uranic 
oxide  mixed  with  undecomposed  nitrate  :  the  nitrate  may  be 
dissolved  out  by  water,  and  the  hydrated  oxide  then  remains, 
exhibiting  a  lemon-yellow  or  orange-yellow  colour.  This 
hydrate  is  permanent  in  the  air,  and  does  not  absorb  carbonic 
acid.  At  572°,  it  yields  anhydrous  uranic  oxide,  which  is 
also  yellow ;  and  at  a  low  red  heat,  it  is  converted  into  green 
uranoso-uranic  oxide. 

The  uranic  salts  are  obtained  by  oxidising  uranous  or 
uranoso-uranic  salts  with  nitric  acid,  or  by  exposing  them  to 
the  air.  Most  of  them  contain  one  equivalent  of  uranic  oxide 
combined  with  one  equivalent  of  an  acid.  Now,  as  this  is  con- 
trary to  the  usual  analogy  of  the  normal  salts  of  sesquioxides, 
most  of  which  contain  three  equivalents  of  acid  to  one  equiva- 
lent of  base,  e.g.,  ferric  sulphate  =  Fe203  .  3SO3  j  sulphate  of 
alumina= AI2O3  .  3SO3, — Peligot  is  of  opinion  that  the  base  of 
these  salts  is  not  really  a  sesquioxide,  but  the  protoxide  of  a 
compound  radical  uranyl,  U2O2,  made  up  of  the  elements  of 
2  equivalents  of  uranous  oxide  :  1X203=  (U2O2)  O.  To  abbre- 
viate the  formulae,  we  shall  denote  the  compound  radical,  uranyl, 
by  the  symbol  U' ;  we  have  then  for  the  formula  of  uranic 
sulphate  :  U2O3  .  SO3  =  (U2O2)  O  .  SO3  =  U'O  .  SO3. 

Uranic  salts  are  yellow;  they  are  mostly  soluble  in  water, 
and,  in  solution,  have  a  very  rough  taste,  without  any  metallic 
after-taste.  They  are  reduced  to  uranous  salts  by  hydrosuU 
phuric  acid ;  also  by  alcohol  or  ether ,  in  sunshine.  Caustic 
alkalies  added  to  uranic  solutions  throw  down  a  yellow  preci- 
pitate, consisting  of  a  uranate  of  the  alkali,  which  is  insoluble 

T  3 


256  URANIUM. 

in  excess  of  the  reagent.  Alkaline  carbonates  produce  a 
yellow  precipitate,  consisting  of  a  carbonate  of  nrauic  oxide 
and  the  alkali,  soluble  in  excess,  especially  in  bicarbonate 
of  potash  or  sesquicarbonate  of  ammonia.  Potash  added  to 
these  solutions  throws  down  all  the  uranic  oxide.  From  the 
solution  in  carbonate  of  ammonia,  the  uranic  oxide  is  like- 
wise precipitated  by  boiling.  Carbonate  of  baryta  precipitates 
uranic  oxide  completely  from  its  solutions  at  ordinary  tem- 
peratures. Phosphate  of  soda,  added  to  uranic  salts  not 
containing  too  much  free  acid,  produces  a  white  precipitate 
of  uranic  phosphate,  having  a  sliglit  tinge  of  yellow.  Sulphide 
of  ammonium  produces  a  black  precipitate  of  uranic  sulphide, 
which  remains  for  a  long  time  suspended  in  the  liquid.  Hy- 
drosulphuric  acid  produces  no  precipitate.  Ferrocyanide  of 
potassium  produces  a  dark  red-brown  precipitate;  ferriq/- 
anide  of  potassium,  none.  Metallic  zinc  does  not  precipitate 
uranium  in  the  metallic  state  from  uranic  solutions,  but,  after 
a  long  time,  produces  a  yellow  precipitate  of  uranic  oxide. 

Uranic  oxide  and  its  salts,  fused  with  phosphorus-salt  in 
the  outer  blowpipe  flame,  produce  a  clear  yellow  glass  which 
becomes  greenish  on  cooling.  In  the  inner  flame,  the  glass 
assumes  a  green  colour,  becoming  still  greener  when  cold. 
Similar  colours  with  borax.  The  oxides  of  uranium  are  not 
reduced  to  the  metallic  state  by  fusion  with  carbonate  of  soda 
on  charcoal.  Uranic  oxide  is  used  for  imparting  a  delicate 
yellow  tint  to  glass ;  the  glass  thus  coloured  is  called  canary 
glass. 

Chloride  of  uranyl,  U202C1=U'C1. — When  dry  chlorine 
gas  is  passed  over  uranous  oxide  at  a  red  heat,  the  tube  be- 
comes filled  with  an  orange-yellow  vapour  of  this  compound, 
which  solidifies  in  a  yellow  crystalline  mass,  easily  fusible, 
but  not  very  volatile.  Dissolved  in  water,  it  forms  hydrated 
chloride  of  uranyl,  or  hydrochlorate  of  uranic  oxide  : 

U2O2CI  +  HO  =  U2O3.  HCl. 


URANIC    PHOSPHATES.  257 

Chloride  of  uranyt  and  potassium,  KCl .  U  CI  +  2Aq.,  is 
formed  by  evaporating  an  aqueous  mixture  of  uranic  chloride 
and  chloride  of  potassium.  By  heating  the  hydrated  crystals 
to  212°,  the  anhydrous  compound  is  obtained. 

Uranic  sulphate;  sulphate  of  uranyl,  —  The  monosulphate 
V'O.SOg  +  SAq.  is  obtained  by  dissolving  uranoso-uranic 
oxide  in  strong  sulphuric  acid,  diluting  the  solution  with 
water,  and  oxidising  with  nitric  acid ;  also  by  decomposing  a 
solution  of  uranic  nitrate  with  sulphuric  acid,  expelling  the 
excess  of  acid  by  heat,  dissolving  the  residue  in  water,  evapo- 
rating the  solution  to  a  syrup,  and  leaving  it  to  crystallise. 
Forms  small  lemon-yellow  prisms.  According  to  Berzelius, 
a  bisulphate  and  a  tersulphate  are  obtained  by  dissolving  the 
monosulphate  in  sulphuric  acid;  but  Peligot  denies  their 
existence.  A  basic  sulphate  is  found  native  in  the  form  of  a 
yellow  powder.  The  monosulphate  forms,  with  sulphate  of 
potash,  a  crystalline  double  salt,  whose  formula  is : 

KO .  SO3  +  U2O3 .  SO3  +  2H0  =  ^,  I  2SO4  +  2H0. 

Uranic  nitrate ;  nitrate  of  uranyl ;  U203.N05  =  U'O.N05, 
is  formed  by  treating  the  metal  or  either  of  its  oxides  with 
nitric  acid.  It  crystallises  in  lemon-yellow  prisms.  The 
solution  of  this  salt  possesses  the  power  of  lowering  the  re- 
frangibility  of  rays  of  light  which  fall  upon  it,  producing  the 
peculiar  phenomenon  called  fluorescence.  This  property  is 
likewise  exhibited  by  other  compounds  of  uranium,  especially 
by  canary-glass.  A  basic  nitrate  is  formed  by  gently  igniting 
the  normal  salt. 

Uranic  phosphates ;  phosphates  of  uranyl. — Three  of  these 
salts  are  known,  all  containing  3  atoms  of  base  to  1  atom  of 
acid.  When  uranic  oxide  is  digested  in  a  small  quantity  of 
aqueous  phosphoric  acid,  a  yellow  saline  mass  is  produced, 
part  of  which  dissolves  in  boiling  water,  leaving  a  light  yellow 
powder,  which  is  the  neutral  phosphate  (2U'0  .  HO) .  PO5. 
The  aqueous   solution  concentrated  by  heat,  and  then  left 

T  4 


258  URANIUM. 

to  evaporate  in  vacuo  over  oil  of  vitriol,  deposits  a  lernon- 
yellow  crystalline  salt,  consisting  of  the  acid  phosphate 
(U'O  .  2H0) .  PO5.  The  basic  phosphate  has  not  been  ob- 
tained in  the  separate  state ;  but  when  uranic  nitrate  is 
mixed  with  a  moderate  excess  of  basic  phosphate  of  soda 
(3NaO .  PO5),  a  dark  yellow  precipitate  is  formed  containing 
(Na0.2U'0)  .  PO5  +  3U'0  .  PO5  (Wertheim)  *  When 
uranic  acetate  is  added  to  a  solution  of  any  soluble  phosphate 
containing  an  abundance  of  ammonia  and  free  acetic  acid,  a 
yellow  precipitate  is  formed  consisting  of  ammonio-uranic 
phosphate,  2U'0 .  NH4O.PO5,  which,  when  ignited,  leaves 
iiranic  pyrophosphate,  2U'0  .  PO5.  This  reaction  affords  a 
ready  and  exact  method  of  estimating  phosphoric  acid.  The 
insoluble  phosphates,  even  those  of  alumina  and  sesquioxide 
of  iron,  are  also  decomposed  by  boiling  with  uranic  acetate 
in  presence  of  a  large  excess  of  acetate  of  ammonia  and 
free  acetic  acid,  the  bases  dissolving,  while  the  phosphoric 
remains  undissolved  in  the  form  of  the  ammonio-uranic 
phosphate  above  described.  To  separate  phosphoric  acid 
from  iron  in  this  manner  requires,  however,  a  very  large 
excess  of  the  uranium-salt  (W.  Knop).t 

A  neutral  and  an  acid  arseniate  of  uramjlj  analogous  in 
composition  to  the  phospliatcs,  have  also  been  obtained  by 
similar  means.  The  composition  of  these  phosphates  and 
arseniates  affords  a  strong  argument  in  favour  of  the  uranyl 
theory. 

Compounds  of  uranic  oxide  with  bases,  —  Uranic  oxide 
combines  as  an  acid  with  the  alkalies,  earths,  and  other  me- 
tallic oxides,  forming  salts  which  may  be  called  uranates. 
The  uranates  of  the  alkalies  are  obtained  by  precipitating  a 
solution  of  uranic  oxide  in  an  acid  with  an  alkali;  the 
uranates  of  the  earths  and  heavy  metallic  oxides,  by  adding 
ammonia  to  a  solution  of  an  uranic  salt  mixed  with  one  of 

*  J.  pr.  Chem.  xliii.  321.  f  Chem.  Gaz.  1856,  467. 


ESTIMATION    OF    URANIUM.  259 

these  bases.  The  uranates  are  for  the  most  part  yellow, 
and  after  ignition  orange-yellow.  The  soda-compound, 
NaO  .  2U2O3  -H  6H0,  is  used  for  colouring  glass,  and  is  pre- 
pared on  the  large  scale  by  roasting  pitchblende  with  lime-< 
stone  in  a  reverberatory  furnace;  treating  the  resulting  uranate 
of  lime  with  dilute  sulphuric  acid,  by  which  the  uranic  oxide 
is  almost  completely  dissolved ;  mixing  the  green  solution  with 
crude  carbonate  of  soda,  by  which  the  uranium  is  precipitated 
together  with  other  metals,  but  redissolved  tolerably  free  from 
impurities  by  excess  of  the  alkali;  and  treating  the  liquid 
with  dilute  sulphuric  acid  as  long  as  effervescence  is  produced. 
The  uranate  of  soda  is  then  precipitated  in  a  form  well 
adapted  for  the  manufacture  of  yellow  glass. 

ESTIMATION    OF    URANIUM,    AND    METHODS    OF    SEPARATING    IT 
FROM    THE    PRECEDING    METALS. 

Uranium  is  completely  precipitated  from  uranic  solutions 
by  ammonia.  The  precipitate,  which  consists  of  hydrated 
uranic  oxide  containing  ammonia,  must  be  washed  with  water 
containing  sal-ammoniac,  as  it  runs  through  the  filter  when 
washed  with  pure  water.  It  is  then  dried  and  ignited  in  an 
open  crucible,  whereby  it  is  converted  into  uranoso-uranic 
oxide,  U3O4 ;  but  to  obtain  a  perfectly  definite  result,  and 
prevent  further  oxidation  during  cooling,  it  is  necessary  to 
put  the  cover  on  the  crucible  while  the  substance  is  still  red- 
hot,  and  keep  it  there  till  the  crucible  is  quite  cold.  The 
oxide  thus  obtained  contains  84^*90  per  cent,  of  uranium. 
An  accurate  result  is  likewise  obtained  by  igniting  the  ses- 
quioxide  in  an  atmosphere  of  hydrogen,  whereby  it  is  reduced 
to  protoxide  containing  88*24  per  cent,  of  the  metal. 

If  the  uranic  solution  contains  a  considerable  quantity  of 
an  earth  or  a  fixed  alkali,  the  precipitate  formed  by  ammonia 
carries  down  with  it  a  certain  portion  of  the  earth  or  alkali ; 


260  URANIUM. 

to  free  it  from  which  it  must,  before  ignition,  be  redissolved 
in  hydrochloric  acid  and  reprecipitated  by  ammonia. 

From  the  fixed  alkalies,  uranium,  in  the  state  of  sesqui- 
oxide,  is  separated  by  ammonia,  attention  being  paid  to  the 
precaution  just  mentioned. 

From  batata  it  is  separated  by  sulphuric  acid ;  from  strontia 
and  limej  also  by  sulphuric  acid  with  addition  of  alcohol. 

From  magnesia,  manganese,  cobalt,  nickel,  and  zinc,  these 
metals  being  in  the  state  of  protoxide,  and  the  uranium  in  the 
state  of  sesquioxide,  it  is  separated  by  precipitation  with 
carbonate  of  baryta. 

Fi'om  iron  it  is  separated  by  carbonate  of  ammonia,  both 
metals  being  in  the  state  of  sesquioxide;  the  uranic  oxide 
then  dissolves,  while  the  ferric  oxide  remains  undissolved. 
Care  must,  however,  be  taken  that  the  carbonate  of  ammonia 
be  really  monocarbonate,  quite  free  from  excess  of  carbonic 
acid,  otherwise  the  iron  will  also  be  dissolved.  To  ensure 
this  condition,  the  carbonate  of  ammonia  must  be  previously 
boiled,  and  the  solution  of  the  oxides,  if  acid,  must  be 
neutralised  with  ammonia  till  a  slight  permanent  precipitate 
begins  to  form :  the  solution  should  then  be  diluted  with 
water.  The  uranic  oxide  is  separated  from  the  filtrate  either 
by  boiling,  or  by  supersaturation  with  hydrochloric  acid  and 
precipitation  by  ammonia. 

From  alumina,  uranium  is  also  separated  by  carbonate  of 
ammonia,  and  with  greater  facility. 

From  cadmium,  copper,  lead,  tin,  arsenic,  antimony,  and 
bismuth,  uranium  is  separated  by  hydrosulphuric  acid ;  from 
titanium  and  chromium  in  the  same  manner  as  iron  is  sepa- 
rated from  those  metals  (pp.  152.  171.) ;  and  from  vanadium, 
tungsten,  molybdenum,  and  tellurium,  by  sulphide  of  am- 
monium, in  which  the  sulphides  of  the  last  named  metals  are 
soluble. 


OXIDES    OF    CERIUM.  261 

SECTION   IL 

CERIUM. 

Eq.  47-26,  or  590*87.     Ce. 

This  metal,  wliich  was  discovered  in  1803,  simultaneously 
by  Klaproth,  and  by  Hisinger  and  Berzelius,  exists,  together 
with  lanthanum  and  didymium,  in  cerite,  allanite,  orthite, 
yttro-cerite,  and  a  few  other  minerals,  all  of  somewhat  rare 
occurrence.  The  most  abundant  of  them  is  cerite,  which 
is  a  compound  of  silicic  acid  with  the  oxides  of  cerium,  lan- 
thanum, and  didymium,  together  with  small  quantities  of 
lime  and  oxide  of  iron.  To  extract  the  oxides  of  the  three 
metals,  the  cerite  is  finely  pounded  and  boiled  for  some  hours 
with  strong  hydrochloric  acid,  or  aqua-regia,  which  dissolves 
the  metallic  oxides,  leaving  nothing  but  silica.  The  filtered 
solution  is  then  treated  with  a  slight  excess  of  ammonia, 
which  precipitates  everything  but  the  lime ;  the  precipitate  is 
redissolved  in  hydrochloric  acid,  and  the  solution  treated  with 
excess  of  oxalic  acid.  A  white  or  faintly  rose-coloured  preci- 
pitate is  then  obtained,  consisting  of  the  oxalates  of  cerium, 
lanthanum,  and  didymium :  it  is  curdy  at  first,  but  in  a  few 
minutes  becomes  crystalline,  and  easily  settles  down.  When 
dried  and  ignited,  it  yields  a  red-brown  powder,  containing 
the  three  metals  in  the  state  of  oxide.  The  finely  pounded 
cerite  may  also  be  mixed  with  strong  sulphuric  acid  to  the 
consistence  of  a  thick  paste,  the  mixture  gently  heated  till  it 
is  converted  into  a  dry  white  powder,  and  this  powder  heated 
somewhat  below  redness  in  an  earthen  crucible.  The  three 
metals  are  thus  brought  to  the  state  of  basic  sulphates,  which 
dissolve  completely  when  very  gradually  added  to  cold  water ; 
and  the  solution  treated  with  oxalic  acid  yields  a  precipitate 
of  the  mixed  oxalates,  which  may  be  ignited  as  before. 

From  the  red-brown  mixture  of  the  oxides  of  cerium,  lan- 
thanum, and  didymium  thus  obtained,  a  pure  oxide  of  cerium 


262  CERIUM. 

may  be  prepared  by  either  of  the  folloAving  processes  : — 1 .  The 
mixed  oxides  are  heated  with  strong  hydrochloric  acid,  which 
dissolves  the  whole,  with  evolution  of  chlorine ;  the  solution 
precipitated  with  excess  of  caustic  potash ;  and  chlorine  gas 
passed  through  the  liquid  with  the  precipitate  suspended  in 
it.  The  cerium  is  thereby  brought  to  the  state  of  sesqui- 
oxide,  which  is  left  undissolved  in  the  form  of  a  bright 
yellow  precipitate,  while  the  lanthanum  and  didymium  re- 
main in  the  state  of  protoxides,  and  dissolve.  To  ensure 
complete  separation,  the  passage  of  the  chlorine  must  be 
continued  till  the  liquid  is  completely  saturated  with  it,  and 
the  solution,  together  >vith  the  precipitate,  left  for  several 
hours  in  a  stoppered  bottle,  and  agitated  now  and  then.  The 
liquid  is  then  filtered,  the  washed  precipitate  treated  with 
strong  boiling  hydrochloric  acid,  which  dissolves  it  with  evo- 
lution of  chlorine,  and  forms  a  colourless  solution  of  proto- 
chloride  of  cerium ;  and  this,  when  treated  with  oxalic  acid 
or  oxalate  of  ammonia,  yields  a  perfectly  white  precipitate  of 
oxalate  of  cerium,  which  may  be  converted  into  oxide  by 
ignition  (Mosander).  2.  The  red-brown  mixture  of  the  three 
oxides  is  treated  with  very  dilute  nitric  acid  (I  part  of  nitric 
acid  of  ordinary  strength  to  between  50  and  100  parts  of 
water),  which  dissolves  the  greater  part  of  the  oxides  of  lan- 
thanum and  didymium,  and  leaves  the  oxide  of  t  erium ;  and 
by  treating  the  residue  with  very  strong  nitric  acid,  the  last 
traces  of  lanthanum  and  didymium  may  be  extracted  (Mo- 
sander, Marignac).  3.  The  red-brown  mixture  of  the  three 
oxides  is  boiled  for  several  hours  in  a  strong  solution  of 
chloride  of  ammonium.  The  oxides  of  lanthanum  and  didy- 
mium then  dissolve,  with  evolution  of  ammonia,  and  eerie  or 
ceroso-ceric  oxide  is  left  in  a  state  of  purity.  It  must  be 
collected  on  a  filter  and  washed  with  a  solution  of  sal-am- 
moniac, because,  when  washed  with  pure  water,  it  first  runs 
through  the  filter,  and  then  stops  it  up  (Watts).* 

»  Cbem.  Soc.  Qu.  J.  ii.  147. 


CEROUS    OXIDE.  263 

Metallic  cerium  is  obtained  by  heating  the  pure  anhydrous 
protochloride  with  potassium  or  sodium.  It  is  a  grey  powder 
which  acquires  the  metallic  lustre  by  pressure.  It  oxidises 
readily,  decomposes  water  slowly  at  ordinary  temperatures, 
quickly  at  the  boiling  heat,  and  dissolves  rapidly  in  dilute 
acids,  with  evolution  of  hydrogen,  forming  a  solution  of  a 
cerous  salt. 

Protoxide  of  cerium ;  Cerous  oxide,  CeO ;  55*26  or  690*8. — • 
This  oxide  is  scarcely  known  in  the  anhydrous  state.  The 
sesquioxide,  exposed  to  the  strongest  heat  of  a  wind-furnace, 
in  a  crucible  lined  with  charcoal,  yields  a  residue  chiefly  con- 
sisting of  protoxide,  but  the  reduction  is  never  complete. 
The  hydrated  protoxide  is  easily  obtained  by  precipitating 
the  chloride  with  a  caustic  alkali.  It  dissolves  readily  in 
acids,  forming  the  protosalts  of  cerium  or  cerous  salts,  the 
solutions  of  which  are  distinguished  by  the  following  cha- 
racters :  Caustic  potash  or  soda  produces  a  white  precipitate 
of  the  hydrated  protoxide,  which  is  insoluble  in  excess, 
and  is  converted  into  the  yellow  sesquioxide  by  the  action 
of  chlorine  or  hypochlorous  acid.  Ammonia  precipitates  a 
basic  salt.  Alkaline  carbonates  form  a  white  precipitate 
of  cerous  carbonate  insoluble  in  excess.  Oxalic  acid  or 
oxalate  of  ammonia  produces  a  white  precipitate  of  cerous 
oxalate,  gelatinous  at  first,  but  quickly  assuming  the  crystal- 
line character,  and  converted  by  ignition  in  an  open  vessel 
into  a  salmon-coloured  powder,  consisting  of  sesquioxide  of 
cerium  mixed  with  protoxide.  Hydrosulphuric  acid  produces 
no  precipitate.  Sulphide  of  ammonium  throws  down  the 
hydrated  protoxide.  Ferrocyanide  of  potassium  produces  a 
white  pulverulent  precipitate ;  ferricyanide  of  potassium,  none. 
Sulphate  of  potash  produces  a  white  crystalline  precipitate  of 
potassio-cerous  sulphate,  nearly  insoluble  in  pure  water,  and 
quite  insoluble  in  excess  of  sulphate  of  potash.  With  dilute 
solutions  the  precipitate  takes  some  time  to  form.  This  cha- 
racter, together  with  the  beha\4our  of  the  oxalate,  and  the 


2G4  CERIUM. 

yellow  coloration  of  the  hydrated  protoxide  by  cblonne,  serves 
to  distinguish  cerium  from  all  other  metals.  Cerous  salts 
in  solution  have  a  sweet  astringent  taste,  and  redden  litmus, 
even  when  tlie  acid  is  perfectly  saturated.  All  compounds  of 
cerium,  ignited  with  borax  or  phosphorus -salt  in  the  outer 
blowpipe-flame,  yield  a  glass  which  is  deep  red  while  hot,  but 
becomes  colourless  on  cooling.  In  the  inner  flame  a  colour- 
less bead  is  formed,  but  when  ignited  with  excess  of  oxide  of 
cerium,  it  forms  a  yellow  enamel. 

Sesquioxide  of  cerium;  Ceric  oxide,  Ce203. — It  is  doubtful 
whether  this  oxide  has  been  obtained  in  the  separate  state. 
The  hydrated  protoxide,  the  nitrate,  and  the  oxalate,  yield, 
when  ignited  in  the  acid,  a  salmon-coloured  powder,  which 
is  generally  regarded  as  ceric  oxide ;  but,  according  to 
Marignac,  it  is  a  mixture  or  compound  of  the  sesquioxide 
and  protoxide  of  cerium,  not  quite  constant  in  composition,  but 
containing  on  the  average  82*  15  percent  of  metal,  and  there- 
fore nearly  agreeing  with  the  formula  CCyOg  or  3Ce0.2Ce203. 
When  mixed  with  oxide  of  didymium,  its  colour  is  red- 
brown.  This  oxide  is  nearly  insoluble  in  strong  nitric  and 
hydrochloric  acids,  even  at  the  boiling  heat,  but  strong 
boiling  sulphuric  acid  dissolves  it.  Hydrochloric  acid,  with 
the  aid  of  reducing  agents,  such  as  alcohol,  dissolves  it  slowly 
at  the  boiling  heat,  forming  a  solution  of  cerous  chloride.  If 
mixed  with  the  oxide  of  lanthanum  or  didymium,  it  dissolves 
readily  in  strong  boiling  hydrochloric  acid,  with  evolution  of 
chlorine.  The  solution  of  this  oxide  in  strong  sulphuric  acid 
has  a  bright  yellow  colour,  and  deposits  yellow  prismatic  crys- 
tals, which,  according  to  Marignac,  consist  of  a  ceroso-ceric- 
sulphate,  containing  Ce^Og.  4S03-f  7H0.  Potash,  added  to 
the  solution  of  this  salt,  throws  down  a  yellow  hydrate,  which 
dissolves  readily  in  acids.  The  solutions  are  yellow,  and, 
when  boiled  with  hydrochloric  acid,  are  converted  into  cerous 
salts. 

Protosulphide  of  cerium,  CeS,  is  obtained  by  igniting  the 


SALTS    OF    CERIUM.  265 

carbonate  in  vapour  of  bisulphide  of  carbon,  or  by  heating 
an  oxide  of  cerium  with  sulphide  of  potassium.  The  first 
process  yields  a  light  powder  of  the  colour  of  red  lead ;  the 
second,  a  product  resembling  mosaic  gold.  The  sesquisulphide 
of  cerium  is  not  known  in  the  free  state,  but  exists  in  certain 
sulphur-salts. 

Protochloride  of  ceriunij  CeCl.  —  Cerium  burns  vividly 
when  heated  in  chlorine  gas,  and  forms  this  compound.  The 
anhydrous  chloride  may  be  prepared  by  igniting  the  sulphide, 
or  the  residue  obtained  by  evaporating  to  dryness  a  solution 
of  the  chloride  mixed  with  sal-ammoniac,  in  a  current  of 
chlorine  gas.  If  the  air  is  not  completely  excluded,  an 
oxychloride  is  also  produced.  The  anhydrous  chloride  is  a 
white  porous  mass,  fusible  at  a  red  heat,  and  perfectly  soluble 
in  water.  A  hydrated  chloride  is  obtained  in  colourless  four- 
sided  prisms,  by  dissolving  the  hydrated  oxide  or  the  car- 
bonate in  hydrochloric  acid,  and  evaporating  to  a  syrup. 
The  solution,  when  exposed  to  the  air,  turns  yellow,  from 
formation  of  a  eerie  salt. 

Sesquichloride  of  cerium. — The  hydrated  sesquioxide  dis- 
solves in  cold  hydrochloric  acid,  forming  a  red  solution,  which, 
however,  soon  gives  off  chlorine,  and  is  reduced,  more  or  less 
completely,  to  protochloride. 

Protofluoride  of  cerium  is  formed  by  precipitating  the  pro- 
tochloride with  an  alkaline  fluoride.  The  sesquifluoride  occurs 
native  in  six-sided  prisms,  mixed  with  half  its  weight  of 
protofluoride ;  also  with  the  fluorides  of  yttrium  and  calcium, 
in  yttrocerite.  An  oxyfluoride  of  cerium,  Ce4F303-|-3HO,  is 
also  found  native. 

Cerous  carbonate,  CeO  .  COg  +  SHO,  is  formed  by  exposing 
the  hydrated  protoxide  to  the  air,  or  by  precipitation. 

Cerous  oxalate,  0400203,  is  precipitated  from  cerous  salts 
by  oxalic  acid  or  oxalate  of  ammonia  added  in  excess,  even 
when  the  solution  contains  a  considerable  quantity  of  free  nitric 
or  hydrochloric  acid.     It  is  at  first  curdy,  but  soon  becomes 


266  CERIUM. 

very  dense  and  crystalline.  When  ignited  with  free  access  of 
air,  it  yields  ceroso-ccric  oxide. 

Cerous  sulphate^  CeO  .  SO3. — The  anhydrous  salt  is  a  white 
powder,  which,  when  sprinkled  with  a  small  quantity  of  water, 
becomes  very  hot,  and  condenses  into  a  solid  mass,  veiy  diffi- 
cult to  dissolve.  It  forms  two  crystallme  hydrates,  viz., 
2 (CeO  .  SO3)  +  3H0  and  (CeO  .  SO3)  +  3H0.  The  anliydrous 
salt,  heated  in  a  close  vessel,  leaves  a  basic  cerous  sulphate ; 
but,  with  free  contact  of  air,  it  leaves  a  basic  eerie  or  ceroso- 
ceric  sulphate.  Cerous  sulphate  forms  with  sulphate  of  potash 
a  crystalline  double  salt,  containing  CcO  .  SO3  +  KO  .  SO3, 
which  is  nearly  insoluble  in  water. 

Cerous  phosphate. — Obtained  by  precipitating  a  cerous  salt 
with  phosphate  of  soda.  It  also  occurs  native  (associated 
with  the  phosphates  of  lanthanum  and  didymiura),  in  several 
forms.  In  Monazite  and  Edwardsite,  it  occurs  in  oblique 
rhombic  prisms ;  in  the  former  it  is  associated  with  thorina, 
and  smaU  quantities  of  lime,  manganese,  and  tin;  in  the 
latter,  with  alumina,  zirconia,  and  silica.  Cryptolite  is  a 
tribasic  phosphate  of  cerium,  occurring  in  the  rose-coloured 
apatite  of  Arendal  in  Norway,  and  is  separated  by  dissolv- 
ing the  apatite  in  nitric  acid.  It  then  remains  in  the 
form  of  a  crystalline  powder,  appearing  under  the  micro- 
scope to  consist  of  hexagonal  prisms.  Sp.  gr.  4*6  (Wohler).* 
Phosphocerite  is  a  mineral  similar  in  composition  to  cryp- 
tolite. It  was  discovered  by  Mr.  O.  Sims  in  the  cobalt-ore 
of  Johannisberg  in  Sweden,  of  which  it  forms  about  one- 
thousandth  part.  It  remains  as  a  residual  product  when  the 
ore  after  calcination  is  treated  with  hydrochloric  acid  for  the 
purpose  of  extracting  the  cobalt.  It  is  a  greyish  yellow 
crystalline  powder,  mixed  with  a  small  quantity  of  minute 
dark  purple  crystals,  which  are  strongly  attracted  by  the 
magnet,  and  consist  chiefly  of  magnetic  oxide  of  iron.  The 
crystals  of  phosphocerite,  when  examined  by  the  microscope, 

»  Ann.  Ch.  Pharm.  Ivii.  268. 


ESTIMATION    OF    CERIUM.  267 

exhibit  two  forms,  one  an  octohedron,  the  other,  a  four-sided 
prism  with  quadrilateral  summits,  both  forms  apparently- 
belonging  to  the  right  prismatic  system.  Sp.  gr.  4-78.  The 
mineral  contains  64*68  per  cent,  protoxide  of  cerium,  &c., 
38-46  phosphoric  acid,  2*83  oxide  of  iron,  and  3*41  oxide  of 
cobalt,  silica,  &c.  It  is  very  rich  in  didymium.  Strong 
sulphuric  acid,  aided  by  gentle  heat,  decomposes  it,  forming 
a  pasty  mass,  which  dissolves  in  cold  water  with  the  exception 
of  a  small  quantity  of  silica   (Watts).* 


ESTIMATION    OF     CERIUM,     AND     METHODS    OP    SEPARATING    IT 
FROM    THE    PRECEDING    METALS. 

Cerium  is  precipitated  from  neutral  solutions  of  cerous 
salts  by  potash,  as  cerous  hydrate;  or  by  oxalate  of  am- 
monia, as  cerous  oxalate;  and  either  of  these  compounds  is 
converted  by  ignition  in  an  open  vessel  into  ceroso-ceric 
oxide.  This  oxide,  as  already  observed,  is  not  perfectly  de- 
finite in  constitution;  it  may  be  stated  approximately  to 
contain  96'5  per  cent,  of  cerous  oxide,  or  82"5  per  cent,  of 
the  metal,  and  this  estimate  may  be  adopted  where  great 
accuracy  is  not  required.  A  more  exact  method,  however,  is 
to  dissolve  the  hydrate  precipitated  by  potash  in  dilute  sul- 
phuric acid,  then  evaporate,  and  heat  the  residue  to  com- 
mencing redness,  whereby  it  is  converted  into  the  anhydrous 
sulphate  CeO  .  SO3,  containing  57*6  per  cent,  of  the  protoxide 
of  cerium,  or  49' 6  per  cent,  of  the  metal. 

Hydrosulphuric  acid  serves  to  separate  cerium  from  all 
metals  which  are  precipitated  by  that  reagent  from  their  acid 
solutions. 

From  manganese^  iron,  cobalt,  nickel,  zinc,  titanium, 
chromium,  vanadium,  and  tungsten,  cerium  may  be  separated 
by  means  of  a  saturated  solution  of  sulphate  of  potash. 

•  Chem.  Soc.  Qu.  J.,  ii.  131. 
VOL.  TI.  U 


268  LANTHANUM. 

From  alumina  it  may  be  separated  by  carbonate  of  baiyta, 
which  precipitates  alumina  and  not  cerous  oxide ;  from  ylucina 
by  sulphate  of  potash. 

From  yttria,  with  which  it  is  often  associated  in  minerals, 
it  is  separated  by  a  saturated  solution  of  sulphate  of  potash 
added  in  excess,  the  sulphate  of  yttria  and  potash  being 
soluble  in  excess  of  sulphate  of  potash,  while  the  cerous  double 
salt  remains  undissolved. 

From  zirconia,  cerium  is  separated  by  treating  the  boihng 
acid  solution  with  sulphate  of  potash,  whereby  the  greater 
part  of  the  zirconia  is  precipitated  as  basic  sulphate,  while 
the  cerium  remains  dissolved ;  to  complete  the  precipitation, 
a  small  quantity  of  ammonia  must  be  added,  but  not  sufficient 
to  saturate  the  acid  (H.  Rose). 

From  magnesia  also  cerium  may  be  separated  by  sulphate 
of  potash;  from  baryta,  strontia,  and  lime,  it  is  separated 
by  ammonia  added  in  slight  excess ;  or  from  baryta  by 
sulphuric  acid,  and  from  strontia  and  lime  by  sulphuric  acid 
and  alcohol ;  and  from  the  fixed  alkalies  by  precipitation  with 
oxalate  of  ammonia. 


SECTION   VI. 

LANTHANUM. 

-Ey.  47,  or  588;  La. 

The  red-brown  oxide  obtained  from  cerite  by  the  methods 
already  described  (p.  2G1),  and  originally  regarded  as  the 
oxide  of  a  single  metal,  cerium,  was  shown  by  Mosander  *,  in 
1839,  to  contain  the  oxide  of  another  metal,  to  which  he 
gave  the  name  lanthanum.  Subsequently,  in  1841  f,  Mosan- 
der discovered  that  even  this  supposed  simple  oxide  contained 
two  distinct  metals,  for  one  of  which  the  name  of  lantbanmn 

«  Pogg.  Ann.  xlvi.  G48  j  xlrii.  207.  f  Ibid.  Ivi.  504. 


LANTHANUM.  269 

was  retained^  while  the  other  was  called  didymium.  These 
two  metals  appear  to  be  constantly  associated  with  cerium, 
though  not  always  in  the  same  proportion. 

The  separation  of  lanthanum  and  didymium  from  cerium 
may  be  effected  by  either  of  the  methods  already  described 
(p.  262)  j  the  second  and  third  are  easier  and  more  expe- 
ditious than  the  first.  If  the  solution  obtained  by  treating 
the  crude  red-brown  oxide  with  dilute  nitric  acid  be  evapo- 
rated to  dryness,  and  the  residue  treated  with  nitric  acid 
diluted  with  at  least  200  parts  of  water,  a  solution  will  be 
obtained  quite  free  from  cerium  (Marignac).  Boiling  the 
red-brown  oxide  with  chloride  of  ammonium  also  yields  a  solu- 
tion of  lanthanum  and  didymium  free  from  cerium.  In  both 
cases,  however,  it  is  best  to  test  a  portion  of  the  solution  for 
cerium  by  precipitating  with  excess  of  caustic  potash,  and 
passing  chlorine  through  the  solution.  The  presence  of 
cerium,  even  in  very  small  quantity,  will  be  indicated  by  the 
formation  of  a  yellow  precipitate,  after  the  liquid,  supersatu- 
rated with  chlorine,  has  been  left  in  a  close  vessel  for  several 
hours. 

A  solution  free  from  cerium  having  been  obtained,  the 
separation  of  the  lanthanum  and  didymium  is  effected  by  the 
different  solubilities  of  their  sulphates.  To  convert  them  into 
sulphates,  the  solution  is  treated  with  excess  of  a  caustic  alkali, 
and  the  washed  precipitate  dissolved  in  dilute  sulphuric  acid. 
The  mode  of  proceeding  varies  according  as  the  lanthanum  or 
the  didymium  is  in  excess. 

1.  When  the  lanthanum  is  in  excess,  in  which  case  the 
solution  has  but  a  faint  amethyst  tinge,  the  liquid  is  evapo- 
rated to  dryness,  and  the  residue  heated  in  a  platinum- dish 
to  a  temperature  just  below  redness,  to  drive  off  the  excess  of 
acid,  and  render  the  sulphates  perfectly  anhydrous.  The 
residue  is  then  dissolved  in  rather  less  than  six  times  its 
weight  of  water,  at  about  36°  Fah.  (2°  or  3°  C),  the  salt 
being  reduced  to  powder  and  added  in  successive  small  portions, 

r  2 


270  LANTHANUM. 

and  the  vessel  containing  the  liquid  being  immersed  in  ice-cold 
water.  Without  these  precautions,  the  temperature  of  the 
liquid  may  be  raised  several  degrees,  in  consequence  of  the 
heat  evolved  by  the  combination  of  the  anhydrous  sulphates 
with  water;  and,  in  that  case,  crj'stallisation  will  commence, 
and  rapidly  extend  through  the  whole  mass  of  liquid,  as  these 
sulphates  are  much  less  soluble  in  warm  than  in  cold  water  ; 
but  if  the  liquid  be  properly  cooled,  the  whole  dissolves  com- 
pletely. The  solution  is  next  to  be  heated  in  the  water-bath 
to  about  104°  F.  (40°  C.) ;  the  sulphate  of  lanthanum  theu 
crystallises  out,  accompanied  by  only  a  small  quantity  of 
sulphate  of  didymium.  To  purify  it  completely,  it  is  again 
rendered  anhydrous,  redissolved  in  ice-cold  water,  &c.,  and 
the  entire  process  repeated  ton  or  twelve  times.  The  test  of 
purity  is  perfect  whiteness,  the  smallest  quantity  of  didymium 
imparting  an  amethyst  tinge  (Mosander). 

2.  When  the  didymium-salt  is  in  excess,  in  which  case  the 
liquid  has  a  decided  rose-colour,  separation  may  be  effected 
by  leaving  the  solution  containing  excess  of  acid,  in  a  warm 
place  for  a  day  or  two.  The  sulphate  of  didymium  then  sepa- 
rates in  large  rhombohedral  crj^stals  modified  with  numerous 
secondary  faces;  and,  at  the  same  time,  slender,  needle- 
shaped,  violet-coloured  crystals  are  formed,  containing  the 
two  sulphates  mixed.  The  rhomboliedral  crystals,  which  are 
nearly  free  from  lanthanum,  are  removed,  and  the  needles, 
together  with  the  mother-liquid,  treated  as  in  the  first 
method,  to  obtain  sulphate  of  lanthanum  (Mosander). 

In  both  cases,  the  separation  may  be  greatly  facilitated  by 
first  dissolving  the  mixed  oxides  of  the  two  metals  in  a  large 
excess  of  nitric  acid,  and  precipitating  in  successive  portions 
by  oxalic  acid  :  the  first  precipitates  thus  formed  have  a  much 
deeper  rose-colour,  and  are  much  richer  in  didymium  than 
the  latter.  The  separation  thus  effected  is  very  imperfect  in 
itself,  but  it  greatly  facilitates  the  subsequent  separation  of 
the  sulphates,  which  is  much  more  rapid,  when  one  of  the 


LANTHANUM.  ^71; 

sulphates  is  in  great  excess  with  regard  to  the  other  (Ma- 
rignac) . 

Metallic  lanthanum  is  obtained  by  decomposing  the  anhy- 
drous chloride  with  sodium,  and  dissolving  out  the  chloride 
of  sodium  with  alcohol  of  sp.  gr.  0-833.  It  is  a  dark,  lead- 
grey  powder,  soft  to  the  touch,  and  adhering  when  pressed. 

Protoxide  of  lanthanum,  LaO,  55  or  688,  is  obtained  in 
the  anhydrous  state  by  igniting  the  precipitated  hydrate  or 
carbonate  in  a  covered  crucible.  It  is  a  white  powder,  which 
turns  brown  when  heated  in  the  air,  probably  from  partial 
conversion  into  a  higher  oxide.  The  hydrated  oxide  is  formed 
when  the  metal  or  the  anhydrous  oxide  is  immersed  in  warm 
water,  or  when  a  salt  of  lanthanum  is  precipitated  by  caustic 
potash.  It  is  a  white  substance,  viscid  while  moist,  and 
slightly  alkaline  to  test-paper.  It  absorbs  carbonic  acid  from 
the  air  with  great  rapidity. 

Oxide  of  lanthanum,  even  after  strong  ignition,  dissolves 
very  easily  in  acids.  When  boiled  with  a  solution  of  chloride 
of  ammonium,  it  dissolves  and  expels  the  ammonia.  The 
salts  of  lanthanum  are  perfectly  colourless  when  free  from 
didymium.  The  soluble  salts  have  an  astringent  taste. 
Potash  and  soda,  added  to  the  solutions,  throw  down  the 
hydrated  oxide,  which  dissolves  completely  in  chlorine-water, 
Avithout  forming  any  yellow  deposit.  Ammonia  throws  down 
a  basic  salt.  Oxalic  acid  or  oxalate  of  ammonia,  throws 
down  a  white  flocculent  precipitate,  which  does  not  become 
crystalline.  In  other  respects,  the  solutions  resemble  those 
of  cerous  salts.  Compounds  of  lanthanum  do  not  impart  any 
colour  to  borax  or  phosphorus-salt. 

Chloride  of  lanthanum  is  obtained  in  the  anhydrous  state 
by  igniting  the  oxide  in  a  current  of  hydrochloric  acid  gas, 
and  as  a  hydrate  by  evaporating  a  solution  of  the  oxide  in 
hydrochloric  acid.     It  dissolves  very  readily  in  water. 

Carbonate  of  lanthanum  is  found  native  in  small  crystalline 
scales,  containing  traces  of  protoxide  of  cerium.     When  ob- 

u  3 


272  ESTIMATION    OF    LANTHANUM. 

tained  by  precipitation,  it  forms  a  gelatinous  mass,  which 
gradually  changes  into  shining  crystalline  scales    (Mosander). 

Sulphate  of  lanthanum,  LaO .  SO3,  is  obtained  by  spon- 
taneous evaporation  in  small  prismatic  crystals,  containing 
3  eq.  of  water  of  crystallisatipn.  It  parts  with  its  water  at  a 
low  red  heat,  and  with  half  its  acid  at  a  strong  red  heat.  It 
is  much  less  soluble  in  hot  than  in  cold  water  (p.  272).  It 
forms  with  sidphate  of  potash  a  very  sparingly  soluble  double 
salt,  similar  to  the  sulphate  of  cerium  and  potassium. 

Nitrate  of  lanthanum  crystallises  in  deliquescent  colourless 
prisms,  very  easily  soluble  in  water  and  in  alcohol.  When 
carefully  heated,  so  as  not  to  expel  any  of  the  acid,  it  fuses, 
and  solidifies  into  a  colourless  glass  on  cooling.  If  the  heat 
is  raised,  so  as  to  drive  off  a  portion  of  the  acid,  a  fused  mass 
remains  which,  on  cooling,  forms  a  kind  of  enamel,  but 
almost  immediately  afterwards  crumbles  to  a  bulky  white 
powder,  and  with  such  force  that  the  particles  are  scattered 
about  to  a  considerable  distance  (Mosander). 


ESTIMATION    OF    LANTHANUM. 

Lanthanum  is  precipitated  from  its  solutions  by  potash,  or 
by  oxalate  of  ammonia,  and  the  precipitate  converted  by 
ignition  in  a  covered  platinum  crucible  into  the  anhydroils 
oxide,  containing  85*7  per  cent,  of  the  metal. 

The  methods  of  separating  lanthanum  from  other  metals 
are  the  same  as  those  adopted  for  cerium.  The  separation  of 
lanthanum  from  cerium  itself  may  be  effected  by  boiling  the 
mixed  oxides  in  a  solution  of  chloride  of  ammonium  (p.  262) . 


DIDYMIUM.  273 


SECTION   VII. 

DIDYMIUM. 

Eq.  48  or  600;  Di. 

Didymium  was  discovered  by  Mosander  in  1841*;  and 
its  compounds  liave  since  been  more  minutely  examined  by 
Marignac.f 

A  pure  salt  of  didymium  is  obtained  by  recrystallising  the 
rose-coloured  rbombobedrons  wbich  separate  from  an  acid 
solution  of  the  mixed  sulphates  of  lanthanum  and  didymium 
by  spontaneous  evaporation ;  and  from  the  pure  sulphate  thus 
prepared,  the  other  compounds  of  the  metal  may  be  formed. 

Metallic  didymium  is  obtained  by  heating  potassium  with 
an  excess  of  chloride  of  didymium,  and  washing  out  the 
soluble  chlorides  with  cold  water.  It  is  thus  obtained,  for 
the  most  part,  as  a  grey  metallic  powder ;  but  partly,  also,  in 
fused  globules.  The  powder,  thrown  into  the  flame  of  a 
spirit-lamp,  burns  with  bright  sparks  like  iron-filings.  The 
powder  decomposes  water  at  ordinary  temperatures  ;  the 
fused  granules  do  not :  in  either  form,  however,  the  metal 
dissolves  rapidly  in  dilute  acids,  with  evolution  of  hydrogen. 

Protoxide  of  didymium,  DiO,  56  or  700.  —  Obtained  in 
the  anhydrous  state  by  strongly  igniting  the  nitrate,  oxalate, 
or  the  precipitated  hydrate  in  a  covered  crucible.  It  is  per- 
fectly white ;  is  slowly  converted  into  a  hydrate  by  immersion 
in  warm  water ;  dissolves  readily  in  the  weakest  acids ;  and 
expels  ammonia  from  ammoniacal  salts  when  boiled  with 
them.  The  hydrate,  DiO. HO,  is  a  gelatinous  mass  resembling 
alumina,  but  having  a  very  pale  rose-colour.  It  contracts 
much  by  desiccation. 

*  Pogg.  Ann.  Ivi.  504. 

t  Ann.  Ch.  Phjs.  [3],  xxxviii.  148  j  Chem.  Soc.  Qu,  J.,  vi.  260. 

U  4 


274  DIDYMIUM. 

The  salts  of  didymium  have  either  a  pure  rose-colour,  like 
the  sulphate,  or  slightly  inclining  to  violet,  like  the  nitrate  in 
the  state  of  strong  solution.  Potash,  soda,  and  ammonia 
precipitate  the  hydrate ;  so  does  sulphide  of  ammonium. 
Carbonate  of  baryta  also  throws  down  the  hydrated  oxide 
slowly,  but  completely.  Oxalate  of  ammonia  precipitates 
didymium  completely  from  neutral  solutions;  and  oxalic  acid 
almost  completely,  unless  the  solution  contains  a  large  excess 
of  acid.  The  sulphates  of  potash,  soda,  and  ammonia  form, 
immediately  in  strong,  and  gradually  in  weak  solutions,  rose- 
white  precipitates  of  double  sulphates,  shghtly  soluble  in 
water,  less  soluble  in  excess  of  the  reagent ;  the  soda-salt  is 
the  least  soluble  of  the  three.  Phosphoric  and  arsenic  acids, 
at  a  boiling  heat,  form  precipitates  sparingly  soluble  in  acids. 
All  compounds  of  didymium  impart  to  borax  and  phosphorus- 
salt  a  very  pale  rose-colour.  They  do  not  colour  carbonate 
of  soda  before  the  blowpipe. 

Peroxide  of  didymium. — When  the  oxalate,  nitrate,  car- 
bonate, or  hydrate  of  didymium  is  ignited  in  contact  with  the 
air,  and  not  very  strongly,  a  dark  brown  oxide  is  obtained, 
containing  from  0-32  to  0*88  per  cent,  of  oxygen  more  than 
the  protoxide.  'V\Tien  treated  with  acids  it  dissolves  readily, 
giving  off  the  excess  of  oxygen,  and  forming  a  solution 
containing  the  protoxide.  It  is  probably  a  mixture  of  the 
protoxide  with  a  small  quantity  of  a  higher  oxide  of  definite 
composition.  By  strong  ignition  in  a  close  vessel,  it  is  con- 
verted into  the  white  protoxide. 

Sulphide  of  didymium,  DiS,  is  obtained  by  igniting  the 
oxide  in  the  vapour  of  bisulphide  of  carbon.  It  is  a  light, 
brownish  g^-een  powder,  which  dissolves  in  acids,  with  evo- 
lution of  hydrosulphuric  acid.  A  greyish-white  oxysulphide, 
2DiO.DlS,  is  obtained  by  igniting  the  oxide  with  carbonate 
of  soda  and  excess  of  sulphur,  and  digesting  the  fused  mass  in 
water  (Marignac). 

Chloride  of  didymium  is  obtained  as  a  hydrate  in  rose- 


DIDYMIUM.  275 

coloured  crystals  of  considerable  size,  by  evaporating  a  solution 
of  the  oxide  in  hydrochloric  acid.  The  crystals,  which  are 
very  soluble  in  water  and  alcohol,  contain  DiC1.4H0.  The 
solution,  when  evaporated,  gives  off  hydrochloric  acid,  and 
leaves  an  oxychloride,  not  however  of  constant  composition 
(Marignac). 

Carbonate  of  didymium,  DiO  .  COg.  —  Precipitated  as  a 
white,  bulky  hydrate,  tinged  with  rose-colour,  on  adding  an 
alkaline  carbonate  or  bicarbonate  to  a  salt  of  didymium. 
The  precipitate  formed  in  the  cold  with  nitrate  of  didymium 
and  bicarbonate  of  ammonia,  contains,  after  drying  in  vacuo j 
DiO.Cl2  +  2HO.  At  212°,  it  gives  off  l^-  eq.  water  and  a 
small  quantity  of  carbonic  acid  (Marignac). 

Oxalate  of  didymium,,  C4Di208,  is  precipitated  from  neutral 
solutions  as  a  rose-white  powder,  which  dissolves  in  warm 
nitric  or  hydrochloric  acid,  and  separates,  on  cooling,  in  the 
form  of  a  granular  crystalline  powder,  sometimes  even  in  small 
rose-coloured  prismatic  crystals.  After  drying  in  the  air,  it 
contains  8  eq.  water,  6  eq.  of  which  go  off  at  212°  (Ma- 
rignac) . 

Sulphate  of  didymium,  DiO.S03. —  Formed  by  dissolving 
the  oxide  or  carbonate  in  dilute  sulphuric  acid.  The  solution 
is  rose-coloured,  and  deposits,  by  spontaneous  evaporation, 
dark  rose-coloured,  shining  crystals,  having  the  form  of  an 
oblique  rhomboidal  prism  (Mosander),  and  cleaving  readily 
and  distinctly  in  a  direction  parallel  to  the  base.  They  con- 
tain 3(DiO.S03)  +  8  Aq.,  and  give  off  the  whole  of  their 
water  at  392°  F.  (200°  C),  leaving  an  anhydrous  powder, 
which  may  be  heated  to  redness  without  further  alteration. 
A  solution  of  the  sulphate,  when  heated,  especially  to  the 
boiling  point,  deposits  a  crystalline  precipitate  containing 
DiO.SOg  +  2H0.  The  following  table  exhibits  the  solu- 
bility of  the  anhydrous  salt,  and  of  the  two  crystalline  hydrates 
in  water  at  different  temperatures : — 


276 


DIDYMIUM. 

perature. 

Anhydrous 
Sulphate. 

\          Sulphate  with 
2  eq.  water. 

Sulphate  crystallised 
iu  the  cold. 

12°  C 

431 

— 

— 

14 

39-3 

— 

— 

18 

25-8 

16-4 

— 

19 

— 

— 

11-7 

25 

20-6 

— 

— 

38 

130 

— 

4D 

— 

— 

8-8 

50 

110 

— 

6-5 

00 

— 

— 

1-7 

The  anhydrous  sulphate,  exposed  to  the  heat  of  an  intense 
charcoal  fire,  gives  off  two-thirds  of  its  sulphuric  acid,  and 
leaves  a  tribasic  sulphatCy  3DiO.S03  (Mariguac). 

Sulphate  of  didymium,  mixed  in  solution  with  sulphate  of 
potash,  forms  a  crystalline  double  salt,  which  appears  to  con- 
tain KO.SO3  +  3(DiO.S03)  +  2H0;  it  dissolves  in  sixty- 
three  times  its  weight  of  cold  water.  With  sulphate  of  soda 
it  forms  the  anhydrous  double  salt,  NaO.SOg  +  3(DiO.S03), 
which  requires  two  hundred  times  its  weight  of  water  to  dis- 
solve it,  and  is  still  less  soluble  in  a  solution  of  sulphate  of 
soda.  With  sulphate  of  ammonia,  it  forms  the  salt  NH^O.SOg 
-I-  3(DiO.S03)  +  8H0,  soluble  in  eighteen  times  its  weight 
of  water  (Marignac). 

Sulphite  of  didymium,  DiO.SOs  +  2H0.  — Oxide  of  didy- 
mium suspended  in  water,  is  readily  dissolved  by  a  stream  of 
sulphurous  acid  gas,  forming  a  rose-coloured  solution  which 
becomes  tui'bid  when  heated,  forming  a  light  bulky  precipitate, 
which  redissolves  as  the  liquid  cools,  unless  the  temperature 
has  been  raised  to  the  boiling  point,  in  which  case  it  remains 
undissolved  (Marignac) . 

Nitrate  of  didymium,  DiO.NOg. — This  salt  is  very  soluble 
in  water  and  in  alcohol  of  the  strength  of  96  per  cent.  The 
aqueous  solution  has  a  pure  rose  colour  when  dilute,  but 
appears  violet  by  reflected  light  when  strong.     A  syrupy  solu- 


TANTALUM.  27  f 

tion  solidifies  on  cooling  into  a  deliquescent  crystalline  mass, 
which,  when  carefully  heated  to  300°  C,  melts,  becomes  per- 
fectly anhydrous,  and  exhibits  the  composition  of  the  neutral 
nitrate.  At  a  higher  temperature,  it  is  decomposed,  giving 
off  nitrous  fumes,  and  leaving  a  residue  from  which  water 
extracts  a  portion  of  neutral  nitrate,  and  leaves  a  basic  salt 
containing  4DiO.N05  +  5 HO.   (Marignac) . 

Phosphate  of  didymium,  SDiO.POg  +  2H0.  —  Precipi- 
tated, after  a  few  hours,  as  a  white  powder,  on  adding  a  strong 
solution  of  phosphoric  acid  to  a  strong  solution  of  nitrate  of 
didymium.  It  is  insoluble  in  water,  very  sparingly  soluble  in 
dilute  acids ;  but  dissolves  readily  in  the  stronger  acids  when 
coDcentrated;  gives  off  its  water  when  ignited  (Marignac). 

Arse7iiate  of  didymium,  5Di0.2As05  +  2H0.  —  Obtained 
as  a  pulverulent  precipitate  by  the  action  of  arsenic  acid  on 
solutions  of  didymium  at  the  boiling  heat,  or  as  a  gelatinous 
precipitate  by  the  action  of  neutral  arseniate  of  potash  at 
ordinary  temperatures.  It  is  but  slightly  soluble  in  dilute 
acids  (Marignac). 

The  quantitative  estimation  of  didymium  is  effected  in  the 
same  manner  as  that  of  lanthanum.  The  anhydrous  prot- 
oxide contains  85*7  per  cent,  of  the  metal. 

The  methods  of  separating  didymium  from  the  preceding 
metals  are  also  the  same  as  for  lanthanum.  For  separating 
it  from  lanthanum  itself,  no  method  has  yet  been  devised 
sufficiently  exact  for  quantitative  analysis. 


SECTION    VIII. 

TANTALUM. 

Eq.  68-82  or  860'3  ;  Ta. 

This  metal  was  discovered  by  Ekeberg  in  1802.  It  is  a 
rare  metal,  occurring  only  in  a  few  minerals,  the  principal  of 
which  are  Swedish  tantalite  and  yttro-tantalite. 


278  TANTALUM. 

Tantalum  is  obtained,  in  the  metallic  state,  by  heating  the 
fluoride  of  tantalum  and  potassium,  or  fluoride  of  tantalum 
and  sodium,  with  sodium,  in  a  well  covered  iron  crucible,  and 
afterwards  washing  out  the  soluble  salts  by  water.  The  re- 
duced metal  thus  obtained  is  not  quite  piu'e,  being  more  or  less 
contaminated  with  acid  tantalate  of  soda,  the  quantity  of 
which  may,  however,  be  diminished  by  covering  the  mixture 
in  the  crucible  witli  chloride  of  potassium. 

Tantalum  is  a  black  powder,  which,  according  to  II.  Rose, 
is  a  good  conductor  of  electricity.  When  heated  in  the  air, 
it  bums  with  a  bright  light,  and  is  converted,  tliough  with 
difficulty,  into  tantalic  acid.  It  is  not  attacked  by  sulphuric, 
liydi'ochloric,  or  nitric  acid,  or  even  by  aqua  regia.  It  dis- 
solves slowly  in  warm  aqueous  hydrofluoric  acid,  with  evolu- 
tion of  hydrogen,  and  very  rapidly  in  a  mixture  of  hydrofluoric 
and  nitric  acids. 

Tantalum  forms  two  compounds  with  oxygen,  viz.,  tantalous 
acid,  probably  TaO,  and  tantalic  acid,  TaOj. 

Tantalous  acid  is  ol)tained  by  placing  tantalic  acid  in  a 
small  cavity  in  a  crucible  filled  with  charcoal,  and  exposing  it 
to  the  strongest  heat  of  a  blast-furnace ;  a  thin  film  on  the 
outside  is  at  the  same  time  reduced  to  the  state  of  metal.  It 
is  a  dark  grey  mass  which  scratches  glass,  and  acquires 
metallic  lustre  by  bm'nishing. 

Tantalic  acid,  TslO^;  84-82  or  1060-3.*  —  This  compound 
is  formed  when  tartalum  bums  in  the  air;  also  by  the  action 
of  water  on  chloride  of  tantalum;  and,  in  the  form  of  a 
potash-salt,  by  fusing  metallic   tantalum  or  tantalous  acid 

*  The  composition  of  tantalic  acid  is  usually  represented  by  the  formula 
TaOg,  which,  according  to  the  original  analysis  of  that  compound  by  Ber- 
relius  (88'5  per  cent,  tantalum  +  11-5  per  cent,  oxygen),  gives  for  tantalum 
the  equivalent  number  185.  But  according  to  the  recent  experiments  of 
H.  Rose  (Berl.  Akad.  Ber.  1856,  385),  the  tantalum-compounds  appear  to  con- 
tain 2  eq.  of  the  chlorous  element,  viz.,  the  chloride,  TaCla,  tantalic  acid, 
TaOo,  &c. ;  he  also  finds  the  cliloride  to  contain  49-25  per  cent,  of  tantalum, 
making  the  equivalent  of  tantalum  6882. 


TANTALIC    ACID. 


279 


-with  hydrate,  carbonate,  or  bisulphate  of  potash.     It  exists, 
in  combination  with  various  bases,   in   the  minerals  above 
mentioned,  and  is  usually  extracted  from  tantalite,  which  con- 
tains the  oxides  of  iron  and  manganese,  together  with  small 
quantities  of  stannic  and  tungstic  acids,  by  one  of  the  follow- 
ing processes:  —  1.  The  mineral,  after  being  pulverised  and 
levigated,  is  fused  with  twice  its  weight  of  hydrate  of  potash ; 
the  fused  mass  digested  in  hot  water;  and  the  filtered  solution 
supersaturated  with  hydrochloric  or   nitric  acid :    hydrated 
tantalic  acid  is  then  precipitated  in  white  flakes,  which  may  be 
purified  by  washing  with  water  (Berzelius).      2.    A  better 
method,   however,   is   to   fuse   the   levigated   tantalite   in  a 
platinum    crucible   with   six   or   eight   times   its   weight   of 
bisulphate  of  potash ;  pulverise  the  mass  when  cold ;  and  boil 
it  repeatedly  with  fresh  quantities  of  water  till  no  more  sul- 
phate of  potash,  iron,  or  manganese  is  dissolved  out  of  it. 
The  residue,  which  consists  of  hydrated  tantalic  acid  mixed 
with  ferric  oxide,   stannic   acid,  and  tungstic  acid,  is  then 
digested   in   sulphide   of   ammonium    containing    excess   of 
sulphur,  which  removes  the  stannic  and  tungstic  acids,  and 
converts  the  iron  into  sulphide ;  the  liquid  is  filtered,  and  the 
tantalic  acid  washed  with  water  containing  sulphide  of  am- 
monia, then  boiled  with  strong  hydrochloric  acid  to  remove 
the  iron,  and  finally  washed  with  boiling  water.    The  hydrated 
tantalic  acid  thus  prepared  is  converted  into  the  anhydrous 
acid  by  ignition.     It  may  still,  however,  contain  silica,  to  re- 
move which,  it  is  dissolved  in  aqueous  hydrofluoric  acid,  the 
filtered  solution  mixed  with  sulphuric  acid  and  evaporated  to 
dryness,  and  the  residue  ignited  as  long  as  its  weight  con- 
tinues to  diminish :    the  silica  is  then  expelled  as  gaseous 
fluoride  of  silicon  (Berzelius) . 

Anhydrous  tantalic  acid  is  a  white  powder,  which  remains 
white  when  heated,  or  acquires  but  a  very  faint  tinge  of 
yellow.  Its  specific  gravity  varies  from  7'022  to  8-264,  in- 
creasing with  the  temperature  to  which  the  acid  has  been 


280  TANTALUM. 

exposed  (H.  Rose).  It  neither  melts  nor  volatilises  wlien 
heated,  and  is  destitute  of  taste  and  smell.  It  is  reduced  to 
the  metallic  state  in  the  circuit  of  a  very  powerful  voltaic 
battery ;  partially  also  by  very  strong  ignition  in  contact  with 
charcoal.  When  ignited  in  the  vapour  of  bisulphide  of  carbon, 
it  yields  sulphide  of  tantalum  : 

2Ta02  +  4CS2  =  Ta2S3  +  4C0  +  58. 

It  is  insoluble  in  all  acids,  and  can  only  be  rendered  soluble 
by  fusion  with  hydrate  or  carbonate  of  potash. 

Hydrated  tantalic  acid,  obtained  by  precipitating  an  aqueous 
solution  of  tantalate  of  potash  with  hydrochloric  acid,  or  by 
decomposing  chloride  of  tantalum  with  water  containing  a 
small  quantity  of  ammonia,  is  a  snow-white  bulky  powder, 
which  reddens  litmus-paper  while  moist,  and  dissolves  in 
hydrochloric  and  hydrofluoric  acids.  AVhen  strongly  heated 
it  gives  off  its  water  and  becomes  incandescent.  The  hydrate, 
obtained  by  fusing  tantalite  with  bisulphate  of  potash  in  the 
manner  above  described,  is  of  a  denser  and  more  ciystalline 
character,  is  insoluble  in  all  acids  excepting  strong  sulphuric 
acid,  and  is  precipitated  from  the  solution  by  water.  When 
heated,  it  becomes  anhydrous,  but  does  not  emit  light. 

Tantalic  acid  combines  with  banes  much  more  readily  than 
with  acids.  When  fused  with  hydrate  of  potash  in  a  silver 
ciiicible,  it  forms  a  transparent  mass  of  tantalate  of  potash, 
which,  after  cooling,  dissolves  completely  in  water.  With 
hydi^ate  of  soda  it  fuses  into  an  opaque  turl)id  mass,  and 
ultimately  deposits  a  sediment,  which  is  not  taken  up  by 
fusion  with  any  excess  of  the  alkali.  Water  poured  upon  the 
fused  mass  when  cokl  dissolves  out  the  excess  of  soda,  but  not 
a  trace  of  tantalic  acid ;  and  the  residue,  when  treated  with 
fresh  water,  dissolves  and  forms  an  opalescent  solution  of 
acid  tantalate  of  soda,  which  salt  is  completely  insoluble  in  a 
strong  solution  of  caustic  soda,  and  is  therefore  precipitated 
on  mixing  the  liquid  with  the  solution  of  soda  previously 


TANTALIC    ACID.  281 

obtained  by  treating  the  fused  mass  with  water.  When  tan- 
talic  acid  is  fused  with  carbonate  of  potash  or  soda^  the  fused 
mass  is  not  completely  soluble  in  water. 

Hydrochloric  acid,  added  in  excess  to  the  solution  of 
an  alkaline  tantalate,  first  precipitates  the  tantalic  acid, 
and  then  redissolves  it,  forming  a  slightly  opalescent  liquid, 
Sulphuric  acid  also  precipitates  the  tantalic  acid,  but  does 
not  redissolve  it  when  added  in  excess.  Carbonic  acid 
gas,  passed  through  the  solution  of  an  alkaline  tantalate, 
precipitates  the  whole  of  the  tantalic  acid  in  the  form  of 
an  acid  salt.  Chloride  or  sulphate  of  ammonium  also  pre- 
cipitates the  tantalic  acid  from  these  solutions  in  the  form 
of  hydrate,  mixed  with  small  quantities  of  ammonia  and  the 
fixed  alkali.  The  presence  of  carbonate  of  potash  or  soda 
prevents  the  formation  of  this  precipitate  at  ordinary  tem- 
peratures ;  but  it  then  appears  after  boiling  for  some  time. 
Sulphide  of  ammonium  produces  no  precipitate.  Chloride  of 
barium  or  calcium  forms  a  precipitate  of  tantalate  of  baryta 
or  lime,  insoluble  in  water  and  in  ammoniacal  salts.  Nitrate 
of  silver  forms,  in  the  solution  of  a  neutral  alkaline  tantalate, 
a  white  precipitate,  which  is  turned  brown  by  a  small  quantity 
of  ammonia,  and  dissolves  in  a  larger  quantity.  A  solution 
of  basic  mercurous  nitrate  forms  a  yellowish  white  precipitate, 
which  turns  black  when  heated.  Ferrocyanide  of  potassium, 
added  to  a  very  slightly  acidulated  solution  of  an  alkaline 
tantalate,  forms  a  yellow  precipitate ;  ferricyanide  of  potassium 
a  white  precipitate.  Infusion  of  galls,  added  to  a  solution  of 
an  alkaline  tantalate  acidulated  with  sulphuric  or  hydrochloric 
acid,  forms  a  light  yellow  precipitate  soluble  in  alkalies. 
Zinc,  immersed  in  the  solution  of  an  alkaline  tantalate  acidu- 
lated with  hydrochloric  acid,  does  not  produce  any  blue 
colour ;  neither  is  that  colour  produced,  or  but  very  faintly, 
on  addition  of  sulphuric  acid.  But  if  chloride  of  tantalum 
be  dissolved  in  strong  sulphm-ic  acid,  and  then  water  and 
metallic  zinc  added,  a  fine  blue  colour  is  produced,  which  does 


282  TANTALUM. 

not  change  to  brown,  but  soon  disappears.  The  blue  eolour 
is  also  produced  on  placing  zinc  in  a  solution  of  chloride  of 
tantalum  in  hydrochloric  acid,  to  which  a  small  quantity  of 
water  has  been  added ;  too  much  water,  however,  prevents  its 
formation. 

Before  the  blowpipe,  tantalic  acid  dissolves  abundantly  in 
phosphorus-salt,  forming  a  clear,  colourless  glass,  which  un- 
dergoes no  alteration  when  heated  in  the  inner  flame,  and 
does  not  turn  red  on  addition  of  protosulphate  of  iron.  AVith 
borax  also  it  forms  a  transparent  glass,  which,  however,  if  the 
quantity  of  tantalic  acid  is  somewhat  large,  may  be  rendered 
opaque  by  interrupted  blowing,  or  flaming,  as  it  is  technically 
called,  but  recovers  its  transparency  by  long  exposure  to  a 
continued  blast.  A  very  large  quantity  of  tantalic  acid  ren- 
ders the  glass  opaque.  No  alteration  takes  place  in  the  inner 
flame.  With  carbonate  of  soda  on  charcoal,  tantalic  acid 
produces  efibrvescence,  but  does  not  fuse  into  a  bead  or  undergo 
reduction. 

The  above-described  characters  are  sufficient  to  distinguish 
tantalic  acid  from  all  the  substances  previously  described. 
From  titanic  acid,  which  it  most  resembles,  it  is  distinguished, 
first,  by  its  behaviour  before  the  blowpipe ;  secondly,  l)y  its  per- 
fect insolubility  in  strong  suli)huric  acid  after  ignition,  ignited 
titanic  acid,  when  finely  pulverised,  being  soluble  in  that 
acid ;  and,  thirdly,  by  the  fact  that,  when  it  is  fused  with  bi- 
sulphate  of  potash,  and  the  fused  mass  treated  with  cold 
water,  the  tantalic  acid  remains  undissolved  in  combination 
with  sulphuric  acid;  whereas  titanic  acid,  similarly  treated, 
yields  a  fused  mass,  which  dissolves  completely  in  a  con- 
siderable quantity  of  cold  water,  provided  the  fusion  has  been 
continued  long  enough.  From  silica,  tantalic  acid  is  distin- 
guished by  its  behaviour  before  the  blowpipe,  silica  being  in- 
soluble in  phosphorus-salt,  and  fusing  to  a  transparent  bead 
when  heated  on  charcoal  with  a  small  quantity  of  carbonate 
of  soda.     The  behaviour  of  tantalic  acid  with  zinc,  with  tine- 


CHLORIDE    OF    TANTALUM.  28S 

ture  of  galls^  and  with  hydrofluoric  acid,  also  distinguishes  it 
from  silica. 

Sulphide  of  tantalum,  TagSg.  —  Obtained  by  igniting  tan- 
talic  acid  in  the  vapour  of  bisulphide  of  carbon,  or  by  ex- 
posing chloride  of  tantalum  to  the  action  of  hydrosulphuria 
acid  gas.  The  product  is  not  perfectly  definite  in  either  case. 
The  second  process  yields  a  sulphide  containing  24*08  per 
cent,  sulphur,  whereas  the  formula  Ta2S3  requires  25 -86  per 
cent.  The  former  process  gives  a  product  containing  28*5 
per  cent,  sulphur.  Sulphide  of  tantalum  is  a  black  substance, 
which  acquires  a  brass-yellow  colour  by  trituration  in  an 
agate  mortar.  Heated  in  an  atmosphere  of  chlorine  gas,  it  is 
converted  into  chloride  of  tantalum  and  chloride  of  sulphur 
(H.  Rose). 

Chloride  of  tantalum,  TaClg. — Prepared  by  passing  chlorine 
gas  over  a  heated  mixture  of  tantalic  acid  and  charcoal. 
Tantalic  acid  is  mixed  with  starch  or  sugar,  and  the  mixture 
completely  charred  by  ignition  in  a  covered  crucible.  It  is 
then  introduced  in  small  pieces  into  a  glass  tube  which  is 
strongly  heated  by  a  charcoal  fire,  while  a  stream  of  dry 
carbonic  acid  is  passed  through  it.  As  soon  as  all  the 
moisture  is  expelled,  the  tube  is  left  to  cool,  the  flow  of  car- 
bonic acid  being  still  kept  up ;  the  carbonic  acid  apparatus  is 
then  replaced  by  a  chlorine  apparatus,  and  the  tube  again 
heated  after  the  carbonic  acid  and  atmospheric  air  have  been 
completely  expelled  by  the  chlorine.  Chloride  of  tantalum  is 
then  obtained  in  the  form  of  a  sublimate  of  a  pure  yellow  colour. 
If,  however,  the  tantalic  acid  contains  tungstic  acid,  the 
colour  of  the  sublimate  is  red ;  and  if  stannic  or  titanic  acid 
is  present,  yellow  drops  of  liquid  chloride  are  also  produced. 
Chloride  of  tantalum  melts  at  430°,  and  volatilises  at  291°. 
Water  decomposes  it,  forming  hydrochloric  and  tantalic 
acids;  but  the  decomposition  is  not  complete  even  at  the 
boiling  heat :  water  containing  a  small  quantity  of  ammonia 
decomposes  the  chloride  perfectly  even  at  ordinary  tempera- 

VOL.  11.  X 


USL  TANTALUM. 

tures.  According  to  the  recent  experiments  of  II.  Rose, 
chloride  of  tantalum  contains  81*14  per  cent,  of  tantalum. 

Bromide  of  tantalum  is  prepared  in  the  same  manner  as 
the  chloride ;  when  freed  from  excess  of  bromine,  it  has  a 
yellowish  colour. 

Fluoride  of  tantalum,  TaF^. —  Ignited  tantalic  acid  does 
not  dissolve  in  aqueous  hydrofluoric  acid;  but  the  hydrate 
dissolves,  forming  a  clear  solution,  which,  when  evaporated, 
partly  gives  off  the  tantalum  as  fluoride,  but  also  leaves  a 
white  residue  of  oxyfluoride.  Fluoride  of  tantalum  forms 
with  fluoride  of  potassium  a  crystalline  double  salt,  containing 
KF.2TaF2;  and  with  fluoride  of  sodium  the  salt,  NaF.TaFj 
(H.  Rose). 


ESTIMATION  AND  SEPARATION  OF   TANTALUM. 

Tantalum  is  estimated  in  the  form  of  anhydrous  tantalic 
acid,  containing  81*13  per  cent,  of  the  metal.  It  occurs  in 
nature  associated  with  lime,  magnesia,  yttria,  and  the  oxides 
of  iron  and  manganese,  and  occasionally  with  zirconia,  titanic 
acid,  and  a  few  other  substances.  From  these  it  is  separated 
by  fusion  with  hydrate  of  potash,  or,  better,  with  bisulphate 
of  potash,  in  the  manner  already  described  (p.  279).  Some 
comjjounds  of  tantalic  acid  may  be  decomposed  by  sulphuric 
acid,  the  tantalic  acid  being  separated  in  the  insoluble  state, 
and  all  the  bases  passing  into  the  solution. 

Tantalate  of  zirconia  may  be  decomposed  in  this  manner. 
On  treating  that  compound  with  strong  sulphuric  acid,  and 
digesting  the  cooled  mass  for  some  time  with  a  large  quantity 
of  water,  sulphate  of  zirconia  dissolves,  and  tantalic  acid  re- 
mains hehind  in  combination  with  sulphuric  acid,  from  which 
it  may  be  purified  by  repeated  boiling  with  water. 

From  titanic  acid,  with  which  it  sometimes  occurs  in  nature, 
tantalic  acid  is  separated  by  fusing  the  mineral  with  bisulphate 
of  potash,  and  treating  the  fused  mass  with  a  large  quantity  of 


COLUMBIUM.  285 

water.  Titanic  acid  then  dissolves,  especially  if  the  water  is 
slightly  acidulated  with  hydrochloric  acid,  while  sulphate  of 
tantalic  acid  remains  undissolved.  The  titanic  acid  is  preci- 
pitated from  the  solution  by  boiling :  the  separation  is,  how- 
ever, not  very  complete.  In  some  cases,  the  decomposition 
may  be  effected  by  sulphuric  acid. 

From  the  alkalies,  tantalic  acid  may  be  completely  separated 
by  sulphuric  acid,  provided  the  compound  is  soluble  in  water. 
In  the  contrary  case,  it  must  first  be  fused  with  carbonate  or 
hydrate  of  potash.  If,  however,  the  quantity  of  alkali  is  to  be 
likewise  estimated,  the  compound  must  be  rendered  soluble 
by  fusion  with  sulphate  of  ammonia.* 


SECTION     IX, 

COLUMBIUM. 

Synonyme.     Niobium ;  Cb. 

This  metal  was  discovered  by  Hatchett  in  1801,  in  a  black 
mineral  (columbite),  from  Massachusetts,  in  North  America ; 
it  was  thence  named  Columbium.  Wollaston,  in  1809,  ex- 
amined it  further,  and  pronounced  it  to  be  identical  with  the 
tantalum  discovered  by  Ekeberg,  in  Swedish  tantalite.  This 
idea  of  the  identity  of  the  two  metals  remained  current  till 
1846,  when  H.  Rosef,  by  a  more  careful  investigation  of  the 
matter,  was  led  to  conclude  that  the  American  columbite,  and 
the  tantalite  from  Bodenmais,  in  Bavaria,  contained  two  acids 
bearing  a  very  close  resemblance  to  tantalic  acid,  but  never- 
theless, distinct  from  it  and  from  each  other.  To  the  metals 
supposed  to  exist  in  these  acids  he  assigned  the  names  Niobium 
and  Pelopium.     But  by  a  later  investigation  J,  he  finds  that 

*  IT.  Rose,  Handb.  d.  Anal.  Chem.  1851,  ii.  326—335. 
t  Pogg.  Ann.  Ixiii.  317  ;  Ixix.  115. 
X  Pogg.  Ann.  xc.  456  ;  Ann.  Ch.  Pharm.  Ixxxviii.  245. 
X  2 


286  COLUMBIUM. 

these  two  acids  really  contain  the  same  metal,  associated  with 
different  quantities  of  oxygen ;  he  therefore  discards  the  name 
pelopium,  and  proposes  to  designate  by  niobium  the  metal 
contained  in  American  columbite  and  Bavarian  tantalite.  As, 
however,  this  metal  is  clearly  the  one  discovered  fifty  years 
ago  by  Hatchett,  wc  cannot  do  better  than  retain  for  it  the 
name  originally  proposed  by  its  discoverer,  viz.,  Colu^ibium.* 

Columbium  likewise  occurs,  associated  with  yttrium,  ura- 
nium, iron,  and  small  quantities  of  other  metals,  in  a  Siberian 
mineral  called  urano-tantalite,  y ttro-ilmenite,  or  samarskite ; 
also  in  pyrochlore,  cukolite  or  wohlerite,  euxenite,  and  in  a 
variety  of  pitchblende  from  Satersdiilcn. 

Metallic  columbium  is  obtained  by  passing  dry  ammoniacal 
gas  over  the  chloride.  It  is  a  black  powder,  which  oxidises 
when  heated  in  the  air.  Nitric  acid  and  aqua-regia  have  no 
effect  upon  it ;  but  a  mixture  of  hydrofluoric  and  nitric  acids 
attacks  it  at  ordinary  temperatures.  It  combines  with  oxygen 
in  two  proportions,  forming  cohimbous  and  Columbia  acids, 
formerly  supposed  by  Rose  to  contain  different  metals,  and 
called  respectively  niobic  and  pelopic  acids.  The  composition 
of  these  acids  has  not  yet  been  determined. 

Columboiis  acid,  or  a  mixture  of  that  acid  with  columbic 
acid,  is  separated  from  the  minerals  containing  it  by  processes 
similar  to  those  already  described  for  the  preparation  of  tan- 
talic  acid  (p.  279) ;  and  when  the  acid,  or  mixture  of  acids, 
tlius  obtained,  is  mixed  with  charcoal  and  heated  in  a  stream 
of  chlorine  gas,  w  ith  the  precautions  already  detailed  for  the 
preparation  of  chloride  of  tantalum  (p.  285),  it  is  generally 
converted  into  two  chlorides, — the  one  white,  volatile,  but  not 
fusible;  the  other  yellow,  likewise  volatile,  and  easily  fusible  : 
the  latter  contains  the  larger  proportion  of  chlorine.  It  was 
the  formation  of  these  two  chlorides  which  led  Rose  to  con- 
clude that  certain  varieties  of  tantalite  contained  two  distinct 

*  See  a  paper  "  On  the  Nomenclature  of  the  Metals  contained  in  Colum- 
bite and  Tantalite,"  by  Prof.  Connell,  Phil.  Mag.  [4]. 


CHLORIDES    OP    COLUMBIUM.  287 

inetals,  niobium  and  pelopium ;  he  now  finds,  however,  that 
the  substance  which  he  regarded  as  perfectly  pure  niobic 
acid,  obtained  by  the  action  of  water  on  the  white  chloride, 
may,  by  mixing  it  with  a  large  excess  of  charcoal,  and  gently 
igniting  the  mixture  in  a  stream  of  chlorine  gas,  with  strict 
attention  to  all  the  precautions  above  alluded  to,  be  com- 
pletely converted  into  the  yellow  chloride,  —  the  so-called 
chloride  of  pelopium.  But  if  a  smaller  quantity  of  charcoal 
be  used,  or  if  the  mixture  be  too  strongly  ignited  during  the 
action  of  the  chlorine,  especially  at  the  commencement,  the 
white  and  less  volatile  chloride  (chloride  of  niobium),  is 
obtained,  as  well  as  the  yellow  compound. 

Columbium  appears,  then,  to  be  capable  of  uniting  with 
chlorine  in  two  proportions ;  and  the  chlorides  thus  formed 
yield,  when  treated  with  water,  two  acids  of  corresponding 
constitution,  viz.,  Columbous  and  Columbic  acids,  the  latter, 
which  contains  the  larger  proportion  of  oxygen,  being  formed 
from  the  yellow  chloride. 

Columbous  acid  (Rosens  niobic  acid)  may,  like  tantalic 
acid,  be  obtained  in  the  amorphous  and  the  crystalline  state, 
viz.,  by  the  rapid  or  gradual  action  of  water  on  the  chloride. 
Its  specific  gravity  is  lower  than  that  of  tantalic  acid,  and  is 
subject  to  similar  variations.  Samples  of  the  acid,  prepared 
from  various  sources,  exhibited,  after  ignition  over  a  spirit- 
lamp  to  the  point  of  incandescence,  specific  gravities  ranging 
from  4-66  to  5-26;  by  stronger  ignition,  the  density  was 
diminished.  The  mean  density  of  the  amorphous  acid  was 
found  to  be  greater  than  that  of  the  crystalline  in  the  ratio 
of  1  to  0*875.  The  acid  is  colourless  both  in  the  anhy- 
drous and  hydrated  states,  but  when  heated  assumes  a  yellow 
colour,  much  deeper  than  that  of  heated  tantalic  acid.  The 
hydrated  acid  becomes  incandescent  during  its  transition  to 
the  anhydrous  state. 

Columbous  acid  is  decomposed  by  ignition  in  a  stream  of 
hydrosulphuric  acid,  and  converted  into  sulphide  of  colum- 

X  3 


288  COLUMBIUM. 

bium.     When  i^ited  in  ammoniacal  gas,  it  turns  black,  and 
yields  a  large  quantity  of  water. 

Columbous  acid,  after  ignition,  is  insoluble  in  all  acids. 
The  hydrated  acid  is  but  very  sparingly  soluble  in  hydro- 
cliloric  acid ;  so  that  when  an  alkaline  columbite  is  precipi- 
tated by  excess  of  hydrochloric  acid,  the  filtrate  retains  only 
a  trace  of  columbous  acid  in  solution.  The  hydrated  acid  dis- 
Bolves,  to  a  certain  extent,  in  oxalic  and  in  hydrofluoric 
acid. 

The  alkaline  columbites  are  soluble  in  water,  in  solutions 
of  potash  and  carbonate  of  potash,  but  dissolve  with  great 
difficulty  in  excess  of  soda  and  carbonate  of  soda,  more 
sparingly  even  than  tantalate  of  soda.  Columbous  acid  is 
precipitated  from  its  alkaline  solutions  by  acids,  especially  by 
sulphuric  acid,  even  at  ordinary  temperatures ;  whereas  the 
precipitation  of  tantalic  acid  requires  the  aid  of  heat.  Oxalic 
acid  does  not  affect  alkaline  colurabites;  but  carbonic  acid 
gas  precipitates  an  acid  salt  soluble  in  a  large  quantity  of 
water;  acetic  acid  and  sal-ammoniac  also  form  precipitates. 
A  solution  of  an  alkaline  columbite,  acidulated  with  sul- 
phuric or  hydrochloric  acid,  forms  a  red  precipitate  with 
ferrocyanide  of  potassium,  bright  yellow  with  the  ferri- 
cyanidCy  and  orange-red  with  infusion  of  galls.  A  piece  of 
zinCy  immersed  in  the  acidulated  solution,  forms  a  beautiful 
blue  precipitate,  which  after  a  while  changes  to  brown. 

Before  the  blowpipe,  especially  in  the  inner  flame,  colum- 
bous acid  assumes  a  greenish  yellow  colour  while  hot,  but 
becomes  colourless  on  cooling.  With  borax  it  forms  in 
the  outer  flame  a  colourless  bead,  which,  if  the  acid  is  in 
sufficient  quantity,  becomes  opaque  by  flaming.  In  the 
inner  flame,  the  bead  assumes  a  greyish  blue  colour,  provided 
it  contains  a  suflScient  quantity  of  acid  to  produce  opacity  on 
cooling.  In  phosphorus-salt,  the  acid  dissolves  in  large  quan- 
tity, forming  a  colourless  bead  in  the  outer  flame,  and  in  the 
inner,  a  violet-coloured,  or,  if  the  bead  be  saturated  with  the 


COLITMBIC    ACID.  289 

acid,  a  beautiful  blue  bead,  the  colour  disappearing  in  the 
outer  flame.  The  addition  "of  protosulphate  of  iron  changes 
the  colour  to  blood-red.  These  characters,  together  with  the 
above-mentioned  precipitates,  sufficiently  distinguish  colum- 
bous  from  tantalic  acid. 

Columbic  acid  (Rose's  pelopic  acid)  bears  a  very  strong  re- 
semblance to  tantalic  acid,  and  is  intermediate  in  its  pro- 
perties between  that  acid  and  columbic  acid.  Its  specific 
gravity  ranges  from  5*5  to  6'7,  It  appears  to  be  susceptible 
of  three  modifications;  viz.,  amorphous,  crystalline  before 
ignition,  and  crystalline  after  ignition  at  the  heat  of  a  porce- 
lain-furnace. It  is  insoluble  in  all  acids  after  ignition.  It  is 
precipitated  from  its  alkaline  solutions  by  the  same  reagents 
as  columbous  acid.  The  precipitate  formed  by  hydrochloric 
acid  redissolves  in  excess,  forming  an  opalescent  solution 
from  which  the  acid  is  completely  precipitated  by  sulphuric 
acid  at  a  boiling  heat.  The  acidulated  solutions  yield  a 
brownish-red  precipitate  with,  f err  o  cyanide  of  potassium^  white 
with  ferricyanide,  and  orange-yellow  with  infusion  of  galls. 
Zinc  behaves  with  these  solutions  in  the  same  manner  as  with 
solutions  of  tantalic  acid.  A  fine  blue  colour  is  obtained  by 
treating  the  yellow  chloride  of  columbium  with  hydrochloric 
acid,  diluting  with  water,  and  adding  a  piece  of  zinc. 

With  borate  before  the  blowpipe,  columbic  acid  behaves 
like  tantalic  acid.  In  phosphorus-salt  it  dissolves  in  large 
quantity,  forming  a  colourless  bead  in  the  outer  flame.  In 
the  inner  flame,  the  bead  assumes  a  light-brown  colour,  tinged 
with  violet,  the  colour  disappearing  again  after  a  while  in 
the  outer  flame.  The  addition  of  protosulphate  of  iron 
changes  the  brown  colour  to  crimson. 

It  is  remarkable  that  columbic  acid  cannot  be  formed 
directly  from  columbous  acid,  even  by  the  most  powerful 
oxidising  agents.  It  appears,  however,  to  be  deprived  of  a 
portion  of  its  oxygen  by  certain  reducing  agents. 

X  4, 


290  COLUMBIUM. 

The  methods  of  estimating  cohimbium  and  separating  it 
from  other  metals  are  the  same  as  for  tantalum.  No  method 
is  known  of  separating  columbium  from  tantalum ;  but  these 
metals  have  not  hitherto  been  found  occurring  together. 


Ilmenium.  (?)  —  According  to  the  observations  of  K  Hermaim*,  it  would 
appear  that  Siberian  yttrotantalite  or  yttroilmenite  contains  a  peculiar  metal, 
Hmenium,  which  forms  an  acid,  ilmenic  acid,  very  closely  resembling  colum- 
bous  acid,  but  nevertheless  distinct  from  it ;  the  chief  pohits  of  difference 
being  the  lower  specific  gravity,  viz.,  4'1  to  4'2 ;  the  insolubility  of  the 
hydrate  in  hydrochloric  acid ;  and  the  formation  of  a  compound  witli  sul- 
phuric acid  which  is  decomposed  by  a  large  quantity  of  water,  leaving  a 
residue  of  hydrated  ilmenic  acid.  H.  Rosef,  however,  is  of  opinion  that 
the  supposed  ilmenic  acid  is  merely  columbous  [niobic]  acid,  more  or  less 
impure.  Tlie  question  must,  for  the  present,  be  regarded  as  undecided. 
Kose  likewise  regards  yttroUmenite  as  identical  >^ith  urano-tantalite  or 
samarskite. 

*  J.  pr.  Chem.  ixxviii.  91,  119 ;  xl.  475  ;  Ixv.  54. 
t  Pogg.  Ann.  Ixxi.  157. 


MERCURY.  29i 


ORDEE    VIII. 

METALS  WHOSE  OXIDES  AEE  EEDUCED  TO  THE  METALLIC 
STATE  BY  HEAT  (NOBLE  METALS). 

SECTION    I. 

MERCURY. 

Eq.  100  or  1250;    Hg. 

Mercury_,  or  quicksilver,  as  it  is  named  from  its  fluidity,  has 
been  known  from  all  antiquity.  It  is  found  to  a  small  extent 
in  the  metallic  state,  but  its  principal  ore  is  the  native  sulphide 
cinnabar.  The  most  valuable  European  mines  of  mercury 
arc,  those  of  Almaden  in  Spain,  and  of  Idria  in  Illyria.  At 
Almaden  the  cinnabar  is  found  in  veins,  often  nearly  fifty  feet 
thick,  traversing  micaceous  schists  of  the  older  transition 
period :  in  Illyria  it  is  disseminated  in  beds  of  grit,  bitu- 
minous  schist,  or  compact  limestone  of  more  recent  date. 
The  mode  of  extraction  in  both  these  localities,  consists  in 
simply  roasting  the  ore  in  a  distillatory  apparatus,  whereby 
the  sulphur  is  burned  and  converted  into  sulphurous  acid,  while 
the  mercury  is  set  free  in  the  form  of  vapour,  and  condenses 
in  chambers  or  vessels  provided  for  it. 

The  arrangement  adopted  in  Illyria  is  represented  in  figures 
12,  13,  14.  A  is  a  large  furnace  (figs.  12  and  14),  on  each 
side  of  which  is  a  series  of  condensing  chambers,  CCCCCD. 
The  space  V,  separated  from  the  fire-place  by  the  perforated 
arch  n  n',  is  filled  with  the  ore  in  large  lumps ;  smaller  pieces 
are  introduced  into  the  next  compartment  above  the  arch  pp^; 
and  on  the  uppermost  arch,  r  r\  are  laid  a  number  of  earthen 
capsules,  containing  the  pulverised  ore  and  the  mercurial  resi- 
dues of  preceding  operations.    The  fire  being  lighted,  and  the 


292 


MERCURY. 


Fig.  12. 


Fig.  13. 


Fig.  14. 


heat  gradually  raised,  the  sulphur  is  bui-ncd  by  the  air  which 
enters  through  channels  opening  into  the  spaces  G,  H  ;  and 
the  mixture  of  mercurial  vapour,  sulphurous  acid,  and  smoke 
from  the  fire,  passes  through  the  horizontal  channel  at  the 
top  of  the  furnace,  then  up  and  down  through  the  condensing 
chambers,  C  C  C  C,  and  finally  escapes  into  the  air. 


EXTRACTION    OF    MERCURY. 


293 


The  greater  part  of  the  mercury  condenses  in  the  first  three 
chambers_,  whence  it  runs  into  the  channels  abed,  a'h'c'd' ,  which 
conduct  it  into  a  reservoir.  To  facilitate  the  condensation 
of  the  last  portions  of  mercury  in  the  chambers  DD,  the 
vapours  are  made  to  pass  between  a  series  of  boards  placed 
from  side  to  side  of  these  chambers  in  an  inclined  position, 
and  having  a  stream  of  water  continually  running  over  them. 
As  the  mercury  ivhich  condenses  in  these  last  chambers  is 
mixed  with  a  considerable  quantity  of  dust,  it  is  collected  in 
separate  channels,  then  filtered,  and  the  residues  returned  to 
the  furnace  as  already  described. 

The  mercury  obtained  by  this  process  is  purified  by  fil- 
tration through  coarse  linen  cloth,  and  sent  into  the  market 
in  wrought-iron  bottles,  each  containing  about  fifty  pounds. 

At  Almaden,  the  mercury  is  also  extracted  from  the  cin- 
nabar by  roasting,  the  operation  being  conducted  in  furnaces 
called  buytrones.    (Figs.  15  and  16.) 


Fig.  15. 


Fig.  16. 


294 


MEKCURY. 


The  fire  is  made  at  A,  and  the  space  B,  above  it,  is  filled 
with  the  ore,  the  largest  pieces  being  laid  on  tlie  perforated 
arch  at  the  bottom,  smaller  pieces  above,  and  the  whole 
covered  with  lumps  of  a  mixture  of  clay,  powdered  ore,  and 
the  residues  of  preceding  operations.  The  vapours  pass 
through  an  aperture  p,  in  the  upper  part  of  the  furnace,  into 
a  series  of  tubular  vessels  called  alndels,  open  at  both  ends 
and  fitting  one  into  the  other.  These  are  laid  on  a  surface 
Cy  bj  a,  called  the  aludel-bath,  first  descending  a  little,  then 
ascending,  and  finally  opening  into  the  chimney.     The  form 

and  disposition  of  the  aludels  is 
shown  in  figure  17.  The  con- 
densed mercury  escapes  at  the 
joints  of  the  aludels,  and  runs 
into  the  channel  b  b,  by  which  it  is  conveyed  into  the  reser- 
voirs m,  n  n.  The  uncondensed  mercurial  vapour  passes  into 
the  chamber  E,  where  it  deposits  a  mercurial  dust,  whicli 
yields  by  filtration  an  additional  quantity  of  liquid  mcrcur}^, 
and  a  residue  which  is  mixed  with  clay  and  pounded  ore,  and 
returned  to  the  furnace  in  the  manner  above  mentioned.  The 

heating  of  the   furnace  is 


Fig  17. 


Fig.  18. 


continued  for  twelve  or 
thirteen  hours :  it  is  then 
left  to  cool  for  three  or  four 
days,  after  which  it  is  cleared 
out  and  arranged  for  another 
operation. 

In  the  duchy  of  Deux 
Ponts,  a  mixture  of  cin- 
nabar iind  limestone  is 
heated  to  redness  in  retorts 
of  earthenware  or  cast-iron 
placed  side  by  side  in  an 
oblong     furnace    (fig.   18), 


rURinCATION    OF    MERCURY.  295 

and  provided  witli  receivers  containing  a  certain  quantity  of 
water.  Sulphide  of  calcium  and  sulphate  of  lime  are  then 
formed,  and  the  mercury  is  evolved  in  vapour,  which  con- 
denses in  the  receivers. 

At  Horzowitz,  in  Bohemia,  a  mixture  of  cinnabar  and 
smithy-scales  is  placed  in  iron  dishes,  which  are  attached  one 
above  the  other  by  the  centres  of  their  bases  to  a  vertical  iron 
axis,  and  covered  with  an  iron  receiver,  closed  at  top  and 
dipping  into  water  at  the  bottom.  The  upper  part  of  the 
receiver  is  surrounded  by  the  furnace,  and  imparts  its  heat 
to  the  dishes,  from  which  the  mercury  rises  in  vapour  and 
collects  in  the  water  below. 

The  mercury  of  commerce  is  generally  very  pure;  it  is 
sometimes,  however,  contaminated  with  foreign  metals,  and 
in  that  case  its  fluidity  is  remarkably  impaired. 

Mercury  may  be  purified  by  distilling  it  from  half  its 
weight  of  iron- turnings,  or  by  digesting  it  with  a  small  quan- 
tity of  nitric  acid,  or  with  a  solution  of  corrosive  sublimate, 
which  rids  it  of  metals  more  oxidable  than  itself.  The 
purification  may  also  be  effected  by  agitating  the  mercury 
with  a  small  quantity  of  solution  of  sesquichloride  of  iron. 
Pure  mercury  should  leave  no  residue  when  dissolved  in  nitric 
acid,  evaporated,  and  ignited;  when  made  to  run  down  a 
slightly  inclined  surface,  it  should  retain  its  round  form,  and 
not  drag  a  tail;  and  when  agitated  in  a  bottle  with  dry  air, 
it  should  not  yield  any  black  powder. 

Mercury  is  liquid  at  ordinary  temperatures.  Its  colour  is 
white,  with  a  shade  of  blue  when  compared  with  that  of 
silver,  and  it  has  a  high  metallic  lustre.  At  39°  or  40°  below 
zero,  it  becomes  solid,  and  crystallises  in  regular  octohedrons. 
According  to  M.  Kupffer,  the  density  of  mercuiy  at  39  2°  is 
13-5886;  at  62-6'^,  13'5569;  and  at  78-8°,  13-535  (according 
to  Kopp,  it  is  13-595  at  39-2°).  In  the  solid  state,  its  density 
is  about  14-0.  Mercury  boils  at  662°,  forming  a  colourless 
vapour,  the  density  of  which  was  observed,  by  Dumas,  to 


296  MERCURY. 

be  6976 ;  the  theoretical  density  is  6930.  Mercury  emits  a 
sensible  vapour  between  68°  and  80°,  but  not  under  20° 
{Faraday).  When  heated  near  its  boiling  point,  mercury 
a])sorbs  oxygen  from  the  air,  and  forms  crystalline  scales  of 
the  red  oxide.  It  is  not  affected  by  boiling  hydrochloric  or 
dilute  sulphuric  acid,  but  is  readily  dissolved  by  dilute  nitric 
acid.  This  metal  never  dissolves  in  hydrated  acids  by  sub- 
stitution for  hydrogen.  Mercury  combines  with  oxygen  in 
two  proportions,  forming  the  black  oxide,  IIg20,  and  the  red 
oxide,  composed  of  single  equivalents,  HgO,  both  of  which 
are  bases.  According  to  these  formula;,  the  equivalent  of 
mercury  is  assumed  to  be  100 ;  but  whether  it  should  be 
this  number  or  a  multiple  of  it  by  2,  no  certain  means  exist 
of  deciding,  while  we  are  in  ignorance  of  any  isomorphous 
relation  of  mercury  with  the  magnesian  metals. 


MERCUROUS    COMPOUNDS. 

Dioxide  of  mercury  [black  oxide),  Mercurous  oxide,  Hg20, 
208  or  2600.  —  This  oxide  is  obtained  by  the  action  of  a  cold 
solution  of  potash,  used  in  excess,  upon  calomel.  The  sub- 
stances should  be  mixed  briskly  together  in  a  mortar,  in 
order  that  the  decomposition  may  be  as  rapid  as  possible, 
and  the  oxide  be  left  to  dry  spontaneously  in  a  dark  place. 
Mr.  Donovan  finds  these  precautions  necessary,  from  the  dis- 
position of  this  oxide  to  resolve  itself  into  metallic  mercury 
and  the  higher  oxide.  The  decomposition  of  mercurous 
oxide  is  promoted  by  elevation  of  temperature,  and  by  ex- 
posure to  light. 

Mercurous  oxide  is  a  black  powder,  whose  density  is  10*69 
(J.  Herapath) ;  it  unites  with  acids  and  forms  salts.  Its  soluble 
salts  are  all  partially  decomposed  by  pure  water,  which  com- 
bines with  a  portion  of  their  acid,  and  throws  down  a  subsalt 
containing  an  excess  of  oxide.  They  are  precipitated  black 
by  hydrosulphuric  acid  and  alkaline  sulphides.     Caustic  alka- 


MERCUROUS    COMPOUNDS.  297 

lies  throw  down  a  black  precipitate  of  mercurous  oxide.  The 
alkaline  carbonates  precipitate  white  mercurous  carbonate, 
which  soon  turns  black  from  decomposition.  Carbonate  of 
baryta  also  decomposes  mercurous  salts,  forming  a  mercuric 
salt  which  remains  in  solution,  and  a  precipitate  of  metallic 
mercury.  Mercurous  salts  are  decomposed  by  hydrochloric 
add  and  soluble  chlorides,  with  precipitation  of  calomel  as  a 
white  powder,  a  property  by  which  they  are  distinguished 
from  the  salts  of  the  red  oxide  of  mercury.  In  very  dilute 
solutions,  only  an  opalescence  is  produced.  The  precipitate 
turns  black  when  treated  with  potash  or  ammonia.  Mer- 
curous salts  form  with  phosphate  of  soda  a  white  precipitate 
of  mercurous  phosphate,  and  with  alkaline  chromateSy  a  brick- 
red  precipitate  of  mercurous  chromate.  Oxalic  acid  and 
alkaline  oxalates  form  a  white  precipitate  of  mercurous  oxalate. 
Ferrocyanide  of  potassium  produces  a  thick  white  precipitate, 
Siiid  ferricyanide  of  potassium  a  red-brown  precipitate.  Tinc- 
ture of  galls  yields  a  brownish-yellow  precipitate. 

The  salts  of  this,  and  also  of  the  red  oxide,  are  reduced  to 
the  metallic  state  by  copper  and  the  more  oxidable  metals, 
and  by  the  proto-compounds  of  tin ;  also  by  phosphorous  and 
sulphurous  acids.  The  precipitated  mercury  often  takes  the 
form  of  a  grey  powder,  in  which  no  metallic  globules  are  per- 
ceptible, and  remains  in  this  condition  while  moist.  Mercury 
in  this  divided  state  possesses  the  medicinal  qualities  of  the 
milder  mercurials,  and  has  often  been  mistaken  for  black 
oxide.  To  obtain  precipitated  mercury,  equal  weights  of 
crystallised  protochloride  of  tin  (salt  of  tin)  and  corrosive 
sublimate  may  be  dissolved,  the  first  in  dilute  hydrochloric 
acid  and  the  second  in  hot  water,  and  the  solutions  mixed, 
with  stirring.  The  salt  of  tin  takes  up  all  the  chlorine  of  the 
corrosive  sublimate,  becoming  bichloride  of  tin,  which  remains 
in  solution,  while  the  mercury  is  liberated,  and  forms  so  fine 
a  precipitate,  that  it  requires  several  hours  to  subside.  It 
may  be  washed  by  affusion  of  hot  water  and  subsidence,  and 


298  MERCURY. 

slightly  drained  on  a  filter,  but  not  allowed  to  dry.  There 
can  be  no  doubt  that  it  is  in  this  divided  state,  and  not  as  the 
black  oxide,  that  mercury  is  obtained  by  trituration  with  fat, 
turpentine,  syrup,  saliva,  &c.,  in  many  pharmaceutical  pre- 
parations. 

Bisulphide  of  mercury ^  HgjS,  is  obtained,  as  a  black  pre- 
cipitate, by  the  action  of  hydrosulphuric  acid  on  a  solution  of 
mercurous  nitrate  or  upon  calomel.  This  sulphide  is  decom- 
posed by  a  gentle  heat,  and  resolved  into  globules  of  mercury 
and  the  higher  sulphide. 

Dichloride  of  mercury y  Mercurous  chloride,  Calomel,  Hg2Cl, 
235-5  or  2913-75.  —  A  variety  of  processes  are  given  for  the 
preparation  of  this  remarkable  substance.  It  may  be  obtained 
in  the  humid  way,  by  digesting  IJ  parts  of  mercury  with 
1  part  of  pure  nitric  acid,  of  density  from  1*2  to  1-25,  till  the 
metal  ceases  to  dissolve,  and  the  liquid  has  begun  to  assume 
a  yellow  tint.  A  solution  is  also  prepared  of  1  part  of  cldoride 
of  sodium  in  32  parts  of  distilled  water,  to  which  a  certain 
quantity  of  hydrochloric  acid  is  added ;  and  this,  when  heated 
to  near  the  boiling  point,  is  mixed  with  the  mercurial  salt. 
The  mercury  takes  up  the  chlorine  of  the  common  salt,  and 
the  subehloride  of  mercury  formed  precipitates  as  a  white 
powder,  while  the  nitric  acid  and  oxygen  are  given  up  by  the 
mercury  to  the  sodium,  which  becomes  nitrate  of  soda : 

NaCl  +  HgaO  .  NO5  =  Hg2Cl  +  NaO  .  NO5. 

The  excess  of  acid  in  this  process  is  intended  to  prevent  the 
precipitation  of  any  subnitrate  of  mercury,  which  the  dilution 
of  the  nitrate  of  mercury,  on  mixing  the  solutions,  might 
occasion.  Calomel  is  also  obtained  by  rubbing  together,  in  a 
mortar,  4  parts  of  protochloride  of  mercury  (corrosive  sub- 
limate) with  3  parts  of  running  mercury.  The  mixture  is 
afterwards  introduced  into  a  glass  balloon,  and  sublimed  by  a 
heat  gradually  increased.  Here  the  protochloride  of  mercury 
combines  with  mercury,  and  the  dichloride  is  produced.     The 


MERCUROUS   COMPOUNDS.  299 

same  result  is  obtained  by  mixing  mercuric  sulphate  witb  as 
much  mercury  as  it  already  contains,  and  about  one-third  of 
its  weight  of  chloride  of  sodium,  and  subliming  the  mixture. 
The  vapour  of  the  dichloride  of  mercury,  in  these  sublima- 
tions, is  advantageously  condensed  by  conducting  it  into  a 
vessel  containing  hot  water;  the  vapour  of  the  water  then 
condenses  the  salt  in  an  extremely  fine  and  beautifully  white 
powder.  The  product  of  this  operation  is  recommended  by 
its  purity,  as  well  as  by  its  minute  division ;  for  the  water 
dissolves  out  all  the  protochloride  of  mercury  by  which  the 
dichloride  is  accompanied.  It  appears  that  whenever  the 
dichloride  is  sublimed,  a  small  portion  of  it  is  resolved  into 
mercury  and  the  protochloride.  As  the  calomel  usually  con- 
denses in  a  solid  cake,  it  must,  to  prepare  it  for  medical  use, 
be  reduced  to  a  fine  powder,  and  washed  with  hot  water  to 
remove  the  soluble  chloride. 

Dichloride  of  mercury  is  obtained  by  sublimation,  in  four- 
sided  prisms,  terminated  by  summits  of  four  faces.  When 
the  solid  cake  is  finely  pounded,  the  salt  acquires  a  yellow 
tinge.  The  density  of  this  salt  in  the  solid  condition  is  6'5 ; 
in  the  state  of  vapour  8350.  One  volume  of  the  vapour  con- 
tains one  volume  of  vapour  of  mercury  and  half  a  volume  of 
chlorine.  This  salt  is  so  very  sparingly  soluble  in  water,  that 
when  mercurous  nitrate  is  added  to  hydrochloric  acid  diluted 
even  with  250,000  times  its  weight  of  water,  a  sensible  pre- 
cipitate of  dichloride  of  mercury  appears.  When  boiled  for  a 
long  time  in  hydrochloric  acid,  this  salt  is  resolved  into  proto- 
chloride of  mercury  which  dissolves,  and  mercury  which  is 
reduced. 

Action  of  ammonia  on  dichloride  of  mercury. —  The  dry 
dichloride  was  found  by  Rose  to  absorb  an  equivalent  of 
ammonia,  and  to  become  black.  Exposed  to  air,  the  com- 
pound loses  its  ammonia,  and  the  dichloride  of  mercury 
recovers  its'  white  colour.      This  ammoniacal  compound  is 

VOL.  II,  Y 


300  MERCURY. 

HgjCl.NHg,  and  may  be  regarded  as         3„g  iq\^  ^i^at  is,  as 

dichloride  of  mercury  in  -which  1  eq.  of  mercury  is  replaced 

by  mercurammonium,  NHgHg.  Or  again,  if  we  suppose  the 
mercurous  salts  to  contain,  not  two  distinct  atoms,  but  a 
double  atom  of  mercury  (Hg'  =  Hgj),  this  double  atom  being 
the  equivalent  of  one  atom  of  hydrogen  —  thus,  calomel 
=  Hg'Cl  j  black  oxide  of  mercury  =  Hg'O,  &c., —  then  the 
ammoniacal   compound  HgjCl.NHg   may  be    regarded    as 

chloride  of  mercurosammonium,  NHgHg' .  CI,  or  chloride  of 
ammonium  in  which  one  eq.  H  is  replaced  by  a  double  atom 
of  mercury. 

When  calomel  is  digested  in  aqueous  ammonia,  it  turns 
black,  and  was  found  by  Kane  to  be  converted  into  mercurous 
amido-chloride,  Hg2Cl.Hg2NH2,  sal-ammoniac  being  formed 
at  the  same  time  : 

SHg^Cl  +  2NH3  =  Hg2Cl.Hg2NH2  +  NH4CI. 
This  compound  may  also  be  regarded  as  chloride  of  bimercu- 


7'osammonium,  NH2Hg'2 .  CI.  It  is  not  altered  by  boiling 
water ;  when  quite  dry,  it  is  of  a  grey  colour. 

Dibromide  of  inercury,  Mercurous  bromide,  Hg2Br,  is  a 
white  insoluble  powder,  resembling  in  all  respects  the  di- 
chloride, and  formed  in  similar  circumstances.  A  boiling 
solution  of  bromide  of  strontium  was  found  by  Loewig  to  dis- 
solve three  equivalents  of  dibromide  of  mercury,  of  which  one 
equivalent  precipitated  during  the  cooling  of  the  solution. 
When  the  filtered  solution  was  evaporated,  it  deposited  a  salt  in 
small  crystals,  containing  SrBr.  2Hg2Br.  These  crystals  were 
decomposed  by  pure  water,  and  resolved  into  the  insoluble 
dibromide,  Hg2Br,  and  a  double  salt,  SrBr .  rig2Br,  which 
dissolved  easily,  and  crj'stallised  by  evaporation. 

Diniodide  of  mercury,  Mercurous  iodide,  HgjT,  is  obtained 
by  precipitation  as  a  green  powder,  which  is  red  when  heated. 
It  is  also  formed  by  triturating  mercury  and  iodine  together 


MERCUROUS    COMPOUNDS.  301 

in  a  mortar,  with  a  few  drops  of  alcohol,  in  the  proportion  of 
2  eq.  of  the  former  to  1  eq.  of  the  latter. 

No  dicyanide  of  mercury  exists ;  and  it  is  doubtful  whether 
a  difluoride,  corresponding  with  the  dioxide,  has  been  formed. 

Mercurous  carbonate,  Carbonate  of  black  oxide  of  mercury, 
Hg*02.C02,  precipitates  as  a  white  powder,  when  an  alkaline 
carbonate  is  added  to  the  nitrate  of  the  same  oxide.  The 
precipitate  becomes  grey  when  the  liquid  containing  it  is 
boiled,  and  carbonic  acid  escapes.  This  carbonate  is  soluble 
both  in  carbonic  acid  water,  and,  to  a  slight  extent,  in  an 
excess  of  alkaline  carbonate. 

Mercurous  sulphate,  Sulphate  of  black  oxide  of  mercury, 
Hg20.S03;  248  or  3100.  — This  salt  is  obtained  by  digesting 
1  part  of  mercury  in  1^  parts  of  sulphuric  acid,  avoiding  a 
high  temperature,  and  interrupting  the  process  as  soon  as  all 
the  mercury  is  converted  into  a  white  salt.  It  is  also  pre- 
cipitated when  sulphuric  acid  is  added  to  a  solution  of  mer- 
curous nitrate.  The  salt  may  be  washed  with  a  little  cold 
water.  It  crystallises  in  prisms,  and  requires  500  times  its 
weight  of  cold  and  300  of  hot  water  to  dissolve  it.  With 
aqueous  ammonia  this  salt  forms  a  dark  grey  powder,  con- 
taining ammonia  or  its  elements. 

Mercurous  seleniate. — Aqueous  solutions  of  seleniate  of  soda 
and  mercurous  nitrate  form  a  white  precipitate,  probably 
consisting  of  the  neutral  salt,  Hg20 .  SeOg,  which,  however, 
gradually  turns  yellow  during  washing,  and,  when  dried  at 
100°,  is  found  to  be  reduced  to  6Hg20  .SSeOg  (Komer). 

Mercurous  selenite. — The  neutral  salt  Hg20.Se02  is  found 
native  as  onofrite,  a  yellow  earthy  mineral,  occurring,  together 
with  horn-quicksilver  and  native  mercury,  at  San  Onofrio,  in 
Mexico.  It  is  also  obtained  by  double  decomposition  as  a 
white  powder,  which  melts  at  356°,  and  when  heated  above 
that  point,  is  converted  into  a  brick-red,  opaque,  crystalline 
mass  of  the  salt  3Hg20.4Se02  (Kohler).* 

*  Pogg.  Ann.  Ixxxix.  146. 

Y  2 


302  MERCURY. 

Mercurom  nitrates,  Nitrates  of  black  oxide  of  mercury. — 
The  neutral  nitrate  is  obtained  when  mercury  is  dissolved  in 
an  excess  of  cold  nitric  acid  :  it  crystallises  readily  in  trans- 
parent rhombs.  It  is  soluble  with  heat  in  a  small  quantity 
of  water,  but  is  decomposed  by  a  large  quantity  of  water,  and 
an  insoluble  subsalt  formed,  unless  nitric  acid  be  added  to  the 
water.  The  formula  of  this  salt  is  Hg20.N05  +  2H0.  A 
subnitrate  is  formed  when  the  black  oxide  is  dissolved  in  a 
solution  of  the  preceding  salt,  or  when  an  excess  of  mercury 
is  digested  in  diluted  nitric  acid  at  the  usual  temperature. 
It  crystallises  readily  in  white,  opaque  rhombic  prisms, 
which  contain,  according  to  both  G.  Mitscherlich  and 
Kane,  3Hg20.2N05 -f  3H0;  or,  according  to  Marignac, 
4Hg20.3N03  +  HO.  This  salt  was  observed  by  G.  Mit- 
scherlich to  be  dimorphous.  "When  dissolved  by  dilutp  nitric 
acid,  it  yields  the  neutral  salt.  The  subnitrate  is  soluble  in 
a  little  water,  but  when  treated  with  a  large  quantity,  it  leaves 
imdissolvcd,  like  the  neutral  nitrate,  a  white  powder,  which 
retains  its  colour  so  long  as  the  supernatant  liquid  is  acid,  Ijut 
becomes  yellow  when  washed  with  water.  The  yellow  sub- 
nitrate  of  mercury  was  found  to  contain  2lIg.2O.NO5  +  HO 
(Kane).  Another  subnitrate,  containing,  according  to  Ma- 
rignac, SHgjO.SNOg -f  2H0,  is  obtained  by  boiling  the 
solution  or  the  mother-liquor  of  the  neutral  or  the  sesqui- 
basic  nitrate  with  excess  of  mercury  for  several  hours.  This 
salt  crystallises  in  colourless  or  slightly  yellow  crystals,  derived 
from  an  unsymmetrical  oblique  prism ;  it  appears  to  be  the 
most  stable  of  all  the  mercurous  subnitrates.  When  very 
dilute  ammonia  is  added  to  the  preceding  soluble  nitrates, 
without  neutralising  the  whole  acid,  a  velvety  black  precipi- 
tate falls,  known  as  Hahnemann's  soluble  mercury.  This  salt 
contains,  according  to  the  analysis  of  C.  G.  Mitscherlich, 
SHgjO.NOg  +  NH3.  But  when  pains  were  taken  to  avoid 
decomposition  of  the  salt  in  washing  it,  its  composition  was 
found  by  Kane  to  be  2IIg20.N05  +  NH3.      Bibasic  mer- 


MERCURIC    COMPOUNDS.  303 

curous  nitrate,  mixed  in  solution  with  nitrate  of  lead,  yields  a 
crystalline  double  salt,  containing  2(PbO.N05)  +  2Hg20.N05; 
and  similar  double  salts  with  the  nitrates  of  baryta  and  stron- 
tia  (G.  Staedeler). 

Mercurous  acetate,  HggO  .  C4H3O3,  falls  when  acetic  acid, 
or  an  acetate,  is  added  to  the  iiitrate,  in  crystalline  scales  of 
a  pearly  lustre.  It  is  anhydrous,  and  sparingly  soluble  in 
water. 


MERCURIC    COMPOUNDS. 

Protoxide  of  mercury  [red  oxide).  Mercuric  oxide,  HgO, 
108  or  1351. — This  compound  is  formed,  as  described,  by 
the  oxidation  of  mercury  at  a  high  temperatm*e,  or  by  heat- 
ing the  nitrate  of  mercmy  till  all  the  nitric  acid  is  expelled, 
and  the  mass,  calcined  almost  to  redness,  no  longer  emits 
vapoui-s  of  nitric  oxide.  As  prepared  by  the  latter  process, 
protoxide  of  mercmy  forms  a  brilliant  orange-red  powder, 
crystallised  in  plates,  and  having  the  density  11*074.  It  is 
very  dark  red  at  a  high  temperature,  but  becomes  paler  as  it 
cools.  When  reduced  to  a  line  powder,  it  becomes  yellow, 
like  litharge,  without  any  shade  of  red.  It  was  found  by 
]\Ir.  Donovan  to  be  soluble  to  a  small  extent  in  water,  form- 
ing a  solution  which  has  a  slight  alkaline  reaction.  If  con- 
taminated with  nitric  acid,  it  gives  off  nitrous  fumes  when 
heated  in  a  glass  tube,  and  forms  a  yeUow  sublimate  of  sub- 
nitrate.  This  oxide  is  known  in  pharmacy  as  red  precipitate, 
Tiie  same  compound  is  obtained  by  precipitation,  when  a 
solution  of  corrosive  sublimate  is  mixed  with  an  excess  of 
caustic  potash ;  it  then  forms  a  dense  powder  of  a  lemon- 
yellow  colour.  It  is  necessary  to  use  the  potash  in  excess, 
otlierwise  a  dark  brown  oxychloride  is  formed.  The  preci- 
pitated oxide  parts  with  a  little  moistiu*e  when  gently  heated, 
but  does  not  change  in  appearance.  This  yellow  precipitated 
oxide  differs  in  some  respects  from  the  red  oxide ;  it  combines 

T   3 


304  MERCURY. 

in  the  cold  with  oxalic  acid,  whereas  the  red  oxide  does  not ; 
it  is  converted  into  black  oxychloride  by  the  action  of  an 
alcoholic  solution  of  mercuric  chloride,  which  has  no  action 
on  the  red  oxide,  and  it  is  attacked  by  chlorine  much  more 
readily  than  the  latter.  At  a  red  heat,  the  oxide  of  mer- 
cury is  entirely  volatilised  in  the  form  of  oxygen  and  metallic 
mercury;  the  same  decomposition  takes  place  more  slowly 
under  the  influence  of  light.  The  oxide  detonates  when 
heated  with  sulphur,  and  converts  chlorine  into  hypochlorous 
acid. 

The  salts  of  mercuric  oxide,  when  they  do  not  contain  a 
coloured  acid,  are  colourless  in  the  neutral,  and  yellow  in 
the  basic  state.  They  have  a  disagreeable  metallic  taste,  and 
act  as  violent  acrid  poisons.  Some  of  them,  e.  g.  the  nitrate 
and  sulphate,  are  resolved  by  water  into  a  soluble  acid  salt, 
and  an  insoluble  basic  salt.  From  their  aqueous  solutions 
the  mercury  is,  for  the  most  part,  precipitated  in  the  metallic 
state  by  the  same  substances  as  from  mercurous  salts ;  but 
the  complete  reduction  of  the  mercury  is  often  preceded  by 
the  formation  of  a  mercurous  salt :  such,  for  example,  is  the 
action  of  phosphorous  acid,  sulphurous  acid,  protochloride  of 
tin,  metallic  copper,  &c.  Gold  does  not  by  itself  reduce 
mercury  from  its  salts ;  but  if  a  drop  of  a  mercm'ic  solution 
be  laid  on  a  piece  of  gold,  and  a  bar  of  zinc,  tin,  or  iron  be 
brought  in  contact  with  the  moistened  surface,  an  electrolytic 
action  is  set  up,  and  the  gold  becomes  amalgamated  at  the 
point  of  contact.  Hydrosul/jhuric  acid  and  alkaline  sulphides, 
added  in  excess  to  mercuric  salts,  throw  down  a  black  pre- 
cipitate of  mercuric  sulphide,  insoluble  in  strong  nitric  acid. 
If,  however,  the  quantity  of  the  re-agent  added  is  not  suffi- 
cient for  complete  decomposition,  a  white  precipitate  is  formed 
consisting  of  a  compound  of  mercuric  sulphide  with  the 
original  salt,  and  often  coloured  yellow  or  brown  by  excess  of 
the  sulphide :  this  re-action  is  quite  peculiar  to  mercuric  salts. 
Ammonia  and  carbonate  of  ammonia  form  white  precipitates. 


MERCURIC    COMPOUNDS.  305 

generally  consisting  of  a  compound  of  the  mercuric  salt 
with  amide  of  mercury.  The  fixed  alkalies  throw  down  a 
yellow  precipitate  of  mercuric  oxide  (not  hydrated),  insoluble 
in  excess.  If,  however^  the  solution  contains  a  large  quantity 
of  free  acid^  no  red  precipitate  is  formed,  or  only  a  slight  one 
after  a  considerable  time.  Monocarbonate  of  potash  or  soda 
throws  down  red-brown  mercuric  carbonate.  But  if  any 
ammoniacal  salt  is  present  in  the  solution,  the  fixed  alkalies 
and  their  carbonates  throw  down  the  white  precipitate  above 
mentioned.  Bicarbonate  of  potash  or  soda  also  gives  a  brown- 
red  precipitate,  with  mercuric  nitrate  or  sulphate ;  but  with 
the  chloride  it  forms  a  white  precipitate  which  afterwards 
turns  red.  The  carbonates  of  baryta,  strontia,  and  lime 
precipitate  mercuric  oxide  from  the  solutions  of  the  sulphate 
and  nitrate,  but  not  from  the  chloride.  Phosphate  of  soda 
throws  down  white  mercuric  phosphate  from  the  sulphate 
and  nitrate,  but  not  from  the  chloride.  Chromate  of  potash 
forms  a  yellowish  red  precipitate.  Ferrocyanide  of  potassium 
forms,  in  solutions  not  too  dilute,  a  white  precipitate  which 
gradually  turns  blue.  Tincture  of  galls  forms  an  orange- 
yellow  precipitate  with  all  mercuric  solutions  except  the 
chloride.  Iodide  of  potassium  produces  a  scarlet  precipitate 
of  mercuric  iodide,  soluble  in  excess  either  of  the  mercuric 
salt  or  of  iodide  of  potassium. 

When  aqueous  ammonia  is  digested  for  several  days 
upon  precipitated  oxide  of  mercury,  the  latter  is  converted 
into  a  yellowish  white  powder,  which  Kane  regards  as 
2HgO  .  HgNH2  +  3HO,  or  as  a  hydrated  compound  of  amide 
and  oxide  of  mercury,  which  may  be  called  oxyamide  of  mer- 
cury. According  to  Millon*,  on  the  other  hand,  its  compo- 
sition is  4IigO.NH3  +  2HO,  or  rather  3HgO .  HgNH2.HO 
-I-  2H0.  This  substance,  when  placed  in  vacuo  over 
quick  lime,  gives  off  2  eq.  water,  turns  brown,  and  in  that 
state  undergoes  no  further  alteration  by  exposure  to  the  air 

*  Compt.  rend.  xxi.  826. 
Y  4 


306  MERCURY. 

at  ordinary  temperatures;  but  between  100°  and  130°  C,  it 
gives  off  a  third  atom  of  water  and  is  reduced  to  the  anhy- 
drous compound  3HgO  .  HgNHg.  The  yellow  hydrated  com- 
pound rapidly  absorbs  carbonic  acid  from  the  air,  and  turns 
white.  Dilute  potash  has  no  action  upon  it ;  but  very  strong 
potash,  at  a  boiling  heat,  decomposes  it,  with  evolution  of 
ammonia.  The  brown  anhydrous  compound  resists  the  action 
of  aqueous  potash  even  at  the  boiling  heat,  but  is  decomposed  by 
fusion  with  hydrate  of  potash.  Oxyamide  of  mercury  is  a  power- 
ful base,  and  expels  ammonia  from  its  salts.  One  equivalent 
of  this  compound,  represented  by  the  formula  3HgO  .  HgNH^, 
saturates  1  eq.  of  sulphuric  acid,  nitric  acid,  &c. ;  thus  the 
sulphate  is  3HgO  .  HgNHa  .  SO3;  the  nitrate,  31IgO.IIgNH2. 
NO5  +  HO,  &c.  &c. 

Nitride  of  mercury ,  M er  cur  ammonia ,  NIIg3.  —  This  com- 
pound is  formed  by  passing  dry  ammoniacal  gas  over  precipi- 
tated mercuric  oxide  previously  well  washed  and  dried  : 

3Hg04-NH3^NHg3H-3HO. 

After  removing  the  excess  of  mercuric  oxide  by  dilute  ni- 
tric acid,  the  mercurammonia  is  obtained  in  the  form  of  a 
dark  flea-brown  powder,  which  explodes,  by  heat,  friction, 
percussion,  or  by  contact  with  oil  of  vitriol,  almost  as  violently 
as  iodide  of  nitrogen.  When  carefully  heated  with  hydrate 
of  potash,  it  is  decomposed  witliout  detonation,  yielding  am- 
moniacal gas  and  sublimed  metallic  mercury.  It  is  also 
decomposed  by  hydrochloric  acid,  sulphuric,  and  concentrated 
nitric  acid,  yielding  an  ammoniacal  and  a  mercuric  salt.  It 
may  be  regarded  as  ammonia  in  which  the  hj^drogen  is 
entirely  replaced  by  an  equivalent  quantity  of  mercury 
(Plantamour).* 

By  the  action  of  various  ammoniacal  salts  at  a  boiling  heat 
on  mercuric  oxide,  compounds  are  obtained  consisting  of 
nitride  of  mercury  combined  with  mercuric  salts  :  e.  g.  with 

*  Ann.  Cli.  Pliarm.  xl.  115. 


MERCURIC    COMPOUNDS.  307 

nitrate  of  ammoma,  the  compound  NHg3  +  2(3HgO  .  NO5)  is 
obtained ;  with  phosphate  of  ammonia,  the  compound  NHgg  + 
3HgO  .  PO5  +  3H0  ;  with  carbonate  of  ammonia,  the  com- 
pound 2(NHg3+  HgO  .  CO2  +  2HO)  +  HO  j  with  chromate  of 
ammonia,  the  compound  NHgg  .  HgO  .  2HO  +  4(HgO.Cr03), 
which  when  treated  with  ammonia  is  converted  into  NHg3  + 
HgO  .  Cr03  +  2HO;  with  acetate  of  ammonia,  the  compound 
NHg3  +  C^H3Hg04  +  4HO,  &c.  &c.  (Hirzel)  * 

Protosulphide  of  mercury,  Mercuric  sulphide,  Cinnabar, 
HgS;  116  or  1450.  —  This  is  the  common  ore  of  mercury, 
and  sometimes  occurs  crystallised,  forming  a  beautiful  ver- 
milion. It  is  prepared  artificially  by  fusing  one  part  of  sul- 
phur in  a  crucible,  and  adding  to  it  by  degrees  six  or  seven 
parts  of  mercury,  stirring  it  after  each  addition,  and  covering 
it  to  preserve  it  from  contact  of  air,  when  it  inflames,  from 
the  heat  evolved  in  the  combination.  The  product  is  exposed 
to  a  sand-bath  heat,  to  expel  the  sulphur  uncombined  with 
mercury,  and  afterwards  sublimed  in  a  glass  matrass  at  a  red 
heat.  A  brilliant  red  mass  of  a  crystalline  structure  is  thus 
obtained,  which,  when  reduced  to  fine  powder,  forms  the 
lively  red  pigment  vermilion.  This  sulphide  is  black  before 
sublimation.  It  is  precipitated  black  also  when  hydrosul- 
phuric  acid  is  passed  through  a  solution  of  corrosive  sublimate, 
but  is  of  the  same  composition  in  both  states.  The  sulphide 
of  mercury,  however,  may  be  obtained  of  a  red  colour  without 
sublimation,  or  in  the  humid  way,  by  several  methods. 

Liebig  recommends  for  this  purpose  to  moisten  the  pre- 
paration called  white  precipitate,  recently  prepared,  with 
sulphide  of  ammonium,  and  allow  them  to  digest  together. 
The  black  sulphide  is  instantly  produced,  which  in  a  few 
minutes  passes  into  a  fine  red  cinnabar,  the  colour  of  which  is 
improved  by  digesting  it  at  a  gentle  heat  in  a  strong  solution 
of  hydrate  of  potash.  The  sulphide  of  ammonium  used  in 
this  experiment  is  prepared  by  dissolving  sulphur  to  saturation 

*  Ann.  Ch.  Pharm.  Ixxxiv.  258. 


308  MERCURY. 

in  hydrosulphate  of  ammonia.  Cinnabar  is  not  attacked  by 
sulphuric,  nitric  or  hydrocldoric  acid,  or  by  solutions  of  the 
alkalies,  but  is  dissolved  by  aqua-regia. 

Protochloride  of  mercury,  Mercuric  chloride,  Corrosive  sub- 
limate, 135-5  or  1693*75.  —  This  compound  may  be  formed  by 
dissolving  red  oxide  of  mercury  in  hydrochloric  acid,  or  by 
adding  hydrocldoric  acid  to  any  soluble  salt  of  that  oxide ;  but 
it  is  generally  prepared  in  a  different  manner.  Four  parts  of 
mercury  are  added  to  five  parts  of  sulphuric  acid,  and  the 
mixture  boiled  tiQ  it  is  converted  into  a  dry  saline  mass.  The 
mercuric  sulphate  thus  obtained  is  mixed  with  an  equal  weight 
of  common  salt,  and  heated  strongly  in  a  retort  by  a  sand- 
bath;  chloride  of  mercury  sublimes  and  condenses  in  the 
upper  part  and  neck  of  the  retort,  while  sulphate  of  soda 
remains  behind  with  the  excess  of  chloride  of  sodium.  The 
mercury  and  sodium  have  exchanged  places  in  the  salts : 
NaCl  +  HgO .  SO3  =  HgCl  +  NaO  .  SO3. 

Mercury,  when  heated  in  a  stream  of  chlorine  gas,  burns 
with  a  pale  flame,  and  is  converted  into  a  white  sublimate 
of  chloride.  The  salt  has  been  prepared  on  a  large  scale  in 
this  manner,  which  was  suggested  as  a  manufacturing  process 
by  Dr.  A.  T.  Thomson. 

The  sublimed  chloride  of  mercury  forms  a  crystalline  mass, 
the  density  of  which  is  6*5 ;  it  fuses  at  509°,  and  boils  at 
about  563°.  The  vapour  of  chloride  of  mercury  is  colourless, 
its  density  94.20,  one  volume  of  it  containing  1  volume  of 
mercury  vapour  and  1  volume  of  chlorine  gas.  This  salt  is 
soluble  in  16  parts  of  cold  and  in  3  parts  of  boiling  water,  in 
2}  parts  of  cold  and  in  1^  part  of  boiling  alcohol,  and  in 
3  parts  of  cold  ether.  It  is  not  decomposed  by  sulphuric  or 
nitric  acid;  is  largely  dissolved  by  the  latter,  and  also  by 
hydrochloric  acid.  It  is  obtained  by  sublimation  and  from 
solution  in  two  different  crystalline  forms.  The  solutions  of 
chloride  of  mercury  exposed  to  the  direct  rays  of  the  sun 


MERCURIC    COMPOUNDS.  309 

evolve  oxygen^  while  hydrochloric  acid  is  dissolved  and 
dichloride  of  mercury  precipitates.  The  decomposition  of 
this  salt  by  the  action  of  light  is  much  more  rapid  when 
the  solution  contains  organic  matter.  The  poisonous  ac- 
tion of  chloride  of  mercury,  which  is  scarcely  inferior  to 
that  of  arsenious  acid,  is  best  counteracted  by  liquid  albu- 
men, with  which  chloride  of  mercury  forms  an  insoluble  and 
inert  compound. 

Many  metals,  viz.  arsenic,  antimony,  bismuth,  zinc,  tin, 
lead,  iron,  nickel,  and  copper,  decompose  mercuric  chloride 
in  ^he  dry  way,  withdrawing  the  half  or  the  whole  of  its 
chlorine,  and  separating  calomel  or  metallic  mercury,  which 
latter  forms  an  amalgam  with  the  excess  of  the  other  metal. 
Arsenic  forms  terchloride  of  arsenic  and  a  brown  sublimate. 
An  intimate  mixture  of  3  pts.  antimony  and  1  pt.  corrosive 
sublimate,  well  pressed  into  a  glass,  becomes  hot  and  liquid 
in  the  course  of  half  an  hour,  and  on  the  application  of  heat 
yields  terchloride  of  antimony  and  metallic  mercury.  Tin 
heated  with  corrosive  sublimate  yields  a  distillate  of  bichlo- 
ride of  tin,  and  a  grey  residue  containing  calomel  and  proto- 
chloride  of  tin.  Many  metals  also  reduce  the  mercury  from 
the  aqueous  or  alcoholic  solution  of  the  chloride  (p.  306) .  Most 
metals  throw  down  calomel  together  with  the  mercury ;  but 
zinc,  cadmium,  and  iron  precipitate  nothing  but  mercury, 
zinc  being  thereby  converted  into  a  semi-fluid  amalgam,  and 
cadmium  forming  an  amalgam  which  crystallises  in  beautiful 
needles.  The  other  reactions  of  mercuric  chloride  in  solution 
have  been  already  described  (p.  306,  307.). 

Chloride  of  mercury  with  ammonia. — 1.  When  chloride  of 
mercury  is  gently  heated  in  a  stream  of  ammoniacal  gas,  the 
latter  is  absorbed,  and  the  compound  fuses  from  heat  evolved 
in  the  combination.  The  product  was  found  by  Rose  to  con- 
tain 2HgCl .  NH3.  This  compound  boils  at  590°,  and  may 
be  distilled  without  loss  of  ammonia;  it  is  decomposed  by 
water.  —  2.    Fusible  white  precipitate.      When  the   double 


310  MERCURY. 

chloride  of  mercury  and  ammonium,  called  sal  alembroth,  is 
precipitated  by  potash  in  the  cold,  a  white  powder  is  obtained, 
which  was  first  distinguished  by  Wohler  from  the  compound 
next  described ;  its  composition  may  be  expressed,  according 
to  Kane's  analysis,  by  the  formula  HgCl .  NH3.  The  same 
compound  is  also  formed  when  ammonia  is  added  to  a  solution 
of  sal-ammoniac,  the  liquid  brought  to  the  boiling  point,  and 
chloride  of  mercury  dropt  into  it  so  long  as  the  precipitate 
which  is  produced  is  redissolved.  The  compound  appears,  on 
the  cooling  of  the  solution,  in  small  crystals,  which  are 
garnet  dodecahedrons  (Mitscherlich) .  The  crystalline  form 
of  this  compound  belongs,  therefore,  to  the  regular  system, 
like  that  of  sal-ammoniac. 

3.  Mercuric  amido-chloride.  —  The  compound  known  as 
white  precipitate f  and  sometimes  infusible  white  jjrecipitatey  to 
distinguish  it  from  the  preceding,  is  formed  when  ammonia  is 
added  to  a  solution  of  chloride  of  mercury.  When  first  pro- 
duced, it  is  bulky  and  milk-white ;  it  is  decomposed  by  hot 
water  or  by  much  washing  with  cold  water,  and  acquires  a 
yellow  tinge.  Kane  has  shown  that  white  precipitate  is  free 
from  oxygen,  and  contains  nothing  but  the  elements  of  a 
double  chloride  and  amide  of  mercury,  and  represents  it  by 
the  formula  HgCl .  HgNH2.  White  precipitate  is  distin- 
guished from  calomel  by  solution  of  ammonia,  w  hich  does  not 
alter  the  former,  but  blackens  the  latter :  it  is  readily  dis- 
solved by  acids. 

4.  Nitrochloricle  of  mercury. —  Mitscherlich  has  observed 
that  when  white  precipitate  is  gradually  heated  in  a  metal 
bath,  and  the  heat  continued  for  a  long  time,  three  atoms  of 
it  give  off  two  atoms  of  ammonia  and  one  atom  of  chloride  of 
mercury,  while  a  red  matter  remains  in  crystalline  scales, 
having  much  the  appearance  of  red  oxide  of  mercury  pro- 
duced by  the  oxidation  of  the  metal  in  air,  and  containing 
two  atoms  of  cliloride  of  mercuiy  united  with  a  com- 
pound of  one  atom  of  nitrogen  and  three  atoms  of  mercury, 


WHITE    PRECIPITATE.  311 

2HgCl.NHg3.  He  concludes  that  the  atom  of  white  preci- 
pitate should  be  multiplied  by  three ;  its  decomposition  by 
the  heat  of  the  metal  bath  will  then  be  represented  by  the 
equation :  — 

3(HgCl .  HgNH2)  =  2HgCl .  NHgg  +  2NH3  +  HgCl. 

The  red  compound  is  itself  decomposed  by  a  temperature 
above  680°,  and  resolved  into  chloride  of  mercury,  mercury, 
and  nitrogen.  It  is  insoluble  in  water,  and  is  not  altered  in 
boiling  solutions  of  the  alkalies.  It  may  be  boiled  without 
change  in  diluted  or  concentrated  nitric  acid,  and  in  pretty 
concentrated  sulphuric  acid,  but  it  is  decomposed  and  dissolved 
when  boiled  in  the  most  concentrated  sulphuric  acid  or  in  hy- 
drochloric acid ;  no  gas  is  evolved,  but  ammonia  and  chloride 
of  mercury  are  found  in  the  acid  solution.  The  compound 
NHg3  is  not  isolated  by  passing  ammonia  over  the  heated 
red  compound.  Mercury  conducts  itself  in  these  compounds 
in  the  same  way  as  potassium  with  ammonia,  the  olive- 
coloured  substance  produced  by  the  action  of  dry  ammonia 
upon  potassium  being  the  amide  of  potassium,  3(K.NH2), 
and  the  plumbago-looking  substance  left  on  heating  the  amide 
of  potassium,  when  ammonia  escapes,  a  compound  of  nitrogen 
and  potassium,  NK3.* 

5.  When  white  precipitate  is  boiled  in  water,  it  is  changed 
into  a  heavy  canary-yellow  powder,  which  Kane  regards  as  a 
compound  of  the  amido-chloride  of  mercury  with  oxide  of 
mercury,  HgCl.HgNH2.2HgO.  Two  atoms  of  water  are 
decomposed  in  its  formation,  yielding  the  two  atoms  of  oxy- 
gen which  are  found  in  the  yellow  compound,  while  the  two 
atoms  of  hydrogen,  added  to  an  atom  of  chlorine  and  an  atom 
of  amidogen,  form  an  atom  of  hydrochlorate  of  ammonia, 
which  is  found  in  solution  : 

2  (HgCl .  HgNH^)  +  2H0  =  HgCl .  HgNH^ .  2HgO  +  NH^Cl. 

*  Mitscherlicli  in  Poggeudorff's  Annalen,  toI.  xxxix.  p.  409. 


313  MERCURY. 

Solutions  of  potash  and  soda  convert  white  precipitate  into 
the  same  yellow  substance,  while  a  metallic  chloride  is  formed 
and  ammonia  evolved  (Kane). 

The  five  compounds  just  described  may  be  regarded  as  salts 
of  metalloidal  radicals  formed  from  ammonium  (NHJ  in 
which  the  whole  or  part  of  *the  hydrogen  is  replaced  by  an 
equivalent  quantity  of  mercurj'.  Thus,  the  fusible  white 
precipitate,    HgCl.NHg,   may  be  regarded  as  a  chloride  of 

fTT 

mercurammonium, —Q\J^\^j^  •,    the   preceding   compound, 

SHgCl.NHg,  as  a  double  chloride  consisting  of  the  same 
compound  united  with  chloride  of  mercury,  namely  as 

ClHg  4-  Cl.N  I  TT^  .    similarly,  infusible  white  precipitate, 

{TT 
Ho-  * 

the  yellow  powder  obtained  by  boiling  this  compound  with 
water  is  a  chloride  of  tetramercurammoninm  combined  ydth 
two  atoms  of  water,  =  ClNIIg^  +  2H0 ;  and  the  red  com- 
pound, 2IIgCl.NHg3,  may  be  regarded  as  a  compound  of 
this  same  chloride  with  chloride  of  mercury,  namely  as 
ClHg.ClNHg^. 

Oxy chloride  of  mercury.  —  When  a  solution  of  corrosive 
sublimate  is  precipitated  by  potash  or  soda,  mercuric  oxide 
goes  down,  in  combination  with  a  portion  of  chloride,  as  a 
brown  precipitate,  unless  a  considerable  excess  of  alkali  be 
employed.  The  same  oxychloride  is  produced  by  an  alkaline 
carbonate;  but  a  double  carbonate  is  then  also  foiTned. 
Chloride  of  mercury  is  not  immediately  precipitated  by  the 
bicarbonates  of  potash  and  soda ;  and  hence  that  salt  may  be 
employed  to  detect  the  presence  of  a  neutral  alkaline  car- 
bonate in  these  bicarbonates.  This  oxychloride  may  also  be 
formed  by  passing  chlorine  through  a  mixture  of  ^vater  and 
oxide  of  mercury.  It  may  be  obtained  crystalline  and  of  a 
very  dark  colour,  almost  black,  by  mixing  corrosive  subli- 


CHLORIDES   OF    MERCURY.  313 

mate  with  chloride  of  lime,  and  boiling  the  liquid,  or  by 
treating  a  solution  of  corrosive  sublimate  with  bicarbonate  of 
potash,  and  allowing  the  solution  to  stand  in  an  open  vessel, 
when  carbonic  acid  gradually  escapes,  and  the  compound 
HgCl .  .4HgO  is  deposited.  This  oxychloride  is  decomposed 
by  a  moderate  heat,  chloride  of  mercury  subliming,  while  the 
red  oxide  remains. 

Sulpho chloride  of  mercury,  HgC1.2HgS. — When  hydro- 
sulphuric  acid  gas  is  passed  through  a  solution  of  chloride  of 
mercury,  the  precipitate  which  first  appears,  and  does  not 
subside  readily,  is  white ;  it  has  been  shown  by  Rose  to  be  a 
compound  of  chloride  and  sulphide  of  mercury.  This  sub- 
stance is  changed  entirely  into  sulphide  of  mercury,  when 
left  in  water  containing  hydrosulphuric  acid.  On  the  other 
hand,  precipitated  sulphide  of  mercury  digested  in  a  solution 
of  chloride  of  mercury,  takes  down  that  salt,  and  forms  the 
compound  in  question.  The  same  compound  may  be  formed 
in  the  dry  way,  by  fusing  protosulphide  of  mercury  (either 
black  or  red)  with  eight  or  ten  times  its  weight  of  corrosive 
sublimate,  in  a  sealed  tube,  and  dissolving  out  the  excess  of 
chloride  by  boiling  water ;  the  sulphochloride  then  remains 
in  the  form  of  a  dirty -white  powder  having  a  distinctly  crys- 
talline structure  (R.  Schneider).  Sulphide  of  mercury  com- 
bines likewise  with  the  bromide,  iodide,  fluoride,  and  nitrate 
of  mercury,  and  always  in  the  proportion  of  two  atoms  of  the 
sulphide  to  one  atom  of  the  other  salt. 

Double  salts  of  chloride  of  mercury. — Chloride  of  mercury 
was  found  by  M.  Bonsdorff"  to  combine  with  chloride  of  potas^ 
sium  in  three  different  proportions,  forming  a  series  of  salts  in 
which  the  chloride  of  potassium  remains  as  one  equivalent, 
while  the  chloride  of  mercury  goes  on  increasing.  They  are 
KCl.HgCl.HO,  which  crystallises  in  large  transparent  rhom- 
boidal  prisms ;  KCl .  2HgCl .  2H0  crystallising  in  fine  needle- 
like amianths;  and  KCl  +  4HgCl  +  4HO,  which  crystallises 
also  in  fine  needles.     Chloride  of  sodium  forms  only  one  com- 


314  MERCURY. 

pound,  NaCl .  2HgCl .  4H0,  which  crystallises  in  fine  regular 
hexahedral  prisms.  One  of  the  double  salts  of  chloride  of 
ammonium  has  long  been  known  as  sal  alembroth.  It  crystal- 
lises in  flattened  rhomboidal  prisms,  NH^Cl .  HgCl .  HO, 
and  is  isomorphous  with  the  corresponding  potassium  salt. 
When  exposed  to  dry  air,  it  gives  off  its  water  without  change 
of  form.  Kane  has  also  obtained  NH^Cl .  2HgCl,  and  the 
same  with  an  atom  of  water,  NH^Cl .  2IIgCl .  HO,  the  first 
in  a  rhomboidal  form,  and  the  second  in  long  silky  needles. 
All  these  double  chlorides  are  obtained  by  dissolving  their 
constituent  salts  together  in  the  proper  proportions.  The 
chlorides  of  barium  and  strontium  form  well-crystallised  com- 
pounds with  chloride  of  mei^curi/y  viz.  BaCl.  2HgCl.  4H0, 
and  SrCl .  2HgCl .  2H0.  Chloride  of  calcium  combines  in 
two  proportions  with  mercuric  chloride.  When  chloride  of 
mercury  is  dissolved  to  saturation  in  chloride  of  calcium, 
tetrahedral  crystals  separate  from  the  solution,  which  are 
tolerably  persistent  in  air,  and  contain  CaCl .  5HgCl .  8HO. 
After  the  deposition  of  these  crystals,  the  liquid  yields,  when 
evaporated  by  a  gentle  heat,  a  second  crop  of  large  prismatic 
crystals,  CaCl .  2HgCl.  6H0,  which  are  very  deliquescent. 
Chloride  of  magnesium  also  forais  two  salts,  MgCl.SHgCl. HO, 
and  MgCl .  HgCl .  GHO,  both  deliquescent.  Chloride  of  nickel 
gives  two  compounds,  one  of  which  crystallises  in  tetrahedrons, 
like  the  chloride  of  calcium  salt.  Chloride  of  manganese 
forms  a  compound  in  good  crystals,  MnCl .  HgCl .  4H0.  The 
chlorides  of  iron  and  zinc  form  similar  isomorphous  salts, 
FeCl .  HgCl .  HO,  and  ZnCl .  HgCl .  HO.  The  double  chlo- 
rides of  zinc  and  of  manganese  are  remarkable  in  one  respect, 
that  chloride  of  mercury  dissolved  by  them  in  excess  crystallises 
by  evaporation  in  fine  large  crystals,  such  as  cannot  be  obtained 
in  any  other  way.  The  chlorides  of  cobalt,  nickel,  and  copper 
form  similar  crystallisable  salts;  but  chloride  of  lead  does 
not  appear  to  form  a  double  salt  with  chloride  of  mercury. 
(Bonsdorff.) 


PROTIODIDE    OF    MERCURY.  315 

Mercuric  chloride  likewise  forms  definite  compounds  with 
alkaline  chromates.  A  hot  solution  of  equal  parts  of  mercuric 
chloride  and  bichromate  of  ammonia  deposits,  on  cooling, 
large  hexagonal  prisms,  of  a  splendid  red  colour,  containing 
NH4O .  2Cr03  +  HgCl  +  HO,  and  the  mother-liquor  deposits  a 
further  crop  of  red,  somewhat  needle-shaped  crystals,  contain- 
ing 3  (NH40.2Cr03) +HgCl.  (Richmond  and  Abel.*)  Mono^ 
chromate  of  potash  forms  with  mercuric  chloride  a  brick-red 
precipitate  of  mercuric  chromate ;  and,  on  evaporating  the 
filtered  liquid,  small  pale  red  crystals  are  obtained  of  a  double 
salt,  containing  KO  .  Cr03  +  HgCl.  A  solution  of  equivalent 
quantities  of  mercuric  chloride  and  bichromate  of  potash  yields 
beautiful  red  pointed  crystals,  containing  KO .  2Cr03  +  HgCl. 
(Darby.t)  On  mixing  the  cold  saturated  aqueous  solutions 
of  acetate  of  copper  and  mercuric  chloride,  and  leaving  the 
mixture  to  evaporate,  deep  blue,  concentric,  radiated  hemi- 
spheres are  obtained,  containing  CuO  .  C4H3CUO4  +  HgCl. 
(Wohler  and  Hutteroth.)t 

Protobromide  of  mercury ,  Mercuric  bromide,  HgBr;  180  or 
2250. — This  salt  is  obtained  by  treating  mercury  with  water 
and  bromine.  It  is  colourless,  soluble  in  water  and  alcohol, 
and  when  heated,  fuses  and  sublimes,  exhibiting  a  great  ana- 
logy to  chloride  of  mercury  in  its  properties.  Its  density  in 
the  state  of  vapour  is  12370.  Bromide  of  mercury  forms  a 
similar  compound  with  sulphide  of  mercury  HgBr .  2HgS, 
which  is  yelloAvish.  It  was  also  combined,  by  BonsdorfF,  with 
a  variety  of  alkaline  and  earthy  bromides.  Bromide  of  mer- 
cury combines  with  half  an  equivalent  of  ammonia,  in  the 
dry  way,  and  also  gives,  with  solution  of  ammonia,  a  white 
precipitate,  analogous  to  that  derived  from  chloride  of  mer- 
cury. 

Protiodide  of  mercury,  mercuric  iodide,  Hgl,  226 '36  or 


*  Chem.  Soc.  Qu.  J.  iii.  202.  f  Chem.  Soc.  Qu.  J.  i.  24. 

X  Ann.  Ch.  Pharni.  lui.  142. 

VOL.  II.  Z 


316  MERCURY. 

2829*5. — Falls  as  a  precipitate  of  a  fine  scarlet  colour,  wlieu 
iodide  of  potassium  is  added  to  a  solution  of  chloride  of  mer- 
cury. It  may  also  be  obtained  by  triturating  its  constituents 
together,  in  the  proper  proportion,  ^nth  a  few  drops  of  alcohol. 
To  procure  it  in  crystals,  Mitscherlich  dissolves  iodide  of  mer- 
cury to  saturation,  in  a  hot  concentrated  solution  of  the  iodide 
of  potassium  and  mercury,  and  allows  the  solution  to  cool 
gradually.  When  heated  moderately,  mercuric  iodide  becomes 
yellow ;  at  a  higher  temperature,  it  fuses  and  sublimes,  con- 
densing in  rhomboidal  plates  of  a  fine  yellow  colour.  The 
forms  of  the  red  and  yellow  crystals  are  totally  different,  so 
that  the  change  of  colour  is  due  to  the  dimorphism  of  mer- 
curic iodide.  The  yellow  crystals  generally  return  gradually 
into  the  red  state  when  cold ;  and  this  change  may  be  deter- 
mined at  once  by  scratching  the  surface  of  a  crystal,  or  by 
crushing  it.  The  density  of  mercuric  iodide  in  the  state  of 
vapour  is  15630;  it  is  the  heaviest  of  gaseous  bodies.  Mer- 
curic iodide  is  slightly  soluble  in  water,  but  requires  more 
than  6000  times  its  weight  of  water  to  dissolve  it.  It  is  much 
more  soluble  in  alcohol  and  in  acids,  particularly  with  the 
assistance  of  heat.  Mercuric  iodide  is  very  soluble  in  iodide 
of  potassium ;  it  is  also  dissolved  by  a  solution  of  mercuric 
chloride,  especially  when  hot.  Hence,  when  a  few  drops  of 
iodide  of  potassium  solution  are  added  to  a  solution  of  corro- 
sive sublimate,  a  precipitate  is  formed,  which  redissolves  on 
agitating  the  liquid ;  a  somewhat  larger  quantity  of  iodide  of 
potassium  renders  the  precipitate  permanent ;  and  a  still 
further  addition  causes  it  to  disappear  entirely. 

When  treated  with  sulphuretted  hydrogen  water,  mercuric 
iodide  forms  the  compound  Hgl .  2HgS,  which  is  yeUow. 
Mcrcmic  iodide  unites  with  other  iodides,  and  forms  a  class 
of  salts  as  extensive  as  the  compounds  of  chloride  of  mercury. 
They  have  been  studied  by  M.  P.  BouUay.*     Mercuric  iodide 

*  Ann.  Ch.  Plijs.  [2],  xxxiv.  337. 


MERCURIC    IODIDE.  317 

also  combines  with  chlorides ;  it  is  dissolved  by  a  hot  solution 
of  mercuric  chloride,  and  two  compounds  have  been  obtained 
on  the  cooling  of  the  solution,  viz.,  a  yellow  powder,  Hgl .  HgCl, 
and  white  dendritic  crystals,  HgI.2HgCl. 

Mercuric  iodide  treated  with  very  strong  aqueous  ammonia 

forms  the  compound  NHgHg .  I ;  with  somewhat  less  concen- 
trated ammonia  it  yields  white  needles   of  the   compoimd 

NHg.SHgl  or  NHgHgl  +  Hgl,  and  a  red-brown  powder  con- 
sisting of  iodide  of  tetramercurammonium  with  2  eq.  water 
NHg4lH-2HO.  The  formation  of  this  last  compound  is 
represented  by  the  equation : 

4HgI  +  4NH3  +  2HO  =  NHgJ .  2H0  +  SNHJ. 

Iodide  of  tetramercurammonium  is  also  formed  by  passing 
ammoniacal  gas  over  mercuric  oxy-iodide : 

Hgl .  3HgO  +  NH3  =  NHgJ  .  2H0  +  HO  ; 

by  digesting  the  chloride  of  tetramercurammonium  in  aqueous 
iodide  of  potassium  (Rammelsberg) ;  and  by  adding  ammonia 
to  a  solution  of  iodide  of  mercury  and  potassium  mixed  with 
caustic  potash  (Nessler  *) : 

4(HgI .  KI)  +  NH3  +  3K0  =  NHg^I .  2H0  +  7KI  +  HO. 

This  last  reaction  affords  an  extremely  delicate  test  for  am- 
monia. A  solution  of  iodide  of  mercury  and  potassium  is 
prepared  by  adding  iodide  of  potassium  to  a  solution  of 
corrosive  sublimate,  till  a  portion  only  of  the  resulting  red 
precipitate  is  redissolved,  then  filtering,  and  mixing  the 
filtrate  with  caustic  potash.  The  liquid  thus  obtained  pro- 
duces a  brown  precipitate  with  a  very  small  quantity  of 
ammonia,  either  free  or  in  the  form  of  an  ammoniacal  salt. 
The  precipitate  is  soluble  in  excess  of  iodide  of  potassium 
(Nessler). 

*  Cheni.  Gaz.  1856,  445.  463. 
z  2 


318  MERCURY. 

Mercuroso-merciiric  iodide,  Hg^Ig  or  Hg2l .  2HgI. — This 
compound  is  obtained  by  precipitating  a  solution  of  mercurous 
nitrate  with  hydriodic  acid  or  iodide  of  potassium,  and  col- 
lecting the  precipitate  on  a  filter  after  the  green  colour  has 
changed  to  yellow ;  or  by  dissoMng  in  aqueous  iodide  of 
potassium  half  as  much  iodine  as  it  already  contains,  and 
adding  the  solution  to  a  solution  of  mercurous  nitrate.  It  is 
a  yellow  powder,  which  turns  red  when  heated. 

Cyanide  of  mercury,  HgCy,  126  or  1575.  —  This  salt  is 
most  easily  obtained  by  saturating  hydrocyanic  acid  Avith  red 
oxide  of  mercury.  To  prepare  the  hydrocyanic  acid  required, 
the  process  of  Winkler  may  be  followed.  Fifteen  parts  of 
ferrocyanide  of  potassium  are  distilled  with  13  parts  of  oil 
of  vitriol  diluted  with  100  parts  of  water,  and  the  distillation 
continued  by  a  moderate  heat  nearly  to  dryness.  The  vapour 
should  be  made  to  pass  through  a  Liebig's  condensing  tube, 
and  be  afterwards  received  in  a  flask  containing  30  parts  of 
water.  A  portion  of  the  condensed  hydrocyanic  acid  is  put 
aside,  and  the  remainder  mixed  with  16  parts  of  oxide  of  mer- 
cury in  fine  powder,  and  well  agitated  till  the  odour  of  hydro- 
cyanic acid  is  no  longer  perceptible.  The  solution  is  drawn 
off  from  the  undissolved  oxide  of  mercury,  and  the  reserved 
portion  of  hydrocyanic  acid  mixed  with  it.  The  last  addition 
is  necessary  to  saturate  a  portion  of  oxide  of  mercury,  which 
cyanide  of  mercury  dissolves  in  excess.  This  operation  yields 
12  parts  of  the  salt  in  question. 

Cyanide  of  mercury  may  also  be  obtained  by  boiling  1  pt. 
of  ferrocyanide  of  potassium  for  ten  minutes  with  2  pts.  of 
neutral  mercuric  sulphate  and  8  pts.  of  water,  filtering  the 
liquid,  and  leaving  it  to  crystallise  by  cooling.  The  reaction 
may  be  represented  by  the  equation : 

K2FeCy3  +  3HgO  =  3HgCy  +  2K0  +  FeO. 

A  third  method  of  preparing  tliis  compound  is  to  heat  the  red 
oxide  of  mercury  with  about  an  equal  weight  of  pure  and 


CYANIDE    OP    MERCURY.  319 

finely  pounded  Prussian  blue,  and  a  large  quantity  of  water, 
stirring  the  mixture  frequently;  then  boil  the  filtrate  with 
oxide  of  mercury  to  throw  down  the  last  portions  of  iron;  and 
neutralise  the  excess  of  mercuric  oxide  in  the  liquid  with 
hydrocyanic  acid. 

Cyanide  of  mercury  crystallises  in  square  prisms  which  are 
anhydrous,  and  resembles  chloride  of  mercury  in  its  solubility 
and  poisonous  qualities.  The  red  oxide  of  mercury,  even 
when  dry,  absorbs  hydrocyanic  acid,  with  formation  of  water 
and  evolution  of  heat.  The  affinity  of  mercury  for  cyanogen 
appears  to  be  particularly  intense,  oxide  of  mercury  decom- 
posing all  the  cyanides,  even  cyanide  of  potassium,  and  libe- 
rating potash.  Cyanide  of  mercury  is  consequently  not 
precipitated  by  potash.  Nor  is  it  decomposed  by  any  acid, 
with  the  exception  of  hydrochloric,  hydriodic,  and  hydrosul- 
phuric  acids.  By  a  heat  approaching  to  redness,  cyanide  of 
mercury  is  decomposed,  and  resolved  into  mercury  and 
cyanogen  gas.  When  exposed  in  the  moist  state  to  the 
action  of  chlorine  in  a  dark  place,  it  is  converted  into  mer- 
curic chloride  and  gaseous  chloride  of  cyanogen : 

HgCy  -i-  3C1  =  HgCl  +  CyCl. 

But  in  strong  sunshine,  a  difierent  action  takes  place,  attended 
with  considerable  rise  of  temperature,  and  yielding  sal-am- 
moniac, mercuric  chloride,  a  pecidiar  yellow  oil,  a  small  quan- 
tity of  gaseous  chloride  of  cyanogen,  and  a  trace  of  carbonic 
acid  (Serullas).  When  hydrocyanic  acid  is  digested  upon 
mercurous  oxide,  the  mercuric  cyanide  dissolves,  and  metallic 
mercury  is  liberated. 

Oxy cyanide  of  mercury ,  HgCy .  HgO,  is  produced  as  a  white 
powder  intermixed  with  the  red  oxide,  when  hydrocyanic  acid 
of  considerable  strength  (10  or  20  per  cent.)  is  agitated  with 
red  oxide  of  mercury  in  large  excess.  It  is  sparingly  soluble 
in  cold  water,  but  may  be  dissolved  out  by  hot  water,  and 
crystallises   on   cooling  in  transparent,   four-sided,   acicular 

z  3 


320  *  MERCURY. 

prisms.     When  heated  gently,  it  blackens  slightly,  and  then 
explodes  (Johnston).* 

Cyanide  of  mercury,  digested  upon  red  oxide  of  mercury, 
dissolves  a  large  quantity  of  it,  and  forms,  according  to  Kuhn, 
a  tribasic  cyanide  of  mercury ,  HgCy .  3HgO,  which  is  more 
soluble  in  water  than  the  neutral  cyanide,  and  crystallises  with 
less  facility  in  small  acicular  crystals. 

Cyanide  of  mercury  and  potassium ,  KyCy .  HgCy,  is  formed 
on  dissolving  cyanide  of  mercury  in  a  solution  of  cyanide  of 
potassium,  and  crystallises  in  regular  octohedrons.  Cyanide 
of  mercury  also  forms  crystallisable  double  salts  with  other 
cyanides,  such  as  the  cyanides  of  sodium,  barium,  calcium, 
magnesium,  &c.  It  also  combines  with  chlorides,  bromides, 
iodides,  and  with  several  oxi-salts,  such  as  cliromate  and 
formiate  of  potash,  with  which  it  forms  the  compounds 
2(K0  .  CrOg)  4-  HgCy  and  C2HKO,  .  IlgCy. 

Mercuric  sulphate,  HgO  .  SO3;  148  or  1850. — This  salt  is 
formed  by  boiling  5  parts  of  sulphuric  acid  upon  4  parts  of 
mercury,  till  the  metal  is  converted  into  a  dry  saline  mass. 
Mercuric  sulphate  is  a  white  crystalline  salt,  neutral  in  com- 
position, but,  like  most  of  the  neutral  salts  of  mercury,  cannot 
exist  in  solution.  Water  decomposes  it,  forming  a  dense 
yellow  subsulphate,  and  a  solution  of  an  acid  sulphate.  This 
subsulphate  is  known  as  turbith  mineral^  a  name  applied  to  it 
by  the  older  chemists,  because  it  was  supposed  to  produce 
effects  in  medicine  analogous  to  those  of  a  root  formerly 
employed,  and  known  as  convolvulus  turpcthura.  The  com- 
position of  turbith  mineral  is  3HgO .  SO3  or  HgO .  SO3  +  2HgO 
(Kane).  Solution  of  ammonia  converts  both  the  neutral  sul- 
phate and  turbith  mineral  into  a  hea^y  powder,  which  Kane 
names  ammonio-turbith,  and  finds  to  be  HgO.S03  +  Hg.NH2 
-|-2HgO.  It  is,  therefore,  analogous  in  composition  to  the 
yellow  powder  produced  by  the  decomposition  of  white  pre- 

*  PhU.  Trans.  1839,  p.  113. 


MERCURIC    SELENITES.  321 

cipitate^  and  may  be  regarded  as  a  sulphate  of  tetramercuram- 
monium  with  2  eq.  water :  NHg^  .  SO4  +  2H0. 

Mercuric  sulphites. — The  neutral  sulphite,  HgO  .  SO2,  may 
be  formed  by  precipitating  the  nitrate,  HgO  .  NO5,  with  an 
alkaline  sulphate ;  but  it  is  very  unstable,  and  resolves  itself 
spontaneously  into  mercuric  sulphate  and  metallic  mercury. 
The  basic  sulphite^  2HgO .  SO2,  is  obtained  by  precipitating 
a  solution  of  the  basic  nitrate,  2HgO  .  NO5,  with  an  alkaline 
sulphite.  It  is  a  white,  heavy  powder,  insoluble  in  water,  and 
changing,  when  slightly  heated,  into  mercurous  sulphate; 
2HgO  .  S02=Hg20.  SO3.  Iodide  of  potassium  converts  it 
into  red  mercuric  iodide  (Pean  de  St.  Gilles).*  A  bisulphite, 
HgO  .  2SO2  4-  HO,  is  obtained  as  a  white  crystalline  powder 
by  pouring  a  saturated  solution  of  bisulphite  of  soda  on  solid 
mercuric  chloride.  It  dissolves  readily  in  water,  and  is  de- 
composed by  heat,  whether  in  solution  or  in  the  solid  state, 
with  separation  of  metallic  mercury  (Wicke).t  By  treating 
mercuric  chloride  with  a  solution  of  neutral  sulphite  of  potash, 
a  double  salt,  HgO  .  SO2  +  HO,  is  obtained  in  small  needle- 
shaped  crystals,  whose  solution  is  neutral  to  test-paper. 
Similar  salts  are  formed  with  the  neutral  sulphites  of  soda 
and  ammonia.  By  treating  mercuric  chloride  in  excess  with 
neutral  sulphiteof  soda,  thesalt,2  (HgO.  SOg)  -f  NaO.  SOg  +  HO, 
is  obtained,  which  is  alkaline  to  test-paper.  The  solutions  of 
these  double  sulphites  are  precipitated  by  hydrosulphuric  acid 
and  soluble  sulphides,  but  not  by  alkalies.  (Pean  de  St. 
GiUes.) 

Mercuric  seleniate. — A  hot  aqueous  solution  of  selenic  acid 
forms  with  mercuric  oxide  prepared  by  precipitation,  a  soluble 
neutral  seleniate,  HgO  .  SeOg  +  HO,  and  a  red  insoluble  basic 
salt,  containing  2(3HgO  .  Se03)  +  H0  (Korner).t 

Mercuric  selenite. — Mercuric  oxide  forms   with   aqueous 

*  Ann.  Ch.  Phys.  [3],  xxxvi.  80.  f  Ann.  Ch.  Pharm.  xcv.  176. 

%  Pogg.  Ann.  Ixxxix.  146. 

z  4 


323  MERCURY. 

selenious  acid^  according  to  Berzelius,  an  insoluble  neutral 
and  a  soluble  acid  selenite ;  according  to  Kohler,  on  the  other 
hand,  selenious  acid  does  not  form  any  soluble  salt  with  mer- 
curic oxide,  but  only  a  pale  yellow  amorphous  salt,  containing 
7Hg0.4SeOj. 

Nitrates  of  the  red  oxide  of  mercury ,  Mercuric  nitrates. — 
The  neutral  nitrate  cannot  be  crystallised,  but  it  is  formed  in 
solution  when  chloride  of  mercury  is  precipitated  by  nitrate 
of  silver.  When  red  oxide  of  mercury  is  dissolved  in  nitric 
acid,  or  when  the  metal  is  dissolved  in  the  same  acid  with 
ebullition,  till  a  drop  of  the  solution  no  longer  occasions  a 
precipitate  in  water  containing  a  soluble  chloride,  a  subnitrate 
is  formed,  crystallising  in  small  prisms,  which  are  deliquescent 
in  damp  air.  Its  composition  is  expressed  by  the  formula 
2HgO  .NOg-f  2H0.  It  is  the  only  crystallisable  nitrate  of 
this  oxide.  Decomposed  by  water,  this  salt  yields  a  yellow 
subnitrate,  which,  after  washing  with  warm  but  not  boiling 
water,  is  3HgO  .  NO5  +  HO.  When  the  subnitrate  is  pre- 
pared by  boiling  water,  it  has  a  red  colour,  and  probably 
consists  of  6HgO  .  NO5  (Kane). 

Nitrate  of  mercury  yields  several  compounds  when  treated 
with  ammonia.  («.)  When  a  dilute  and  not  very  acid  solu- 
tion of  that  salt  is  treated  in  the  cold,  witli  weak  solution  of 
ammonia  not  added  in  excess,  a  pure  milk-Avliitc  precipitate 
appears,  which  is  not  granular,  and  remains  suspended  in  the 
liquid  for  a  considerable  time.  It  was  analysed  by  C.  G. 
Mitscherlich,  and  to  distinguish  it  from  some  other  salts  con- 
taining the  same  constituents,  may  be  called  Mitscherlich^ s 
ammonia-subnitrate.  It  contains  2HgO  .  IS  O5  +  HgNHg. 
[b.)  The  preceding  compound  is  altered  in  its  appearance  by 
boiling  water,  and  becomes  much  heavier  and  more  granular, 
forming  Soubeiraji's  ammonia-subnitrate,  the  composition  of 
which  is  found  by  Kane  to  be  HgO  .  NO5  -f  Hg .  NH2  +  2HgO, 
or  it  resembles  in  constitution  the  bodies  already  described 
containing  chlorine  and  sulphuric  acid.     This  compound  is 


MERCURIC    NITRATES.  323 

also  formed  by  decomposing  a  dilute  solution  of  mercuric 
nitrate  with  a  slight  excess  of  ammonia  (Soubeiran).  (c.)  A 
third  compound,  the  yellow  crysialline  ammonia-subnitrate, 
was  obtained  by  C.  G.  Mitscherlich  by  boiling  the  ammonia 
subnitrate  («)  with  excess  of  ammonia,  and  adding  nitrate  of 
ammonia,  by  which  a  portion  of  the  powder  is  dissolved ;  the 
solution,  as  it  cools  and  loses  ammonia,  yields  small  crystalline 
plates  of  a  pale  yellow  colour.  The  constituents  of  this  salt 
are  2HgO  .  NO5  and  NH3.  Kane  doubles  its  equivalent,  and 
represents  it  as  a  compound  of  Soubeiran^s  salt  with  nitrate 
of  ammonia,  as  it  appears  to  be  produced  by  the  solution  of 
the  former  salt  in  the  latter,  (HgO .  NO5  +  Hg  .NH2  +  HgO)  + 
NH4O  .  NO5.  [d.)  Soubeiran's  ammonia  subnitrate  {a)  is 
dissolved  in  considerable  quantity,  when  boiled  in  a  strong 
solution  of  nitrate  of  ammonia,  and  the  solution  deposits,  on 
cooling,  small  but  very  brilliant  needles,  which  were  observed 
and  analysed  by  Kane.  This  salt,  which  may  be  called  Kane's 
ammonia  subnitrate,  is  decomposed  by  water,  nitrate  of  am- 
monia dissolving,  and  Soubeiran^s  subsalt  being  left  undis- 
solved. It  contains  the  elements  of  3(NH40 .  NO5)  and 
4HgO.  Kane  believes  that  it  is  most  likely  to  contain 
Soubeiran^s  subnitrate  ready  formed,  which  leaves  two 
atoms  of  nitrate  of  ammonia  and  two  atoms  of  water  to  be 
otherwise  disposed  of.* 

These  ammonia-nitrates,  like  the  corresponding  chlorides 
and  sulphates,  may  be  regarded  as  nitrates  of  mercuram- 
moniums,  containing  one  or  more  atoms  of  mercury  in  place 
of  hydrogen.    Thus,  Mitscherlich' s  ammonia-subnitrate  [a)  is 

NHHgg.NOg  +  HO  =  nitrate  of  trimercurammonium  with 
1  eq.  water;  Soubeiran's  salt  {b)  is  NHg^ .  N06  +  2HO  = 
nitrate  of  tetramercurammonium  with  2  eq.  water;  the  crystal- 
line salt  (c)  is  NH2Hg2  .  NOg  +  HO  =  nitrate  of  bimercur- 
ammonium  with  1  eq.  water ;  and  [d)   is  a  compound  of  [b) 

*  Trans,  of  the  Royal  Irish  Academy,  toI.  xix.  pt.  i. ;  or,  Ann.  Ch.  Phys. 
[2],  Ixxii.  225. 


324  MERCURY. 

with  nitrate  of  ammonia  and  water  =  2(NH4.N06)  +  2H0  + 
(NHg^  .  NOg  +  2H0) . 

Nitrate  of  mercury  forms  an  insoluble  compound  with 
sulphide  of  mercury,  IlgO .  NOg  +  SHgS,  resembling  the 
compounds  of  the  sulphate  and  chloride  with  sulphide  of 
mercury.  It  also  forms  double  salts  with  iodide  and  cyanide 
of  mercury. 

Alloys  of  mercury  or  amalgams. — Mercury  combines  with  a 
great  number  of  metals,  forming  compounds  called  amalgams , 
which  are  liquid  or  solid  according  as  the  mercury  or  the 
other  metal  predominates.  A  very  small  quantity  of  a  foreign 
metal  suffices  to  impair  the  fluidity  of  mercury  in  a  very  great 
degree.  All  amalgams  are  decomposed  by  heat,  the  mercury 
volatilising  and  the  other  metal  remaining. 

The  union  of  mercury  with  potassium  and  sodium  is 
attended  with  considerable  disengagement  of  heat ;  the  re- 
sulting amalgams  are  of  a  pasty  consistence,  and  decompose 
water.  The  amalgams  of  tin  and  lead,  when  heated  till  they 
are  quite  liquid,  and  then  left  to  cool  slowly,  yield  solid  crys- 
talline amalgams  of  definite  constitution.  An  amalgam  of 
silver,  HgjAg,  is  found  native  in  the  form  of  regular  dodeca- 
hedrons. 

An  amalgam  of  tin  is  used  for  silvering  glass.  For  this 
purpose  a  sheet  of  tinfoil  is  laid  on  a  horizontal  table,  and 
mercury  poured  over  the  whole  surface,  so  as  to  form  a  layer 
about  l-5th  or  l-6th  of  an  inch  thick.  The  plate  of  glass 
is  then  slid  along  the  surface  in  such  a  manner  as  to  cut  this 
layer  in  halves  horizontally,  which  prevents  the  introduction 
of  air-bubbles.  The  glass  is  then  loaded  with  weights,  so  as 
to  press  out  the  excess  of  mercury ;  and  after  a  few  days,  the 
surface  is  found  to  be  covered  with  a  closely-adhering  layer 
of  an  amalgam  containing  about  5  parts  of  tin  to  1  of 
mercury. 

Mercury  combines  very  readily  with  bismuth.  An  amal- 
gam obtained  by  heating  a  mixture  of  497  pai'ts  of  bismuth. 


SEPARATION    OP    MERCURY.  325 

310  lead,  177  tin,  and  100  mercury,  is  very  well  adapted  for 
injecting  anatomical  preparations  :  it  is  solid  at  ordinary  tem- 
peratures, and  has  a  silvery  lustre,  melts  at  171*5  (Fah.),  and 
solidifies  at  140°.  An  amalgam  of  lead  and  tin,  sometimes 
also  containing  bismuth,  is  used  for  covering  the  cushions  of 
electrical  machines. 


ESTIMATION    OF    MERCURY,  AND    METHODS    OF    SEPARATING    IT  «* 

FROM    THE    PRECEDING    METALS. 

Mercury  is  generally  estimated  in  the  metallic  state ;  some- 
times, however,  as  sulphide,   HgS,  or  as  dichloride,  Hg2Cl. 
To  separate  it  from  its  compounds  in  the  metallic  state,  it 
may  be  distilled  with   quicklime,    in  a  tube  of  hard  glass 
sealed  at  one  end.     Into  this  tube  is  introduced,  first  a  layer 
of  carbonate  of  lime,  about  an  inch  long ;  then  the  mixture 
of  the  substance  with  quicklime;  lastly,  a  layer  of  quick- 
lime about  two  inches  long,  and  a  plug  of  asbestos  to  keep 
the  lime  in  its  place.    The  open  end  of  the  tube  is  next  drawn 
out  into  a  narrow  neck,  and  bent  at  an  obtuse  angle.     The 
tube  is  laid  in  a  combustion-furnace,  the  same  as  that  which 
is  used  for  organic  analysis  (I,  373),  the  neck  being  turned 
downwards  and  made  to  pass  into  a  narrow-mouthed  bottle 
containing  water,  so  as  to  terminate  just  above  the  surface  of 
the  water.     The  tube  is  then  gradually  heated  by  laying 
pieces  of  red-hot  charcoal  round  it,  beginning  at  the  part 
near  the  neck,  containing  the  pure  quicklime.      This  portion 
having  been  brought  to  a  full  red  heat,  the  heat  is  carefully 
extended  towards  the  middle  part,  to  decompose  the  com- 
pound and  volatilise  the  mercury :  any  portion  of  the  com- 
pound that  may  volatilise  undecomposed,  will  be  decomposed 
in  passing  over  the  red-hot  lime  at  the  end.    Lastly,  the  back 
part  of  the  tube  containing  the  carbonate  is  heated,  so  as  to 
evolve  carbonic  acid  gas  and  sweep  out  all  the  mercury  vapour 
contained  in  the  tube.     The  quantity  of  carbonic  acid  thus 


326  MERCURY. 

evolved  may  be  increased  by  mixing  the  carbonate  of  lime 
with  bicarbonate  of  soda.  The  mercury  condenses  under  the 
water  in  the  bottle,  which  must  be  kept  cold.  The  water  is 
poured  off  as  completely  as  possible ;  the  mercury  transferred 
to  a  weighed  porcelain  crucible ;  the  greater  part  of  the  water 
which  still  adheres  to  it  removed  by  means  of  blotting-paper ; 
the  drying  completed  over  sulphuric  acid ;  and  the  mercury 
finally  weighed. 

Mercury  may  also  be  precipitated  from  its  solutions  in  the 
metallic  state  by  protochloride  of  tin,  or  by  phosphorous  acid ; 
the  solution  then  decanted ;  the  mercury  washed  with  water ; 
and  dried  in  the  manner  just  described. 

Mercury  is  also  frequently  precipitated  from  its  solutions, 
as  a  sulphide,  by  hydrosulphuric  acid.  In  that  case,  if  the 
precipitate  consists  of  the  pure  protosulphide,  HgS,  as  when 
it  is  thrown  down  from  a  solution  of  corrosive  sublimate,  the 
precipitate  may  be  simply  collected  on  a  weighed  filter, 
washed,  dried  over  the  water-bath,  weighed,  and  the  quantity 
of  mercury  thence  determined.  But  if,  as  is  generally  the 
case,  the  precipitate  also  contains  free  sulphur,  as  when  it  is 
thrown  down  from  a  solution  containing  a  ferric  salt,  or  a 
considerable  excess  of  nitric  acid, — or  if  it  be  precipitated  in 
conjunction  with  the  sulphides  of  other  metals,  then  the  mer- 
cury must  be  separated  from  it  by  distillation  with  lime,  as 
above  described.  Or  again,  the  mixture  of  sulphides  may  be 
converted  into  chlorides  by  gentle  heating  in  a  stream  of 
chlorine  gas,  the  volatile  chloride  of  mercury  passed  into 
water,  and  the  mercury  precipitated  from  the  solution  by 
protochloride  of  tin. 

The  precipitation  of  mercury  in  the  form  of  dichloride  is 
best  effected  by  means  of  hydrochloric  acid  and  formiate  of 
potash  or  soda.  If  the  mercury  is  contained  in  an  alloy,  the 
alloy  must  be  dissolved  in  aqua-regia ;  if  it  is  contained  in 
solution  in  the  form  of  mercuric  nitrate,  hydrochloric  acid 
must  be  added,  the  solution,  in  either  case,  nearly  neutralised 


SEPARATION    OF    MERCURY.  327 

^vith  potash,  formiate  of  potash  or  soda  thea  added,  and  the 
whole  exposed  for  some  days  to  a  temperature  between  140° 
and  176°  F.  (at  the  boiling  heat,  the  mercury  would  be  re- 
duced to  the  metallic  state.)  The  dichloride  then  precipitates, 
and  must  be  collected  on  a  weighed  filter,  washed,  dried  at  a 
gentle  heat,  and  weighed. 

The  quantity  of  mercurous  oonide  present  in  a  solution  may 
also  be  determined  by  precipitation  with  hydrochloric  acid. 
The  solution  must,  however,  be  very  dilute,  and  be  kept  cool ; 
it  must  also  contain  but  a  very  small  quantity  of  free  nitric 
acid,  as  a  larger  quantity  would  convert  the  dichloride  of 
mercury  into  protochloride.  To  determine  the  proportions 
of  mercurous  and  mercuric  oxide,  when  they  exist  together  in 
solution,  the  mercurous  oxide  is  first  precipitated  with  hydro- 
chloric acid,  and  the  remaining  mercury  by  protocjiloride  of 
tin  or  hydrosulphuric  acid. 

Mercury  may  be  separated  from  all  other  metals,  except 
arsenic  and  antimony,  by  its  superior  volatility.  When  it 
exists  in  the  form  of  an  amalgam,  the  compound  is  simply 
heated,  and  the  quantity  of  mercury  determined  by  the  loss 
of  weight.  If  it  exists  as  an  oxide,  chloride,  &c.,  combined 
with  compounds  of  other  metals,  it  may  be  separated  by  dis- 
tillation with  quicklime,  as  above  described.  Its  separation 
from  the  alkalies  and  earths,  and  from  uranium,  manganese, 
nickel,  cobalt,  iron,  zinc,  and  chromium,  may  also  be  effected 
by  precipitation  with  hydrosulphuric  acid.  From  bismuth 
and  cadmium  it  may  be  separated  by  reduction  with  proto- 
chloride of  tin;  from  copper,  by  mixing  the  solution  with 
excess  of  cyanide  of  potassium,  and  passing  hydrosulphuric 
acid  through  the  liquid,  whereby  the  mercury  is  precipitated 
as  sulphide,  while  the  copper  remains  dissolved ;  from  lead, 
by  precipitating  that  metal  with  sulphuric  acid;  also  by 
treating  the  solution  with  excess  of  cyanide  of  potassium,  which 
precipitates  the  lead,  but  not  the  mercury.  From  arsenic, 
tin  and  antimony,  mercury  is  separated  by  the  solubility 
of  the  sulphides  of  those  metals  in  sulphide  of  ammonium. 


328  SILVER. 


SECTION  11. 

SILVER. 

Eq.  108,  or  1350;  Ag  [argentum). 

This  metal  is  found  iii  various  parts  of  the  world,  and  oc- 
curring often  in  the  metallic  state,  and  being  easily  melted, 
must  have  attrabted  the  attention  of  mankind  at  an  early 
period.  Before  the  discovery  of  America,  the  silver  mines  of 
Saxony  were  of  considerable  importance ;  but  the  silver  mines 
of  Mexico  and  Peru  far  exceed  in  value  the  whole  of  the 
European  and  Asiatic  mines,  the  former  having  furaished 
during  the  last  three  centuries,  according  to  Humboldt,  316 
millions  of  pounds  troy  of  pure  silver. 

A  considerable  quantity  of  silver  is  obtained  from  ores  of 
lead  by  cupellation,  as  described  under  that  metal.  From 
argentiferous  copper  ores  also  the  silver  is  exti'actcd  by  a  pro- 
cess called  liquation^  which  consists  in  fusing  the  coarse 
copper  (p.  93.)  with  three  times  its  weight  of  lead ;  a  mix- 
ture of  two  alloys  is  then  obtained,  the  more  fusible  of  which, 
containing  the  greater  part  of  the  lead  and  nearly  all  the 
silver,  is  separated  by  the  application  of  a  moderate  heat,  and 
yields  the  silver  by  cupellation. 

Native  silver,  which  is  in  the  form  of  threads  or  thin  leaves, 
is  separated  from  the  gangue  or  accompanying  rock,  by  amaU 
gamation,  a  process  which  is  also  followed  in  the  treatment  of 
the  most  frequent  ore  of  silver,  the  sulphide,  when  it  is  not 
accompanied  by  sulphide  of  lead.  At  Freiberg,  in  Saxony,  the 
sulphide  of  silver,  ground  to  powder,  is  roasted  in  a  reverbera- 
tory  furnace  with  10  per  cent,  of  chloride  of  sodium,  by  which 
the  silver  is  converted  into  chloride.  It  is  then  introduced  into 
barrels  (fig.  19.),  with  water,  iron,  and  a  quantity  of  metallic 


SILVER.  329 

mercury,  and  the  materials  kept  in  a  state  of  agitation  for 

eighteen  hours  by  the  revolution  of  the   barrels   on  their 

axes.      The   chloride   of   silver.  ^-     ,q 

'  iug.  ly. 

although   insoluble,  is   reduced 

to.  the  metallic  state  by  the  iron, 

and  chloride  of  iron  is  produced, 

while  the  silver  forms  a  fluid 

compound   with    the    mercury. 

By    adding    more    water,    and 

turning  the  barrels  more  slowly, 

the  fluid  amalgam  separates  and 

subsides.     It  is  drawn  off  and 

subjected  to  pressure  in  a  chamois  leather  bag,  the  mercury 

passing  through  the  leather^  while  a  soft  amalgam  of  silver 

remains  in  the  bag.     The  mercury  is  afterwards  separated 

from  this  amalgam  by  a  species  of  distillation,  per  descen- 

swTij  and  the  silver  remains. 

In  South  America,  where  fuel  is  scarce,  a  different  process 
is  adopted.  The  ore,  in  a  finely  divided  and  moist  condition, 
is  exposed  for  a  considerable  time  to  the  successive  action  of 
common  salt,  sulphate  of  copper  (obtained  by  roasting  copper 
pyrites),  and  mercury,  the  materials  being  spread  on  a  paved 
floor,  and  trodden  by  men  or  horses  to  effect  an  intimate  mix- 
ture ;  and  the  silver  amalgam  thus  obtained  is  separated  from 
the  exhausted  ore  by  washing  with  water.  In  this  process, 
the  chloride  of  sodium  and  sulphate  of  copper  form  sulphate 
of  soda  and  protochloride  of  copper.  The  latter  gives  up 
chlorine,  converting  part  of  the  silver  into  chloride,  and 
separates  the  sulphur,  provided  an  excess  of  chloride  of 
sodium  is  present  to  dissolve  the  dichloride  of  copper  as  it 
forms.  The  dichloride  of  copper  then  acts  upon  another 
portion  of  the  sulphide  of  silver,  forming  disulphide  of  copper 
and  chloride  of  silver:  Cu^Cl  +  AgSrrrCu^S  +  AgCl.  The 
chloride  of  silver  thus  produced,  dissolves  in  the  chloride  of 
sodium,   and  is  decomposed   by  the   mercury   subsequently 


330  SILVER. 

added,  yielding  calomel  and  metallic  silver.  This  process  is 
always  attended  with  considerable  loss  of  mercury,  which 
however  may  be  diminished  by  the  previous  addition  of  iron. 
Mr.  P.  Johnston  proposes  to  diminish  the  loss  of  mercury,  as 
soluble  chloride,  which  occurs  in  this  process,  by  using  an 
amalgam  of  zinc  and  mercury,  instead  of  pure  mercury. 

Silver  is  obtained  free  from  other  metals,  and  in  a  state  of 
purity,  for  chemical  and  other  purposes,  by  the  following 
processes :  —  1 .  The  metal  is  dissolved  in  pure  nitric  acid 
slightly  diluted,  and  precipitated  by  a  solution  of  chloride  of 
sodium,  the  salts  of  the  other  metals  present  remaining  in 
solution.  The  insoluble  chloride  of  silver,  thus  obtained,  is 
thoroughly  washed  upon  a  filter  with  hot  water  and  dried.  A 
quantity  of  carbonate  of  potash,  equal  to  twice  the  weight  of 
the  silver,  is  then  fused  in  a  crucible,  and  the  chloride  of 
silver  gradually  added  to  it,  whereupon  cldoridc  of  potassium 
is  formed,  and  carbonic  acid  and  oxygen  escape  with  effer- 
vescence. The  crucible  is  then  exposed  to  a  heat  sufficient  to 
fuse  the  reduced  silver,  which  subsides  to  the  bottom. — 2.  The 
mode  of  separating  silver  from  the  common  metals,  in  the 
ordinaiy  practice  of  assaying,  is,  like  many  mctallurgic  opera- 
tions, an  exceedingly  elegant  and  refined  process.  A  portion 
of  the  silver  alloy,  the  assay,  is  fused  with  several  times  its 
weight  of  pure  lead  (an  alloy  of  1  copper  and  15  silver  with 
96  lead,  for  instance)  upon  a  bone-earth  cupel,  which  is  sup- 
ported in  a  little  oven  or  muffle,  heated  by  a  proper  furnace. 
Air  being  allowed  access  to  the  assay,  the  lead  is  rapidly  oxi- 
dated, and  its  highly  fusible  oxide  imbibed,  as  it  is  produced, 
by  the  porous  cupel.  The  disposition  of  copper  and  other 
common  metals  to  oxidate  is  increased  by  the  presence  of  the 
lead;  and  their  oxides,  which  form  fusible  compounds  with 
oxide  of  lead,  are  removed  in  company  with  the  latter,  ^hen 
the  foreign  metal  is  almost  entirely  removed,  the  assay  is 
observed  to  become  rounder  and  more  brilliant,  and  the  last 
trace  of  fused  oxide  occasions  a  beautiful  play  of  prismatic 


SILVER.  331 

colours  upon  its  surface,  after  which  the  assay  becomes,  in  an 
instant,  much  whiter,  ov  flashes,  an  indication  that  the  cupel- 
lation  is  completed. 

Pure  silver  may  also  be  obtained  from  an  alloy  containing 
only  silver  and  copper,  by  precipitating  the  two  metals  with 
excess  of  carbonate  of  soda  with  the  aid  of  heat,  boiling  the 
precipitate  for  about  ten  minutes  with  a  solution  of  grape- 
sugar,  whereby  the  copper  is  reduced  to  the  state  of  red 
oxide,  and  the  silver  to  the  metallic  state,  and  treating  the 
moist  precipitate  with  a  hot  solution  of  carbonate  of  ammonia: 
the  copper  then  dissolves,  and  pure  silver  remains. 

Pure  silver  is  the  whitest  of  the  metals,  and  susceptible 
of  the  highest  polish ;  when  granulated  by  being  poured 
from  a  height  of  a  few  feet  into  water,  its  surface  is  rough, 
but  its  aspect  peculiarly  beautiful.  It  crystallises  in  cubes 
and  regular  octohedrons,  both  from  a  state  of  fusion  and 
by  precipitation  from  solution.  Silver  is  in  the  highest 
degree  ductile  and  malleable;  its  density  varies  between 
10-474  and  10*542;  it  fuses  at  1873^  When  in  the  liquid 
state,  it  is  capable  of  absorbing  oxygen  gas  from  the  air, 
which  is  discharged  again  in  the  solidification  of  the  metal, 
and  gives  rise  to  a  sort  of  vegetation  upon  its  surface,  or 
even  occasions  the  projection  of  small  portions  of  the  silver 
to  a  distance,  an  accident  which  is  known  in  assaying  as  the 
spitting  of  the  metal,  Gay-Lussac  observed,  that  when  a 
little  nitre  was  thrown  upon  the  surface  of  melted  silver  in  a 
crucible,  and  the  whole  kept  in  a  state  of  fusion  for  half  an 
hour,  a  very  considerable  absorption  of  oxygen  took  place. 
"When  the  crucible  was  removed  from  the  fire  and  quickly 
placed  under  a  bell-jar  filled  with  water,  which  can  be  done 
without  danger,  the  silver  discharged  a  quantity  of  oxygen 
equal  to  20  times  its  volume.  This  property  is  possessed  only 
by  pure  silver,  and  does  not  appear  at  all  in  silver  con- 
taining 1  or  2  per  cent,  of  copper.  As  oxide  of  silver  is  re- 
duced by  a  red  heat,  the  absorption  of  the  oxygen  by  the 

VOL.  II.  A  A 


332  SILVER. 

fluid  metal  must  be  a  phenomenon  of  a  different  nature  from 
simple  oxidation. 

Silver  does  not  combine  witli  the  oxygen  of  the  air  at  the 
usual  temperature,  nor  even  when  heated ;  the  tarnishing  of 
polished  silver  in  air  is  occasioned  by  the  formation  of  sul- 
phide of  silver.  Silver  does  not  dissolve  in  any  hydrated  acid, 
by  substitution  for  hydrogen,  but  on  the  contrary  is  dis- 
placed from  solution  in  an  acid  by  hydrogen,  and  precipi- 
tated in  the  metallic  state.  This  metal  is  also  precipitated  by 
mercury  and  by  all  the  more  oxidable  metals.  Its  salts  are 
reduced  at  the  usual  temperature  by  sulphate  of  iron,  the 
protoxide  in  which  is  converted  into  sesquioxidc.  But  if  the 
ferric  sulphate  is  boiled  upon  the  precipitated  silver,  the 
latter  is  dissolved  again,  and  oxide  of  silver  and  protoxide  of 
iron  reproduced.  Silver,  however,  is  oxidated  when  fused  or 
heated  strongly  in  contact  with  substances  for  which  oxide  of 
silver  has  a  great  affinity,  as  with  a  siliceous  glass,  and  stains 
the  glass  yellow.  It  is  oxidated  by  concentrated  sulphuric 
acid,  with  evolution  of  sulphurous  acid.  Silver  is  readily 
dissolved  by  nitric  acid,  at  a  gentle  heat,  and  with  much 
violence,  at  a  high  temperature,  nitrate  of  silver  being  formed, 
and  nitric  oxide  escaping.  Silver  combines  in  three  propor- 
tions with  oxygen,  forming  a  suboxide,  AgjO,  a  protoxide 
AgO,  and  a  peroxide,  AgOg. 

Suboxide  of  silver,  K^j^- — I*^^e  protoxide  of  silver  is  com- 
pletely reduced  to  the  state  of  metal  by  hydrogen  gas,  at 
212° ;  but  the  oxide  contained  in  citrate  of  silver  loses  only 
half  its  oxygen  under  the  same  circumstances,  the  suboxide 
being  formed  and  remaining  in  combination  with  one  half  of 
the  citric  acid  of  the  former  salt.  The  aqueous  solution  of 
the  suboxide  salt  is  dark  brown,  and  the  suboxide  is  precipi- 
tated black  from  it  by  potash.  When  the  solutioYi  of  the 
subsalt  is  heated,  it  becomes  colourless,  and  metallic  silver 
appears  in  it.  The  salt  dissolves  with  a  brown  colour  in 
ammonia.     Several  other  salts  of  silver,  containing  organic 


PROTOXIDE    OP    SILVER.  333 

acids^  comport  themselves  in  the  same  way  as  the  citrate, 
when  heated  in  hydrogen.*  A  solution  of  protoxide  of  silver 
in  ammonia  deposits  on  exposure  to  the  air,  a  grey  suboxide, 
containing  108  parts  of  silver  to  5*4  parts  oxygen.  When 
heated,  it  gives  off  oxygen  and  leaves  metallic  silver  (Fara- 
day).f 

Protoxide  of  silver,  AgO,  116  or  1450. — This  oxide  is 
thrown  down,  when  potash  or  lime-water  is  added  to  a  solution 
of  nitrate  of  silver,  as  a  brown  powder,  which  becomes  of  a 
darker  colour  when  dried.  The  powder  was  found  to  be 
anhydrous  by  Gay-Lussac  and  Thenard  j  its  density  is  7*143, 
according  to  J.  Herapath ;  7'250,  according  to  P.  Boullay ; 
8*2558,  according  to  Karsten.  Oxide  of  silver  is  decomposed 
by  light,  or  at  a  red  heat,  into  oxygen  gas  and  metallic  silver. 
Hydrogen  reduces  it  even  at  212°.  It  is  also  reduced  by  an 
aqueous  solution  of  phosphorous  acid.  When  recently  preci- 
pitated, it  is  decomposed  by  aqueous  sulphurous  acid,  yielding 
metallic  silver  and  sulphate  of  silver;  but  the  decomposition 
is  only  partial,  even  when  aided  by  heat.  When  immersed  in 
water,  it  is  reduced  by  zinc,  cadmium,  tin,  and  copper,  but  not 
by  iron  or  mercury.  In  an  aqueous  solution  of  hypochlorous 
acid,  it  is  converted  into  chloride  of  silver,  oxygen  being 
evolved  together  with  a  small  quantity  of  chlorine. 

Oxide  of  silver  is  a  powerful  base,  and  forms  salts,  several 
of  which  have  been  found  isomorphous  with  the  corresponding 
salts  of  soda.  Like  oxide  of  lead,  it  dissolves  to  a  small 
extent  in  pure  water  free  from  saline  matter,  and  the  solution 
has  an  alkaline  reaction.  Oxide  of  silver  is  not  dissolved  by 
solutions  of  the  hydrates  of  potash  and  soda.  Its  salts  are 
precipitated  black  by  hydrosulphuric  acid  and  alkaline  sul- 
phides. When  treated  with  hydrochloric  acid  or  a  soluble 
chloride,  they  yield  a  white  cm^dy  precipitate,  the  chloride  of 
silver,  which  soon  becomes  purple,  if  exposed,  while  moist,  to 

*  Ann.  Ch.  Pharm.  xxx.  1.  f  Ann.  Ch.  Pbys.  [2],  ix.  107. 

A  A  2 


33i  SILVER. 

the  direct  rays  of  the  sun.  This  precipitate  is  not  dissolved 
by  nitric  acid^  but  is  dissolved  by  ammonia  in  common  with 
most  of  the  insoluble  salts  of  silver.  This  precipitate  is 
visible,  according  to  Lassaigne,  even  in  solutions  containing 
only  1  part  of  silver  in  800,000  parts  of  liquid.  In  a  solution 
containing  1  part  of  silver  in  200,000  parts,  hydrochloric  acid 
or  common  salt  produces  a  slight  tm-bidity ;  with  1  part  of 
silver  in  400,000,  the  same  reagents  produce  a  scarcely  per- 
ceptible opalescence ;  and  if  the  proportion  of  liquid  amounts 
to  800,000  parts,  the  opalescence  does  not  show  itself  for  a 
quarter  of  an  hour.  Hydrobromic  acid  and  soluble  metallic 
bromides  J  added  to  solutions  of  silver  salts,  throw  down  all  the 
silver  in  the  form  of  yellowish  white  bromide,  insoluble  in 
nitric  acid,  and  sparingly  soluble  in  ammonia.  Hydriodic 
acid  and  soluble  iodides  form  a  pale  yellow  precipitate  of 
iodide  of  silver,  likewise  insoluble  in  nitric  acid,  and  still  less 
soluble  in  ammonia.  Hydrocyanic  acid  and  soluble  cyanides 
throw  down  a  white  precipitate  of  cyanide  of  silver,  easily 
soluble  in  ammonia,  insoluble  in  cold  dilute  nitric  acid,  but 
dissolved  by  strong  nitric  acid  at  a  boiling  heat,  with  evolu- 
tion of  nitric  oxide.  Ammonia  added  in  very  small  quantity 
to  perfectly  neutral  silver-salts,  produces  a  slight  brown  pre- 
cipitate of  oxide  of  silver,  easily  soluble  in  excess ;  but  if  the 
solution  contains  excess  of  acid,  ammonia  produces  no  preci- 
pitate. Potash  added  to  the  ammoniacal  solution  produces  a 
white  precipitate,  provided  the  excess  of  ammonia  be  but 
small.  The  fixed  alkalies  form,  in  neutral  or  acid  solutions  of 
silver-salts,  a  brown  precipitate  of  oxide  of  silver,  insoluble 
in  excess.  Alkaline  carbonates  precipitate  white  carbonate 
of  silver,  soluble  in  ammonia  and  carbonate  of  ammonia. 
Ordinary  tribasic  phosphate  of  soda  forms  a  yellow  precipi- 
tate; pyrophosphate  and  metaphosphate  of  soda  form  white 
precipitates.  Chromate  of  potash  forms  a  dark  crimson  pre- 
cipitate of  chromate  of  silver.  Alkaline  arsenites  form  a 
canary-yellow  precipitate  of  arsenite  of  silver.     Oxalic  acid 


PROTOXIDE    OF    SILVER.  335 

forms  a  white  pulverulent  precipitate  of  oxalate  of  silver. 
Silver  is  precipitated  from  its  solutions  in  the  metallic  state 
by  phosphorus,  phosphorous  acid,  phosphuretted  hydrogen,  and 
sulphurous  acid  (imperfectly) ;  by  various  metals,  viz.,  zinc, 
cadmium,  tin,  lead,  iron,  manganese,  copper,  mercury,  bis- 
muth, tellurium,  antimony,  and  arsenic ;  also  by  protoxide  of 
uranium,  hydrated  protoxide  of  manganese,  and  protoxide  of 
tin;  and  by  various  organic  substances  at  a  boiling  heat, 
e.  g.,  charcoal,  sugar,  aldehyde,  formic  acid,  tincture  or  infusion 
of  galls,  and  volatile  oils.  Many  organic  substances  added  to 
a  solution  of  nitrate  of  silver  mixed  with  excess  of  ammonia, 
throw  down  metallic  silver  in  the  form  of  a  beautiful  specular 
film  lining  the  sides  of  the  vessel.  This  eflPect  is  produced  by 
aldehyde,  saccharic  acid,  salicylous  acid,  pyromeconic  acid, 
and  various  essential  oils.  A  mixture  of  oil  of  cinnamon  and 
oil  of  cloves  is  found  to  produce  an  exceedingly  brilliant 
speculum,  and  has  indeed  been  used  for  silvering  mirrors  in 
place  of  the  ordinary  process  with  tin  and  mercury ;  it  is  par- 
ticularly adapted  for  silvering  curved  surfaces.  A  very  bright 
and  regular  specular  surface  is  also  produced  by  adding  a 
solution  of  milk-sugar  to  an  ammoniacal  solution  of  nitrate  of 
silver  mixed  with  caustic  potash  or  soda;  the  precipitation 
then  takes  place  without  the  application  of  heat  (Liebig)  .* 

Oxide  of  silver  combines  with  ammonia  and  forms  the  ful- 
minating ammoniuret  of  silver,  a  substance  of  a  dangerous 
character  from  the  violence  with  which  it  explodes.  The 
ammoniuret  may  be  formed  by  digesting  newly  precipitated 
oxide  of  silver  in  strong  ammonia,  or  more  readily  by  dis- 
solving nitrate  of  silver  in  ammonia,  and  precipitating  the 
liquor  by  potash  in  slight  excess.  If  this  substance  be  pressed 
by  a  hard  body,  while  still  moist,  it  explodes  with  unequalled 
violence ;  when  dry,  the  touch  of  a  feather  is_  often  sufficient 
to  cause  it  to  fulminate.     The  explosion  is  obviously  occa- 

*  Ann.  Ph.  Pharm.  xcviii.  132. 

A  A   3 


336  SILVER. 

sioned  by  the  reduction  of  the  silver  from  the  combination  of 
its  oxygen  with  the  hydrogen  of  the  ammonia,  and  the  evolu- 
tion of  nitrogen  gas. 

Sulphide  of  silver j  AgS,  124  or  1550. — Sulphur  and  silver 
may  be  combined  together  by  fusion ;  the  excess  of  sulphur 
escapes,,  and  at  a  high  temperature  the  sulphide  melts;  it 
forms^  on  coohng,  a  crystalline  mass.  This  compound  has  a 
lead-grey  colour  and  metallic  lustre.  It  is  so  soft  that  it  may 
be  cut  ^dth  a  knife,  and  is  malleable.  The  sulphide  of  silver 
is  also  rcmai'kable  for  conducting  electricity,  like  a  metal, 
when  warmed.  The  same  compound  occurs  in  nature,  some- 
times crystallised  in  octohedi'ons  with  secondary  faces.  This 
sulphide  is  particularly  interestmg  from  being  isomorphous 
with  the  subsulphide  of  copper,  AgS  with  CujS  (page  144). 
These  two  sulphides  replace  each  other  in  indeterminate  pro- 
portions in  several  double  sulphides  of  silver  and  other  metals, 
as  in  polybasite  and  fahl-ores,  the  composition  of  which  may 
be  expressed  by  the  following  formulae,  the  symbols  placed 
above  each  other  representing  constituents,  of  which  cither 
the  one  or  the  other  may  be  present : 

Polybasite     .     O^^^f +^^^3 

-p  ,,  /,ZnS^  SbSA  ,  o/.AgS    ,  SbSA 

Fahl-orcs    {^^^.^^  +AsS3)  +  H^Cu,S+AsS3)- 

Chloride  of  silver,  AgCl,  143*5  or  1793-75.  — This  salt 
contains  in  100  parts,  21*G9  parts  of  chlorine,  and  75-31 
parts  of  silver.  It  is  found  native  as  horn-silver ,  in  trans- 
lucent cubes  or  octohedrons  of  a  greyish-white  colour,  and 
specific  gravity  5-55.  The  same  compound  is  also  thrown 
down  as  a  white  precipitate,  at  first  very  bulky  and  curdy, 
when  hydrochloric  acid  or  a  soluble  chloride  is  added  to  any 
soluble  salt  of  silver,  except  the  hyposulphite.  It  is  wholly 
insoluble  in  water,  and  the  most  miimte  quantity  of  hydro- 
chloric acid  contained  in  water  may  be  detected  by  adding  to 


CHLORIDE    OF    SILVER.  337 

it  a  drop  of  a  solution  of  nitrate  of  silver  (p.  336.)  Hydro- 
cUoric  acid,  when  concentrated,  dissolves  chloride  of  silver, 
which  crystallises  from  it  in  octohedrons,  when  the  solution 
is  evaporated.  This  salt  dissolves  easily  in  solution  of  am- 
monia, and  crystallises  also  as  the  ammonia  evaporates.  When 
heated,  it  fuses  at  about  500°,  forming  a  transparent  yellowish 
liquid,  which  becomes,  after  cooling,  a  mass  that  may  be  cut 
with  a  knife,  and  has  considerable  resemblance  to  horn:  a 
property  to  which  it  was  indebted  for  the  name  of  horn-silver, 
applied  to  it  by  the  older  chemists.  It  is  not  volatile. 
Chloride  of  silver  is  not  affected  by  a  concentrated  solution 
of  potash.  It  is  easily  reduced  to  the  state  of  metal  by  zinc 
or  iron  with  water.  Chloride  of  silver  may  be  dissolved  out 
in  this  way  by  means  of  zinc  and  acidulated  water,  from  a 
porcelain  crucible  in  which  it  has  been  fused.  To  obtain 
pure  silver  by  this  mode  of  reduction,  it  is  necessary  to  use 
zinc  free  from  lead,  otherwise  that  metal,  not  being  dissolved 
by  the  sulphuric  acid,  remains  mixed  with  the  silver.  A 
better  mode  of  reduction  is  to  boil  the  chloride  of  silver  with 
an  equal  weight  of  starch-sugar  and  a  solution  of  one  part  of 
carbonate  of  soda  in  three  parts  of  water  (Bottger).  The 
chloride  and  other  salts  of  silver  acquire  a  dark  colour  when 
exposed  to  light ;  chlorine  escapes,  and  a  portion  of  the  salt 
appears  to  be  reduced  to  the  metallic  state,  as  the  blackened 
surface  conducts  electricity.  According  to  Wetzlar,  the  black 
substance  contains  an  inferior  chloride  of  silver,  and  is  not 
attacked  by  nitric  acid,  or  soluble  in  ammonia.  It  has  also 
been  supposed  that  the  blackening  is  due,  not  to  any  chemical 
decomposition,  but  merely  to  a  change  in  the  state  of  aggre- 
gation of  the  particles.  It  appears,  however,  from  some  recent 
experiments  by  Dr.  F.  Guthrie,  that  the  chloride  is  com- 
pletely decomposed  and  metallic  silver  separated,  even  in 
presence  of  free  nitric  acid.  Paper  charged  with  chloride  of 
silver  is  very  sensitive  to  the  impression  of  light,  and  is  the 
material  used  for  positive  photographs,  tlie  unaltered  chloride 

A  A  4 


338  SILVER. 

being  afterwards  dissolved  out  by  a  solution  of  hyposulphite 
of  soda. 

One  hundred  parts  of  chloride  of  silver  absorb  17'9  parts  of 
ammoniacal  gas,  forming  the  compound,  3NH3 .  2AgCl,  or 


N  H(NH4)2Ag|  ^^^^     ,pj^.g  compound  gives  off  its  ammonia 

in  the  air.  Chloride  of  silver  is  dissolved  by  concentrated 
and  boiling  solutions  of  the  chlorides  of  potassium,  sodium, 
and  ammonium,  and,  on  cooling,  a  double  salt  is  deposited  in 
crystals,  generally  cubes.  Chloride  of  silver  is  also  dissolved 
by  cyanide  of  potassium,  and  the  solution  yields  a  double  salt 
by  evaporation  (Liebig). 

Bromide  of  silver^  AgBr,  188  or  2350. —  This  salt  consists 
in  100  parts,  of  42*56  bromine  and  57*M'  silver.  It  is  found 
native  in  Mexico  and  in  Bretagne ;  sometimes  in  small 
amorphous  masses,  sometimes  in  greenish-yellow  octohedral 
crystals.  It  is  insoluble  in  water,  and  falls  as  a  precipitate 
which  is  white  at  first,  but  becomes  pale  yellow  when  col- 
lected. When  fused  and  cooled,  it  yields  a  mass  of  a  pure 
and  intense  yellow  colour.  It  has  most  of  the  properties  of 
chloride  of  silver,  but  dissolves  very  sparingly  in  ammonia. 

Iodide  of  silver,  Agl,  231-36  or  2929-5.— This  salt  con- 
tains in  100  parts,  53*87  of  iodine  and  16*13  of  silver.  It  is 
found  native,  sometimes  in  regular  hexagonal  prisms.  It  is 
insoluble  in  water,  like  the  chloride,  and  is  prepared  in  a 
similar  manner  by  precipitation,  but  is  distinguished  from 
that  salt  by  its  colour,  which  is  pale  yellow,  by  the  difficulty 
with  which  it  is  dissolved  in  ammonia,  ])eing  even  less  soluble 
than  the  bromide,  and  by  being  blackened  more  slowly  by  the 
action  of  light.  According  to  Martini,  2500  parts  of  am- 
monia, of  density  0-960,  are  required  to  dissolve  one  part  of 
iodide  of  silver.  It  is  soluble  to  a  large  extent,  at  the  boiling 
temperature,  in  concentrated  solutions  of  the  alkaline  and 
earthy  iodides,  and  forms  with  them  double  salts. 

Silver  is  rapidly  dissolved  by  hydriodic  acid,  ^vith  evolution 


SALTS   OF    SILVER.  339 

of  hydrogen.  If  the  action  is  assisted  by  heat,  the  solution 
deposits,  on  cooling,  a  colourless  crystalline  salt,  resembling 
nitrate  of  silver,  but  decomposing  as  soon  as  it  is  sepa- 
rated from  the  liquid  :  it  appears  to  consist  of  an  iodide  of 
silver  and  hydrogen.  The  mother-liquor,  when  left  to  itself, 
deposits  iodide  of  silver  in  large  regular  six-sided  prisms, 
resembling  the  native  iodide  (H.  Ste.-Claire  Deville).* 

Fluoride  of  silver,  AgF,  is  obtained  by  dissolving  the  oxide 
or  carbonate  in  hydrofluoric  acid.  It  is  very  soluble  in  water, 
and  is  partly  decomposed  by  evaporation. 

Cyanide  of  silver,  AgCy;  134  or  1675. —  This  salt  contains, 
in  100  parts,  19*41  cyanogen  and  8059  silver.  It  falls  as  a 
white  powder  when  hydrocyanic  acid  is  added  to  a  solution  of 
nitrate  of  silver.  It  is  distinguished  from  chloride  of  silver 
by  dissolving  in  concentrated  nitric  and  sulphuric  acids,  when 
heated.  It  is  readily  decomposed  by  hydrochloric  acid,  and 
yields  hydrocyanic  acid,  100  parts  of  cyanide  of  silver  giving 
20-36  parts  of  hydrocyanic  acid.  It  is  decomposed  by  a  red 
heat,  giving  off  half  its  cyanogen  and  leaving  paracyanide  of 
silver,  AggCya-  Cyanide  of  silver  is  dissolved  by  cyanide 
of  potassium,  and  other  soluble  cyanides.  The  double  cy- 
anide of  potassium  and  silver  crystallises  in  octohedrons, 
KCy.AgCy. 

Carbonate  of  silver,  AgO .  CO2,  is  a  white  insoluble  powder. 

Sulphate  of  silver,  AgO.SOaJ  156  or  1950.— Obtained  by 
dissolving  silver,  with  heat,  in  concentrated  sulphuric  acid,  or 
by  precipitating  a  solution  of  nitrate  of  silver  with  sulphate 
of  potash.  It  is  soluble  in  88  times  its  weight  of  boiling 
water,  and  crystallises,  on  cooling,  in  the  form  of  anhydrous 
sulphate  of  soda.  This  salt  is  highly  soluble  in  ammonia, 
and  gives,  by  evaporation,  an  ammoniacal  sulphate  of  silver 
in  fine   transparent   crystals,  which   are  persistent  in  air; 

AgO.SOg  +  2NH3,  or  NHalNHJAg  .  SO4.      Chromate  and 

*  Compt.  rend.  xlii.  894. 


340  SILVER. 

seleniate  of  silver  form  analogous  compoands  with  am- 
monia, which  are  all  isomorphous.  The  bichromate  of  silver 
is  also  isomorphous  with  bichromate  of  soda. 

Hyposulphate  of  silver ^  AgO .  S2O5,  is  soluble  in  water,  and 
crystallises  in  the  same  form  ;is  hyposulphate  of  soda.  It 
crystallises  also  with  ammonia,  as  AgO .  S20g  -f  2NIi3,  or 

Hyposulphite  of  silver,  AgO  .  SjOg. —  Hyposulphurous  acid 
appears  to  have  a  greater  affinity  for  oxide  of  silver  than  for 
any  other  base.  Oxide  of  silver  decomposes  the  alkaline 
hyposulphites,  liberating  one-half  of  their  alkali,  and  forming 
a  double  hyposulphite  of  the  alkali  and  silver.  These  double 
salts  are  best  prepared  by  adding  chloride  of  silver  in  small 
portions  to  the  soluble  hyposulphite  of  potash,  soda,  ammonia, 
or  lime  in  the  cold,  till  the  liquid  is  saturated ;  after  w  hich, 
the  solution  is  filtered,  and  mixed  with  a  large  quantity  of 
alcohol,  which  precipitates  the  double  salt;  the  potash  and 
soda  salts  are  crystallisable.  Herschel  considers  the  double 
salts  obtained  in  this  manner  as  probably  containing  one  eq. 
of  hyposulphite  of  silver  to  two  eq.  of  the  other  hyposulpliite. 
The  solution  of  one  of  these  double  salts  dissolves  more  oxide 
of  silver,  and  forms  a  double  salt,  which  is  believed  to 
contain  single  equivalents  of  the  salts,  and  precipitates  as  a 
white  crystalline,  pulverulent,  bulky  mass.  The  second  com- 
pound is  sparingly  soluble  in  water,  but  dissolves  in  ammonia, 
and  communicates  to  the  liquor  an  intensely  sweet  taste. 

The  hyposulphite  of  silver  itself  is  an  insoluble  substance ; 
it  is  prone  to  undergo  decomposition,  changing  spontaneously 
into  sulphate  and  sulphide  of  silver.  When  to  a  dilute  solu- 
tion of  nitrate  of  silver,  a  dilute  solution  of  hyposulphite  of 
soda  is  added  by  small  quantities,  a  white  precipitate  of  hypo- 
sulphite of  silver  falls,  which  dissolves  again  in  a  few  seconds, 
from  the  formation  of  the  soluble  double  hyposulphite  of  soda 
and  silver.     When  enough  of  hyposulphite  of  soda  has  been 


NITRATE    OF    SILVER.  341 

gradually  added  to  render  the  precipitate  permanent,  without, 
however,  decomposing  the  whole  silver  salt,  a  flocculent  mass 
is  obtained  of  a  dull  grey  colour,  which  is  permanent.  The 
liquor  contains  much  hyposulphite  of  silver,  and  has  an  in- 
tensely sweet  taste,  not  at  all  metallic ;  the  silver  is  not  pre- 
cipitated from  it  by  hydrochloric  acid  or  the  chlorides.  An 
excess  of  hyposulphite  of  soda  destroys  the  precipitated  hypo- 
sulphite of  silver,  converting  it  into  sulphide  of  silver. 

Nitrate  of  silver,  AgO  .  NO5;  170  or  2125, — When  a  piece 
of  pure  silver  is  suspended  in  nitric  acid,  it  dissolves  for  a 
time  without  effervescence  at  a  low  temperature,  nitrous  acid 
being  produced,  which  colours  the  liquid  blue ;  but  if  heat  be 
applied  or  the  temperature  allowed  to  rise,  then  the  metal  dis- 
solves with  violent  effervescence,  from  the  escape  of  nitric 
oxide.  The  nitrate  of  silver  crystallises  on  cooling  in  colour- 
less tables,  which  are  anhydrous.  It  is  soluble  in  1  part  of 
cold,  in  \  part  of  hot  water,  and  in  4  parts  of  boiling  alcohol. 
The  solution  of  this  salt  does  not  redden  litmus  paper,  like 
most  metallic  salts,  but  is  exactly  neutral.  Nitrate  of  silver 
fuses  at  426°,  and  forms  a  crystalline  mass  on  cooling ;  it  is 
cast  into  little  cylinders  for  the  use  of  surgeons.  It  is  some- 
times adulterated  in  this  state  with  nitrate  of  potash,  which 
may  be  detected  by  the  alkaline  residue  which  the  salt  then 
leaves  when  heated  before  the  blowpipe,  —  or  with  nitrate  of 
lead,  in  which  case  the  solution  of  the  salt  is  precipitated  by 
iodide  of  potassium,  of  a  full  yellow  colour.  When  applied  to 
the  flesh  of  animals,  it  instantly  destroys  the  organisation  and 
vitality  of  the  part.  It  forms  insoluble  compounds  with  many 
kinds  of  animal  matter,  and  is  employed  to  remove  it  j&'om 
solution.  When  organic  substances,  to  which  a  solution  of 
nitrate  of  silver  has  been  applied,  are  exposed  to  light,  they 
become  black  from  the  reduction  of  the  oxide  of  silver  to  the 
metallic  state.  A  solution  of  nitrate  of  silver  in  ether  is  em- 
ployed to  dye  the  hair  black.  One  part  of  nitrate  of  silver 
and  4  parts  of  gum  arable  dissolved  in  4  parts  of  water,  and 


342  SILVER. 

blackened  with  a  small  quantity  of  Indian  ink,  form  the  inde- 
lible marking  ink  used  to  write  upon  linen.  The  part  of  the 
linen  to  be  marked  should  be  first  wetted  with  a  solution  of 
carbonate  of  soda  and  dried,  and  the  writing  should  be  exposed 
to  the  light  of  the  sun.  For  this  ink,  which  is  expensive,  another 
liquid  has  been  substituted  by  bleachers,  namely  coal  tar,  made 
sufficiently  thin  with  naphtha  to  write  with,  which  is  found  to 
resist  chlorine,  and  to  answer  well  as  a  marking  ink. 

A  strong  solution  of  nitrate  of  silver  absorbs  two  equivalents 
of  ammoniacal  gas,  and  forms  the  crystallisable  Ammoniacal 

nitrate  of  silver,  AgO  .NOg-f  2NH3=N  H^lNIIJAg'.NOe. 
The  dry  nitrate  in  powder  absorbs  three  atoms  of  ammonia, 

AgO.N06  +  3NH3=NH(NHj2Ag\  NOg. 

Nitrate  of  silver  forms  a  double  salt  with  nitrate  of  the  red 
oxide  of  mercury,  which  crystallises  in  prisms.  Nitrate  of 
silver  and  cyanide  of  mercury  also  form  a  double  salt,  when 
hot  solutions  of  them  are  mixed  :  AgO.N05  +  2HgCy  +  8HO. 
Cyanide  of  silver  is  soluble  in  a  boiling  solution  of  nitrate  of 
silver,  and  forms  a  crystalline  compound,  AgO .  NO5  +  2 AgCy, 
which  is  decomposed  by  water. 

Nitrite  of  silver,  AgO  .  NO3  ;  154  or  1925. —  Nitrate  of 
soda  is  fused  at  a  red  heat,  till  it  is  wholly  converted  into  ni- 
trite by  loss  of  oxygen ;  the  latter  salt  then  begins  to  give  off 
nitrous  acid,  and  a  small  portion  of  the  salt  dissolved  in  water 
will  be  found  to  precipitate  silver  brown.  The  fusion  is  then 
interrupted,  the  salt  dissolved  in  boiling  water,  precipitated 
by  nitrate  of  silver,  and  filtered  while  still  very  hot.  The 
nitrite  of  silver,  which  requires  120  times  its  weight  of  water 
at  60°  to  dissolve  it,  is  precipitated  as  the  solution  cools.  The 
other  nitrites  are  prepared  by  rubbing  this  salt  in  a  mortar 
with  chlorides  taken  in  equivalent  quantities.  It  appears 
from  experiments  of  Proust,  that  two  subnitrites  of  silver 
exist,  one  soluble  and  the  other  insoluble. 

Acetate  of  silver,  wliich  is  soluble  in  100  times  its  weight 


ALLOYS    OF    SILVER.  343 

of  cold  water,  is  precipitated  when  acetate  of  copper  is  mixed 
witli  a  concentrated  solution  of  nitrate  of  silver.  It  crys- 
tallises from  solution  in  boiling  water  in  anhydrous  needles. 

Oxalate  of  silver  is  an  insoluble  powder.  A  double  oxalate 
of  potash  and  silver  is  formed  by  saturating  binoxalate  of 
potash  with  carbonate  of  silver.  It  is  very  soluble,  and 
forms  rhomboidal  crystals,  which  are  persistent  in  air. 

Peroxide  of  silver. — A  superior  oxide  of  silver  is  deposited 
upon  the  positive  pole  or  zincoid  of  a  voltaic  battery  in  a 
weak  solution  of  nitrate  of  silver,  in  the  form  of  needles  of 
3  or  4  lines  in  length,  which  are  black  and  have  a  metallic 
lustre,  while  metallic  silver  is,  at  the  same  time,  deposited  in 
crystals  upon  the  negative  pole  or  chloroid.  The  former 
crystals  are  converted  by  sulphuric  acid  into  oxide  of  silver 
and  oxygen,  and  yield  with  hydrochloric  acid,  chloride  of 
silver  and  chlorine.  According  to  Fischer,  whose  observa- 
tions are  confirmed  by  L.  Gmelin,  the  peroxide  prepared  as 
above  from  nitrate  of  silver  always  retains  nitric  acid,  and  if 
prepared  in  a  similar  manner  from  the  sulphate,  it  always 
retains  sulphuric  acid.* 

Alloys  of  silver. — Silver  may  be  readily  alloyed  with  most 
metals.  It  combines  by  fusion  with  iron,  from  which  it 
cannot  be  separated  by  cupellation.  Native  silver  is  always 
associated  with  gold ;  the  two  metals  are  found  crystallised 
together  in  all  proportions  in  the  same  cubic  or  octohedral 
crystals.  Gold  may  be  detected  in  a  silver  coin,  by  dissolving 
the  latter  in  pure  nitric  acid,  when  a  small  quantity  of  black 
powder  remains,  which  after  being  washed  with  water,  will 
be  found  to  dissolve  in  nitro-hydrochloric  acid,  giving  a 
yellow  solution,  in  which  protochloride  of  tin  produces  a  pre- 
cipitate of  the  purple  powder  of  Cassius.  Pure  silver,  being 
very  soft,  is  always  alloyed  in  coin  and  plate,  with  a  certain 

*  Gmelin's  Handbook,  Translation,  vi.  145. 


344  SILVER. 

quantity  of  copper,  to  make  it  harder.  The  standard  silver 
of  England  is  an  alloy  of  222  pennyweights  of  silver  with 
18  pennyweights  of  copper.,,  or  it  contains  92*5  per  cent,  of 
silver.  The  standard  of  the  Spanish  dollar,  of  the  French  and 
most  other  coinages,  is  90  per  cent,  of  silver.  The  alloy  of 
silver  and  copper  of  greatest  stability  consists  of  71*9  silver, 
and  28"  1  copper,  and  corresponds  with  the  formida  AgCu^.^ 

ESTIMATION     OF     SILVER,     AND     METHODS     OF     SEPARATING     IT 
FROM    OTHER    METALS. 

Silver,  when  in  the  state  of  solution,  is  always  estimated  as 
chloride.  The  solution,  if  not  already  acid,  is  slightly  acidu- 
lated with  nitric  acid;  the  silver  precipitated  with  hydro- 
chloric acid,  and  the  liquid  placed  for  some  hours  in  a  warm 
situation  to  cause  the  precipitated  chloride  of  silver  to  settle 
down.  The  precipitate  is  collected  on  a  filter,  which  should 
be  as  small  as  possible,  washed  with  water,  and  dried  at  212°. 
It  must  then  be  separated  as  completely  as  possible  from 
the  filter;  introduced  into  a  porcelain  crucible,  previously 
weighed ;  the  filter  burnt  to  ashes  outside  the  crucible ;  the 
ashes  added  to  the  contents  of  the  crucible ;  and  the  whole 
strongly  heated  over  a  lamp  till  the  chloride  of  silver  is 
brought  to  a  state  of  tranquil  fusion,  after  which  it  is  left  to 
cool  and  weighed.  It  contains  75-2G  per  cent,  of  silver. 
This  mode  of  estimation  is  affected  with  an  error,  arising 
from  the  partial  reduction  of  the  chloride  of  silver  by  the 
organic  matter  of  the  filter.  The  error  thus  occasioned  is 
but  slight  when  the  process  is  well  conducted,  and  may 
always  be  obviated  by  treating  the  fused  chloride  after  cool- 
ing  with  nitric  acid  to  dissolve  the  reduced  silver;  then 
adding  hydrochloric  acid,  evaporating  to  dryness,  and  again 
fusing  the  residue.  Another  mode  of  proceeding  is  to  collect 
the  chloride  of  silver  on  a  weighed  filter,  and  dry  it  in  an  oil- 

■   *  Levol,  Ann.  Ch.  Phys.  [3],  xxxvi.  220. 


ESTIMATION   OF   SILVER.  345 

bath,  at  about  300°  P.  The  chloride  may  also  be  washed  by 
decantation,  and  the  use  of  a  filter  avoided  altogether ;  but 
the  washing  requires  very  careful  manipulation. 

The  quantity  of  silver  in  a  solution  may  also  be  determined 
by  precipitating  it  with  a  solution  of  chloride  of  sodium  of 
known  strength.  The  solution  of  chloride  of  sodium  is  made 
of  such  a  strength  that  a  cubic  decimetre  of  it  exactly  pre- 
cipitates 1  gramme  of  pure  silver.  It  is  added  to  the  silver 
solution  from  a  burette,  divided  into  cubic  centimetres,  the 
liquid  being  well  shaken  after  each  addition,  to  cause  the 
precipitate  to  settle  down.  The  number  of  cubic  centimetres 
of  solution  thus  added  determines  the  quantity  of  silver 
present. 

As  silver  is  reduced  from  many  of  its  salts  by  the  mere 
action  of  heat,  the  quantity  of  silver  in  such  compounds  may 
be  readily  determined  by  simply  igniting  them  in  a  porcelain 
crucible.  This  method  is  applicable  to  nearly  all  salts  of 
silver  which  contain  organic  acids.  It  must  be  observed, 
however,  that  in  some  cases,  a  certain  quantity  of  carbon  re- 
mains combined  with  the  silver,  and  that  some  organic  silver 
compounds  containing  nitrogen  leave  cyanide  of  silver  when 
ignited. 

The  method  of  precipitating  by  hydrochloric  acid  serves 
to  separate  silver  from  all  other  metals.  If  lead  be  present 
in  solution  with  silver,  the  liquid  must  be  diluted  with  a  large 
quantity  of  water  before  the  hydrochloric  acid  is  added; 
because  the  chloride  of  lead  is  but  sparingly  soluble.  The 
separation  of  silver  from  lead  may  also  be  effected  by  pre- 
cipitating both  the  metals  as  chlorides,  and  dissolving  the 
chloride  of  silver  in  ammonia.  To  separate  silver  from  mer- 
cury, the  latter  metal,  if  in  the  state  of  mercurous  oxide, 
must  first  be  converted  into  mercuric  oxide  by  oxidation  with 
nitric  acid. 

The  estimation  of  the  quantity  of  silver  in  alloys,  such  as 
coins,  is  usually  effected  either  by  cupellation  in  the  manner 


34()  GOLD. 

already  described  (p.  332.),  or  by  dissolving  the  alloy  in  nitric 
acid,  and  precipitating  the  silver  with  a  graduated  solution  of 
chloride  of  sodium.* 

The  cupellation  of  silver  is  always  attended  with  a  certain 
loss,  arising  partly  from  a  portion  of  the  melted  silver  being 
absorbed  by  the  cupel,  and  partly  by  volatilisation.  The  loss 
thus  occasioned  varies  with  the  proportion  of  lead  employed 
in  the  cupellation,  with  the  proportion  of  silver  in  the  aUoy, 
and  likewise  with  the  heat  of  the  furnace  :  hence  the  results 
obtained  require  a  certain  correction,  the  amount  of  which 
must  be  determined  by  special  trials  made  upon  alloys  of  known 
composition  and  with  different  proportions  of  lead. 


SECTION    III. 

GOLD. 

Eq.  98-33  or  1229*16;  Au.  (Aurum.) 

Gold  is  found  in  small  quantity  in  most  countries,  some- 
times mixed  with  iron  pyrites,  copper  pyrites,  and  galena,  but 
generally  native,  massive,  and  disseminated  in  threads  through 
crystalline  rocks,  such  as  quartz,  or  in  grains  among  the  sand 
of  rivers,  and  in  allmial  deposits  formed  by  the  disintegration 
of  ancient  rocks.  In  these  deposits,  some  of  which  are  of 
great  extent,  gold  is  occasionally  found  in  masses  of  consider- 
able size,  called  iiuggets.  Formerly,  the  principal  supply  of 
this  metal  was  from  the  mines  of  South  America,  Ilungarj^, 
and  the  Uralian  mountains;  but  of  late  years,  the  largest 
quantities  have  been  obtained  from  California  and  Australia. 
Native  gold  is  sometimes  pure,  but  is  more  frequently  asso- 
ciated in  various  proportions  with  silver. 

*  The  process,  by  Guy-Lussac,  for  lliis  purpose  is  described,  with  the  re- 
quisite Tables,  in  the  Parhaniciitary  Keport  upon  the  Koyal  Mint,  1837, 
Appendix,  p.  145.     See  also  Dr.  Mdler's  Elemcuis  of  Chemistry^  p.  1035. 


GOLD.  '  347 

Gold  is  separated  from  the  substances  with  which  it  is  me- 
chanically associated,  either  by  washing  with  water,  whereby 
the  earthy  matters  are  carried  away  while  the  heavy  gold 
particles  remain  behind,  or  by  amalgamation.  The  small 
quantity  of  gold  which  occurs,  generally  associated  with 
silver,  in  certain  lead  and  copper  ores,  is  extracted  by  liqua- 
tion and  cupellation,  in  the  manner  already  described  for 
silver.  By  these  processes,  gold  is  obtained  free  from  all 
other  metals  except  silver,  and  from  this  it  may  be  separated 
by  nitric  acid,  which  dissolves  the  silver,  but  only  when  it 
forms  a  large  proportion  of  the  alloy.  When  nitric  acid  does 
not  dissolve  the  silver,  the  alloy  is  submitted  to  an  operation 
termed  quartation,  which  consists  in  fusing  it  with  four  times 
its  weight  of  silver,  after  which  the  whole  of  the  silver  may 
be  dissolved  out  by  nitric  acid. 

Pure  gold  may  be  obtained  from  any  alloy  containing  it, 
by  dissolving  the  alloy  in  a  mixture  of  two  measures  of  hy- 
drochloric and  one  measure  of  nitric  acid;  separating  the 
solution  from  insoluble  chloride  of  silver  by  filtration ;  eva- 
porating it  over  the  water-bath  till  acid  vapours  cease  to  be 
exhaled ;  then  dissolving  the  residue  in  water  acidulated  with 
hydrochloric  acid;  and  adding  protosulphate  of  iron,  which 
completely  precipitates  the  gold  in  the  form  of  a  brown  or 
brownish-yellow  powder,  the  protosulphate  of  iron  being  at 
the  same  time  converted  into  sesquisulphate  and  sesqui- 
chloride : 

6(FeO  .  SO3)  +  AU2CI3  =  2(Fe203  .  3SO3)  +  re2Cl3  +  2Au. 

The  gold  thus  precipitated  is  quite  destitute  of  metallic  lustre, 
but  acquires  that  character  by  burnishing. 

From  alloys  of  gold  and  silver,  or  of  gold,  silver,  and 
copper,  the  gold  may  also  be  separated  by  the  action  of  strong 
sulphuric  acid.  The  alloy,  after  being  granulated  by  pouring 
it  in  the  melted  state  into  water,  is  heated  in  a  platinum  or 
cast-iron  vessel  with  2  J  times  its  weight  of  sulphuric  acid 

VOL.  II.  B  B 


348  GOLD. 

of  specific  gravity  1*815  (66°  Baume),  the  heat  being  con- 
tinued as  long  as  sulphurous  acid  is  evolved.  The  silver  and 
copper  are  thereby  converted  into  sulphates,  while  the  gold 
remains  unattacked.  The  solution  is  boiled  for  a  quarter  of 
an  hour  with  an  additional  quantity  of  sulphuric  acid  of 
specific  gravity  1*653,  or  58°  Bauni6  (obtained  by  concen- 
trating the  acid  mother-liquors  of  sulphate  of  copper  pro- 
duced in  the  operation),  and  afterwards  left  at  rest.  The 
gold  then  settles  down,  and  the  liquid,  after  being  diluted 
with  water,  is  transferred  to  a  leaden  vessel  and  again  boiled 
with  sheets  of  copper  immersed  in  it.  The  silver  is  then 
precipitated  in  the  metallic  state,  while  the  copper  is  con- 
verted into  sulphate,  and  dissolves.  The  gold  deposited  in 
the  manner  above  described  still  retains  a  small  quantity  of 
silver,  from  which  it  is  separated  by  treating  it  a  second  and 
a  third  time  with  strong  sulphuric  acid  :  it  then  retains  only 
0*005  of  silver.  This  process  is  not  applicable  to  alloys  con- 
taining more  than  20  per  cent,  of  gold ;  richer  alloys  must 
first  be  fused  with  the  requisite  quantity  of  silver.  It  is 
applied  on  the  large  scale  to  the  extraction  of  gold,  chiefly 
from  alloys  which  contain  but  little  of  that  metal,  such  as 
native  silver  and  old  silver  coins,  and,  as  now  practised,  is 
economically  available  even  when  the  amount  of  gold  does  not 
exceed  one  part  in  2000. 

Gold  is  the  only  metal  of  a  yeUow  colour.  When  pure,  it 
is  more  malleable  than  any  other  metal,  and  nearly  as  soft  as 
lead.  Its  ductility  appears  to  have  scarcely  a  limit.  A  single 
grain  of  gold  has  been  drawn  into  a  wire  500  feet  in  length, 
and  this  metal  is  beaten  out  into  leaves  which  have  not  more 
than  1 -200,000th  of  an  inch  of  thickness.  The  coating  of 
gold  on  gilt  silver  wire  is  still  thinner.  Gold,  when  very  thin, 
is  transparent,  thin  gold  leaf  appearing  green  by  transmitted 
light.  The  green  colour  passes  into  a  ruby  red  when  highly 
attenuated  gold  is  heated :  in  the  red  gold-glass,  the  gold  is  in 
the   metallic   state  (Faraday).     The  point  of  fusion  of  this 


AUROUS    COMPOUNDS.  349 

metal  is  2192°,  according  to  Pouillet;  2518°,  according  to 
Guy ton-Morveau ;  and  2590°,  according  to  Daniell :  it  con- 
tracts considerably  upon  becoming  solid.  The  density  of  gold 
varies  from  19*258  to  19-367,  according  as  it  has  been  more 
or  less  compressed.  Gold  does  not  oxidate  or  tarnish  in  air, 
at  the  usual  temperature,  nor  when  strongly  ignited.  Bat 
this  and  the  other  noble  metals  are  dissipated  and  partly 
oxidated,  when  a  powerful  electric  charge  is  sent  through 
them  in  thin  leaves.  It  is  not  dissolved  by  nitric,  hydro- 
chloric, or  sulphuric  acid,  or  indeed  by  any  single  acid.  It  is 
acted  upon  by  chlorine,  which  converts  it  into  sesquichloride, 
and  by  acid-mixtures,  such  as  aqua-regia,  which  evolve  chlo- 
rine. It  combines  in  two  proportions  with  oxygen,  forming 
the  two  oxides  AuqO  and  AU2O3,  which  show  but  little 
tendency  to  combine  with  acids.  Some  chemists,  however, 
double  the  atomic  weight  of  gold,  and  regard  these  oxides  as 
protoxide,  AuO,  and  teroxide,  AUO3,  respectively. 

Oxide  of  gold,  Aurous  oxide,  AU2O,  204i'66  or  2558*25. — 
This  oxide  is  obtained  as  a  green  powder  by  decomposing  the 
corresponding  chloride  of  gold  with  a  cold  solution  of  potash. 
It  is  partly  dissolved  by  the  alkali,  and  soon  begins  to  un- 
dergo decomposition,  being  resolved  into  the  higher  oxide  and 
metallic  gold.  The  latter  forms  upon  the  sides  of  the  vessel 
a  thin  film,  which  is  green  by  transmitted  light,  like  gold 
leaf. 

Chloride  of  gold,  Aurous  chloride,  AU2CI,  is  obtained  by 
evaporating  a  solution  of  the  sesquichloride  to  dryness,  and 
heating  the  powder  thus  obtained  in  a  sand-bath,  retaining  it 
at  about  the  temperature  of  melting  tin,  and  constantly 
stirring  it,  so  long  as  chlorine  is  evolved.  It  is  a  white,  saline 
mass,  having  a  tinge  of  yellow,  and  quite  insoluble  in  water. 
In  the  dry  state  it  is  permanent,  but  in  contact  with  water  it 
gradually  undergoes  decomposition,  and  is  converted  into 
gold  and  the  sesquichloride.  This  change  takes  place  almost 
instantaneously  at  the  boiling  temperature. 

B  B  2 


350  GOLD. 

Aurous  iodide,  Auol,  is  formed  by  the  action  of  hydriodic 
acid  on  auric  oxide,  water  being  formed  and  two-tbirds  of  tbe 
iodine  set  free : 

AU2O3  +  SHI  =  AU2I  +  3H0  +  21; 

also  by  adding  iodide  of  potassium  in  proper  proportion,  and 
in  successive  small  quantities,  to  an  aqueous  solution  of  auric 
chloride : 

AU2CI3  +  SKI  =  Au^I  -f  3KC1  +  21. 

It  is  a  lemon-yellow,  crystalline  powder,  insoluble  in  cold 
water,  and  very  sparingly  soluble  in  boiling  water. 

Aurous  sulphide  is  formed  when  hydrosulphuric  acid  gas  is 
passed  into  a  boiling  solution  of  the  sesqui chloride  of  gold. 
It  is  dark-brown,  almost  black.  Aurous  sulphide  combines 
with  the  protosulphides  of  potassium  and  sodium,  forming 
double  salts  containing  1  eq.  of  aurous  sulphide  with  1  eq.  of 
the  alkaline  sulphide.  The  sodium- salt  is  obtained  by  fusing 
together  2  eq.  protosulphide  of  sodium,  1  eq.  gold,  and  6  eq. 
sulphur;  digesting  the  fused  mass  in  water;  filtering  the 
yellow  solution  in  an  atmosphere  of  nitrogen  ;  and  concen- 
trating in  vacuo  over  sulphuric  acid.  Yellow  crystals  are 
then  obtained,  having  the  form  of  oblique  hexagonal  prisms 
with  trilateral  or  quadrilateral  summits,  and  containing 
NaS  .  Au^S  -I-  8Aq.  They  are  soluble  in  water  and  alcohol. 
The  potassium-salt,  which  is  obtained  in  a  similar  manner, 
forms  indistinct  crystals  (Col.  Yorke).* 

Sesquioxide  of  gold,  Auric  oxide,  AU2O3,  220*66  or  2758'25. 
—  This  oxide  has  many  of  the  properties  of  an  acid.  It  is 
obtained  by  digesting  magnesia  in  a  solution  of  sesquichloride 
of  gold,  when  an  insoluble  compound  of  auric  oxide  and  mag- 
nesia is  formed,  which  is  collected  upon  a  filter  and  weL 
washed.  The  compound  is  afterwards  digested  in  nitric  acid, 
which  dissolves  the  magnesia,  with  traces  of  auric  oxide,  but 

*  Cliem.  Soc.  Qu.  J.  i.  236. 


AUROUS    COMPOUNDS.  351 

leaves  the  greater  part  of  the  latter  undissolved.  It  is  left 
in  the  state  of  a  reddish-yellow  hydrate,  which  when  dried  in 
air  becomes  chestnut-brown.  When  precipitated  by  an  alkali, 
auric  oxide  carries  down  a  portion  of  the  latter,  of  which  it 
may  be  deprived  by  nitric  acid.  Dried  at  212°,  it  abandons 
its  water,  becomes  black,  and  is  in  part  reduced.  When 
exposed  to  light,  particularly  to  the  direct  rays  of  the  sun,  its 
reduction  is  very  rapid.  It  is  decomposed  by  an  incipient 
red  heat.  Hydrochloric  acid  is  the  only  acid  which  dissolves 
and  retains  this  oxide,  and  then  sesquichloride  of  gold  is 
formed.  It  is  dissolved  by  concentrated  nitric  and  sulphuric 
acid,  but  precipitated  from  these  solutions  by  water.  The 
affinity  of  this  oxide  for  'alkaline  oxides,  on  the  contrary,  is  so 
great  that,  when  boiled  in  a  solution  of  chloride  of  potassium, 
it  is  dissolved,  the  liquid  becoming  alkaline,  and  aurate  of 
potash,  or  a  compound  of  auric  oxide  and  potash,  being  formed. 
The  compounds  of  auric  oxide  with  the  alkalies  and  alkaline 
oxides  are  nearly  colourless,  and  are  not  decomposed  by  water. 
They  appear  to  be  of  two  different  degrees  of  saturation, 
aurates  which  are  soluble,  and  superaurates  which  are  in- 
soluble. The  only  one  of  these  compounds  which  has  been 
studied  in  some  degree  is  the  aurate  of  ammonia,  or  ful- 
minating gold  as  it  is  named,  from  its  violently  explosive 
character. 

Aurate  of  ammonia. — When  the  solution  of  gold  is  precipi- 
tated by  a  small  quantity  of  ammonia,  a  powder  of  a  deep 
yellow  colour  is  obtained,  which  is  a  compound  of  aurate  of 
ammonia  with  a  portion  of  sesquichloride  of  gold.  This  com- 
pound explodes  by  heat,  but  the  detonation  is  not  strong. 
But  when  the  solution  of  gold  is  treated  with  an  excess  of 
ammonia,  and  the  precipitate  well  washed  by  ebullition  in  a 
solution  of  ammonia,  or  better  in  water  containing  potash, 
the  fulminating  gold  has  a  yellowish  brown  colour  with  a 
tinge  of  purple.  When  dry,  it  explodes  very  easily  with  a 
loud  report,  accompanied  by  a  feeble  flame.     It  may  be  ex- 

B  B  3 


352  GOLD. 

ploded  by  a  heat  a  little  above  the  boiling  point  of  water,  or 
by  the  blow  of  a  hammer.  Its  composition  has  not  been 
exactly  determined ;  but  if  the  ammonia  is  present  in  double 
the  proportion  that  would  contain  the  hydrogen  necessary  to 
bum  the  oxygen  of  the  auric  oxide,  which  Berzelius  considers 
probable,  its  constituents  may  be  AU2O3  .  2NH3  H  HO.  The 
affinity  of  auric  oxide  for  ammonia  is  so  great,  that  it  takes 
that  alkali  from  all  acids.  Thus,  when  auric  oxide  is  digested 
in  sulphate  of  ammonia,  fulminating  gold  is  formed,  and  the 
liquid  becomes  acid. 

Aurate  of  potash,  KO  .  Au^Og  +  6H0. — Obtained  in  the 
crystalline  state  by  evaporating  a  solution  of  sesquioxide  of  gold 
in  a  slight  excess  of  pure  potash,  first  over  the  open  fire  and 
afterwards  in  vacuo :  the  crystals  may  be  freed  from  adhering 
potash  by  recrystallisation  from  water,  then  drained  on  un- 
glazed  porcelain  and  dried  in  vacuo.  Aurate  of  potash  is 
very  soluble  in  water,  and  forms  a  yellowish  strongly  alkaline 
solution,  which  is  decomposed  by  nearly  all  organic  bodies,  the 
gold  being  precipitated  in  the  metallic  state  :  it  is  also  de- 
composed by  heat.  With  most  metallic  salts  it  forms  pre- 
cipitates of  aurates,  which  are  insoluble  in  water,  but  soluble 
in  excess  of  the  precipitant ;  thus,  chloride  of  calcium  forms 
a  precipitate  of  aurate  of  lime,  soluble  in  excess  of  chloride  of 
calcium.  The  solution  of  aurate  of  potash  may  be  used  as  a 
bath  for  electro-gilding. 

Aurosulphite  of  potash,  KO.  Au203  +  4(KO  .  2SO2)  +  5H0 ; 

or  5K0LgX  3  4-  5 HO.  —  Deposited    in    beautiful    yellow 

needles  when  sulphite  of  potash  is  added  drop  by  drop  to  an 
alkaline  solution  of  aurate  of  potash.  It  is  nearly  insoluble  in 
alkaline  solutions,  but  dissolves  with  decomposition  in  pure 
water,  especially  if  hot,  giving  off  sulphurous  acid  and  de- 
positing metallic  gold.  Acids  decompose  it  in  a  similar 
manner.  After  drying  in  vacuo,  it  may  be  preserved  for  two 
or  three  months,  in  well-closed  bottles,  but  ultimately  decom- 


PURPLE    OP    CASSIUS.  353 

poses_,  giving  off  sulphurous  acid  and  leaving  metallic  gold  and 
sulphate  of  potash.  The  same  decomposition  takes  place 
more  quickly  when  the  salt  is  heated  (Fremy).* 

Purple  of  Cassius. — When  protochloride  of  tin  is  added  to 
a  dilute  solution  of  gold^  a  purple- coloured  powder  falls,  which 
has  received  that  name.  It  is  obtained  of  a  finer  tint  when 
protochloride  of  tin  is  added  to  a  solution  of  the  sesquichloride 
of  iron,  till  the  colour  of  the  liquid  takes  a  shade  of  green,  and 
the  liquid  in  that  state  added,  drop  by  drop,  to  a  solution  of 
sesquichloride  of  gold  free  from  nitric  acid,  and  very  dilute. 
After  24  hours,  a  brown  powder  is  deposited,  which  is  slightly 
transparent  and  purple-red  by  transmitted  light.  When  dried 
and  rubbed  to  powder,  it  is  of  a  dull  blue  colour.  Heated  to  red- 
ness, it  loses  a  little  water,  but  no  oxygen,  and  retains  its  former 
appearance.  If  washed  with  ammonia  on  the  filter  while  still 
moist,  it  is  dissolved,  and  a  purple  liquid  passes  thi'ough, 
which  rivals  the  hypermanganate  of  potash  in  beauty.  From 
this  liquid,  the  colouring  matter  separates  very  gradually,  weeks 
elapsing  before  the  upper  strata  of  the  liquid  become  colour- 
less ;  but  it  is  precipitated  more  rapidly  when  heated  in  a  close 
vessel  between  140°  and  180°.  The  powder  of  Cassius  is  inso- 
luble in  solutions  of  potash  and  soda.  It  may  also  be  formed 
by  fusing  together  2  parts  of  gold,  3^  parts  of  tin,  and  15  parts 
of  silver,  under  borax,  to  prevent  the  oxidation  of  the  tin,  and 
treating  the  alloy  with  nitric  acid  to  dissolve  out  the  silver ;  a 
purple  residue  is  left  containing  the  tin  and  gold  that  were 
employed. 

The  powder  of  Cassius  is  certainly,  after  ignition,  a  mixture 
of  binoxide  of  tin  and  metallic  gold,  from  which  the  gold  can 
be  dissolved  out  by  aqua-regia,  wliile  the  binoxide  of  tin  is  left ; 
and  the  last  mode  of  preparing  it,  favours  the  idea  that  its 
constitution  is  the  same  before  ignition ;  but  the  solubility  of 
the  unignited  powder  in  ammonia,  and  the  fact  that  mercury 
does  not  dissolve  out  gold  from  the  powder  when  properly 

*  Ann.  Ch.  Pharm.  lyi.  315. 

B  B   4 


854  GOLD. 

prepared,  appear  to  be  conclusive  against  that  opinion.  The 
proportions  of  its  constituents  vary  so  much,  that  there 
must  be  more  than  one  compound ;  or  more  likely  the  colour- 
ing compound  combines  with  more  than  one  proportion  of 
binoxide  of  tin.  Berzelius  proposed  the  theory  that  the  powder 
of  Cassius  may  contain  the  true  protoxide  of  gold  combined 
with  sesquioxide  of  tin,  AuO .  Sn203,  a  kind  of  combination 
containing  an  association  of  three  atoms  of  metal,  which  is 
exemplified  in  black  oxide  of  iron,  spinell,  gahnite,  franklinite, 
and  other  minerals,  and  which  we  have  repeatedly  observed  to 
be  usually  attended  with  great  stability.  A  glance  at  its 
formula  shows  how  readily  the  powder  of  Cassius,  as  tlms  repre- 
sented, may  pass  into  gold  and  binoxide  of  tin ;  AuO  .  Sn203 
=  Au  -f  2Sn02.  The  existence  of  a  purple  oxide  of  gold, 
AuO,  is  not  established ;  but  it  is  probably  the  substance 
formed  when  a  solution  of  gold  is  applied  to  the  skin  or  nails, 
and  which  dyes  them  purple.  Paper,  coloured  purple  by  a 
solution  of  gold,  becomes  gilt  when  placed  in  the  moist  state 
in  phosphuretted  hydrogen  gas,  which  reduces  the  gold  to  the 
metallic  state. 

Pelletier  gives  the  following  method  of  preparing  a 
purple  of  Cassius  of  constant  composition  :  —  20  grammes  of 
gold  are  dissolved  in  100  grammes  of  aqua-regia  containing 
20  parts  nitric  to  80  parts  of  commercial  hydrochloric  acid ; 
the  solution  is  evaporated  to  dryness  over  the  water-bath ;  the 
residue  dissolved  in  water ;  the  filtered  solution  diluted  with 
7  or  8  decilitres  of  water;  and  tin  filings  introduced  into  it: 
in  a  few  minutes  the  liquid  becomes  brown  and  turbid,  and 
deposits  a  purple  precipitate,  which  merely  requires  to  be 
washed  and  dried  at  a  gentle  heat.  The  purple  thus  prepared 
contains  in  100  parts:  32'746  stannic  acid,  14"618  protoxide 
of  tin,  44772  aureus  oxide  (AU2O)  and  7*864  water.  The 
precipitate  obtained  by  treating  sesquichloride  of  gold  with 
pure  protochloride  of  tin  is  always  brown.  To  obtain  a  fine 
purple  precipitate,  the  chloride  of  gold  should  be  treated  with 


AURIC    COMPOUNDS.  855 

a  mixture  of  protochloride  and  bicliloride  of  tin.  The  follow- 
ing process  gives  a  fine  purple  : — a.  A  neutral  solution  is 
prepared  of  1  part  of  tin  in  hydrochloric  acid ;  h.  A  solution 
of  2  parts  tin  in  cold  aqua-regia  (I  part  hydrochloric  acid  to 
3  nitric),  the  liquid  being  merely  heated  towards  the  end  of 
the  process,  that  it  may  not  contain  any  protoxide  of  tin  j 
c.  Seven  parts  of  gold  are  dissolved  in  aqua-regia  (6  hydro- 
chloric to  1  nitric),  and  the  solution,  which  is  nearly  neutral, 
diluted  with  3500  parts  of  water.  To  this  solution  c,  the 
solution  h  is  first  added,  and  then  the  solution  «,  drop  by 
drop,  till  the  proper  colour  is  produced.  If  the  quantity  of  a 
be  too  small,  the  precipitate  is  violet ;  if  too  large,  it  is  brown. 
It  must  be  washed  quickly,  so  that  the  liquid  may  not  act 
upon  it  too  long.     It  weighs  6|  parts  (Bouisson).* 

Sesquisulphide  of  gold,  AU2S3,  or  Auric  sulphide,  is  formed 
when  a  dilute  solution  of  gold  is  precipitated  cold  by  hydro- 
sulphuric  acid.  It  is  a  flocculent  matter  of  a  strong  yellow 
colour,  which  becomes  deeper  by  drying ;  it  loses  its  sulphur 
at  a  moderate  heat. 

Sesquichloride  of  gold,  Perchloride  of  gold,  Auric  chloride, 
AU2CI3,  303*16  or  3789*5.  —  This  compound  is  formed  when 
gold  is  dissolved  in  aqua-regia.  The  solution  is  yellow,  and 
becomes  paler  with  an  excess  of  acid,  but  is  of  a  deep  red 
when  neutral  in  composition.  It  is  obtained  in  the  last 
condition  by  evaporating  the  solution  of  gold,  till  the  liquid 
is  of  a  dark  ruby  colour,  and  begins  to  emit  chlorine. 
It  forms  on  cooling  a  dark  red  crystalline  mass,  which  de- 
liquesces quickly  in  air.  But  the  only  method  of  procuring 
auric  chloride  perfectly  free  from  acid  salt,  is  to  decompose 
aurous  chloride  with  water.  A  compound  of  chloride  of 
gold  and  hydrochloric  acid  crystallises  easily  from  an  acid 
solution,  in  long  needles  of  a  pale  yellow  colour,  which  are 
permanent  in  dry  air,  but  run  into  a  liquid  in  damp  air. 
The  solution  of  this  salt  deposits  gold  on  its  surface,  and 

*  J.  Pharm.  [2],  xvi.  629. 


356  GOLD. 

on  the  side  of  the  vessel  turned  to  the  light.  The  gold  is 
also  precipitated  in  the  metallic  state  by  phosphorus,  by  most 
metals,  by  fen'ous  salts,  by  arsenious  and  antimonious  acids, 
and  by  many  vegetable  and  animal  substances,  by  vegetable 
acids,  by  oxalate  of  potash,  &c.,  carbonic  acid  then  escaping. 
Hydrosulphuric  acid  and  sulphide  of  ammonium  throw  down 
black  sulphide  of  gold,  soluble  in  excess  of  the  latter  re- 
agent. Ammonia  and  carbonate  of  ammonia  produce  a 
yellow  precipitate  of  fulminating  gold.  Potash  added  in 
excess  forms  no  precipitate,  unless  it  contains  organic  matter, 
in  which  case  a  slight  precipitate  of  aurous  oxide  is  pro- 
duced. Cyanide  of  potassium  produces  a  yellow  precipitate 
soluble  in  excess.  Tincture  of  gaUs  throws  down  metallic 
gold.  Chloride  of  gold  is  soluble  in  ether  and  in  some 
essential  oils.  It  forms  double  salts  with  most  other  chlo- 
rides, which  are  almost  all  orange-coloured  when  crystallised ; 
in  efflorescing,  they  acquire  a  lemon-yellow  colour,  but  in 
the  anhydrous  state  they  are  of  an  intense  red.  They  are 
obtained  by  evaporating  the  mixed  solutions  of  the  two  salts. 

Chloride  of  gold  and  potassium,  KCl .  AugCl.^  +  5H0. — 
Crystallises  in  striated  prisms  with  right  summits,  or  in  thin 
hexagonal  tables  which  are  very  efflorescent;  becomes  an- 
hydrous at  212°.  The  anhydrous  salt  fuses  readily  when 
heated,  but  loses  chlorine  and  becomes  a  liquid,  which  is  black 
while  hot,  and  yellow  when  cold.  It  is  then  a  compound  of 
aurous  chloride  with  chloride  of  potassium.  Chloride  of  gold 
and  ammonium  ciystallises  in  transparent  prismatic  needles, 
which  become  opaque  in  air ;  Mr.  Johnston  found  their  com- 
position to  be  NH4CI .  AU2CI3  +  2H0.  Chloride  of  gold  and 
sodium  crystallises  in  long  four-sided  prisms,  and  is  persistent 
in  air.  Its  composition  is  NaCl .  AU2CI3  4-  4H0.  Bonsdorff 
has  prepared  similar  double  salts  with  the  chlorides  of  barium, 
strontium,  calcium,  magnesium,  manganese,  zinc,  cadmium, 
cobalt,  and  nickel.  The  salt  of  lime  contains  sLx,  and  the  salt 
pf  magnesia  twelve  equivalents  of  water. 


AURIC    COMPOUNDS.  357 

Sesquibromide  of  gold,  Au2Br3,  is  formed  by  dissolving  gold 
in  a  mixture  of  nitric  and  hydrobromic  acids.  It  greatly 
resembles  the  sesquichloride,  and  forms  also  an  extensive 
series  of  double  salts. 

Auric  iodide,  AU2I3,  is  formed  by  gradually  adding  a 
neutral  solution  of  auric  chloride  to  a  solution  of  iodide  of 
potassium  :  the  liquid  then  acquires  a  dark-green  colour,  and 
yields  a  dark-green  precipitate  of  Augig,  which  redissolves  on 
agitation;  but  after  1  eq.  of  the  auric  chloride  has  been 
added  to  4  eqs.  of  iodide  of  potassium,  a  farther  addition  of 
the  gold-solution  decolorizes  the  liquid  and  forms  a  permanent 
precipitate  of  auric  iodide,  because  the  iodide  of  gold  and 
potassium  at  first  produced  is  thereby  decomposed.  The 
successive  actions  are  represented  by  the  following  equa- 
tions :  — 

(1.)  4KI  +  AU2CI3  =  3KC1  +  KI .  AU2I3 ; 

(2.)         3(KI .  AU2I3)  +  AU2CI3  =  3KC1  +  4AU2T3. 

Auric  iodide  is  a  very  unstable  compound;  when  exposed 
to  the  air  at  ordinary  temperatures,  it  is  gradually  converted 
into  yellow  aureus  iodide,  and  afterwards  into  metallic  gold. 
It  combines  with  hydriodic  acid  and  with  the  more  basic 
metallic  iodides,  forming  a  series  of  very  dark-coloured  salts ; 
e.  g.  iodo-aurate  of  potassium,  KI .  AU2T3. 

The  oxides  of  gold  show  but  little  tendency  to  combine 
with  oxygen-acids  :  the  sesquioxide  dissolves  in  strong  nitric 
acid,  but  the  solution  is  decomposed  by  evaporation  or  dilu- 
tion. , 

Hyposulphite  of  aurous  oxide  and  soda : 

Au20.S202  +  3(NaO.S202)  +  4HO;  or  ^^^Oj^g^Q^.^  ^jjq 

This  salt  is  prepared  by  mixing  concentrated  solutions  of 
sesquichloride  of  gold  and  hyposulphite  of  soda,  and  preci- 


358  GOLD. 

pitating  with  alcohol.  When  purified  by  repeated  solution  in 
water  and  precipitation  by  alcohol,  it  forms  delicate,  colour- 
less needles.  It  has  a  sweetish  taste,  dissolves  very  easily  in 
water,  but  very  sparingly  in  alcohol.  It  is  decomposed  by 
heat  and  by  nitric  acid,  with  deposition  of  metallic  gold.  Its 
solution  gives  a  blackish  precipitate  Avith  hydrosulphuric  acid 
and  soluble  sulphides.  The  presence  of  gold  in  this  solution 
is  not  indicated  by  protosulphate  of  iron,  protochloride  of  tin, 
or  oxalic  acid ;  and,  on  the  other  hand,  sulphuric  acid,  hydro- 
chloric acid,  and  the  vegetable  acids  neither  precipitate  sulphur 
nor  expel  sulphurous  acid  from  it.  When  mixed  with  chloride 
of  barium,  it  yields  a  gelatinous  precipitate  of  Hyposulphite  of 

aurous  oxide  and  baryta,  containing  o  g^Q  |  ^8202-     Sulphuric 

acid  removes  all  the  baryta  from  this  salt,  and  leaves  hydrated 
aurous  hyposulphite^  which  is  uncrystallisable,  strongly  acid, 
and  tolerably  stable  at  ordinary  temperatures.  The  solution 
of  the  soda-salt  is  used  for  fixing  daguerreotype  pictures 
(Fordos  and  Gelis).* 

A  hyposulphite  of  auric  oxide  and  soda  appears  also  to  be 
formed  by  dropping  a  neutral  solution  of  chloride  of  gold  into 
aqueous  hyposulphite  of  soda  (Fordos  and  Gelis). 

Alloys  of  gold.  —  Gold  unites  with  nearly  all  metals ;  but 
its  most  important  alloys  are  those  which  it  forms  with  silver 
and  copper.  Gold  which  is  used  for  coins,  watches,  articles 
of  jewellery,  &c.,  is  always  alloyed  with  copper,  to  increase  its 
nardness,  pure  gold  being  much  too  soft  for  any  of  these  pur- 
poses. The  standard  for  coin  in  the  United  Kingdom  is 
II  gold  with  I  alloy;  in  France  and  the  United  States  of 
America,  9  gold  to  1  alloy.  For  articles  of  jewellery,  gold  is 
also  frequently  alloyed  with  silver,  which  gives  it  a  lighter 
colour.  The  alloys  of  gold,  both  with  silver  and  with  copper, 
arc  more  fusible  than  gold  itself.     The  solder  used  for  gold 

*  Ann.  Ch  Phys.  [3],  xiii.  394. 


AURIC    COMPOUNDS.  359 

trinkets  is  composed  of  5  parts  gold  and  1  part  copper,  or 
of  4  parts  gold,  1  part  copper,  and  1  part  silver. 

Amalgam  of  gold.  —  Gold  unites  readily  with  mercury, 
forming  a  white  amalgam ;  the  smallest  quantity  of  mercurial 
vapour  coming  in  contact  with  gold  is  sufficient  to  turn  it 
white.  Mercury  is  capable  of  dissolving  a  large  quantity  of 
gold  without  losing  its  fluidity,  but,  when  quite  saturated,  it 
acquires  a  waxy  consistence.  When  the  liquid  amalgam  is 
strained  through  chamois-leather,  mercury  passes  through 
together  with  a  very  small  quantity  of  gold,  and  there  remains 
a  white  amalgam,  of  pasty  consistence,  containing  about 
2  parts  of  gold  to  1  part  of  mercury.  By  dissolving  1  part  of 
gold  in  1000  parts  of  mercury,  pressing  through  chamois- 
leather,  and  treating  the  residue  with  dilute  nitric  acid  at  a 
moderate  heat,  a  solid  amalgam,  AugHg,  is  obtained,  which 
crystallises  in  shining  four-sided  prisms,  retains  its  lustre  in 
the  air,  is  not  decomposed  by  boiling  nitric  acid,  and  does  not 
melt  even  when  heated  till  the  mercury  volatilises  (T.  H. 
Henry).* 

Gilding  and  silvering. — The  pasty  amalgam  of  2  parts  gold 
and  1  part  mercury  is  used  for  gilding  ornamental  articles  of 
copper  and  bronze.  The  surface  of  the  object  is  first  thoroughly 
cleaned  by  heating  it  to  redness,  then  plunging  it  into  dilute 
sulphuric  acid,  and  sometimes  for  an  instant  also  into  strong 
nitric  acid;  it  is  then  amalgamated  by  washing  it  with  a 
solution  of  nitrate  of  mercury,  and  afterwards  pressed  upon 
the  pasty  amalgam,  a  portion  of  which  adheres  to  it.  The 
mercury  is  then  expelled  by  heat,  and  the  gold-surface  finally 
polished.     Silver  may  be  gilt  by  similar  processes. 

By  substituting  an  amalgam  of  silver  for  the  amalgam  of 
gold,  articles  of  copper,  bronze,  and  brass  may  be  silvered  or 
plated. 

Articles  of  copper,  chiefly  copper  trinkets,  are  also  gilt  by 

*  Phil.  Mag.  [4],  ix.  468. 


360  GOLD. 

immersion  in  a  boiling  solution  of  chloride  of  gold  in  an  alka- 
line carbonate,  after  having  been  cleaned  by  processes  similar 
to  those  just  described. 

But  the  process  now  most  generally  adopted  is  that  of 
electro-gilding,  which  is  performed  by  immersing  the  objects 
to  be  gilt  in  a  solution  of  10  parts  of  cyanide  of  potassium 
and  1  part  of  cyanide  of  gold  in  100  parts  of  distilled  water, 
and  connecting  them  with  the  negative  pole  of  a  voltaic 
battery,  while  the  positive  pole  is  connected  with  a  bar  of 
gold  also  immersed  in  the  liquid.  The  solution  is  then  de- 
composed by  the  current,  the  gold  being  deposited  on  the 
objects  at  the  negative  pole,  while  the  gold  connected  with 
the  positive  pole  dissolves  and  keeps  the  solution  at  a 
nearly  uniform  strength.  The  cyanide  of  potassium  in  the 
solution  is  sometimes  replaced  by  ferrocyanide  of  potas- 
sium, and  the  cyanide  of  gold  by  sesquioxidc  of  gold, 
chloride  of  gold  and  potassium,  or  sidphide  of  gold ;  but  the 
composition  above  given  is  that  which  is  most  generally 
adopted.  This  mode  of  gUding  may  be  at  once  applied  to 
copper,  brass,  bronze,  silver,  or  platinum.  To  gild  iron,  steel, 
or  tin,  it  is  necessary  first  to  deposit  a  layer  of  copper  on  the 
surface,  which  is  effected  by  immersion  for  a  few  seconds  in  a 
bath  of  cyanide  of  copper  and  potassium. 

Electro-silvering  or  electro-plating  is  performed  in  a  similar 
manner,  with  a  bath  composed  of  1  part  of  cyanide  of  silver 
and  10  parts  of  cyanide  of  potassium  dissolved  in  100  parts 
of  water ;  it  is  principally  applied  to  articles  made  of  nickel- 
silver. 

Platinum  may  also  be  deposited  in  a  similar  manner  on 
copper  or  silver ;  but  it  does  not  adhere  very  firmly. 


ESTIMATION    OF    GOLD.  361 


ESTIMATION    OF    GOLD,   AND    METHODS    OF    SEPARATING    IT    FROM 
OTHER    METALS. 

Gold  is  always  estimated  in  tlie  metallic  state.  It  is  gene- 
rally precipitated  from  its  solution  in  aqua-regia  by  proto- 
sulpliate  of  iron  or  oxalic  acid.  Protosulphate  of  iron  pre- 
cipitates the  gold  in  the  form  of  a  fine  brown  powder.  K 
the  gold  solution  is  quite  neutral,  it  must  first  be  acidulated 
with  hydrochloric  acid,  otherwise  the  precipitated  gold  will 
be  contaminated  with  sesquioxide  of  iron  formed  by  the 
action  of  the  air  on  the  solution  of  the  protosulphate.  If  the 
gold  solution  contains  much  free  nitric  acid,  there  is  a  risk  of 
some  of  the  precipitated  gold  being  redissolved  by  the  aqua- 
regia  present.  To  prevent  this,  the  excess  of  nitric  acid  must 
be  destroyed  by  adding  hydrochloric  acid,  and  boiling  before 
the  iron  solution  is  added.  Oxalic  acid  reduces  gold  slowly 
but  completely ;  the  gold  solution  must  be  digested  with  it 
for  24  or  48  hours. 

These  methods  of  precipitation  serve  to  separate  gold  from 
most  other  metals.  In  such  cases,  oxalic  acid  is  mostly  to  be 
preferred  as  the  precipitating  agent,  because,  when  the  quan- 
tities of  the  other  metals  are  also  to  be  determined,  the 
presence  of  a  large  amount  of  iron  in  solution  is  very  incon- 
venient. 

The  separation  of  gold  in  alloys  may  generally  be  efiected 
by  dissolving  out  the  baser  metals  with  nitric,  or  sometimes 
with  hydrochloric  or  sulphuric  acid.  When,  however,  the 
proportion  of  gold  is  considerable,  it  may  happen  that  the 
alloy  is  but  very  slowly  attacked  by  nitric  acid,  especially  if 
the  other  metal  be  silver  or  lead.  In  such  a  case,  it  is  best 
to  treat  the  alloy  with  aqua-regia,  and  precipitate  the  gold 
with  oxalic  acid.  Or,  again,  the  alloy  may  be  fused  with  a 
known  weight  of  lead  or  silver,  as  in  the  method  of  quarta- 
tion  (p.  349.),  and  thereby  rendered  decomposable  by  nitric 
acid. 


362  GOLD. 

The  analysis  or  assay  of  an  alloy  of  gold  and  copper  is 
usually  made  by  cupcllation  with  lead.  The  weight  of  the 
button  remaining  on  the  cupel  gives  directly  the  amount  of 
gold  in  the  alloy  after  certain  corrections  similar  to  those 
required  in  the  case  of  silver  (p.  348.).  Alloys  containing 
both  silver  and  copper  are  cupelled  with  lead  and  a  quantity 
of  silver  sufficient  to  bring  the  proportion  of  gold  and  silver 
in  the  alloy  to  1  part  gold  and  3  parts  sUver.  The  button 
obtained  by  cupcllation  then  consists  of  an  alloy  of  gold  and 
silver,  from  which  the  silver  may  be  dissolved  out  by  nitric 
acid. 

Small  ornamental  articles,  which  would  be  destroyed  if 
submitted  to  any  of  the  preceding  processes,  are  approxi- 
mately assayed  by  rubbing  them  on  a  peculiar  kind  of  black 
stone,  called  the  touchstone^  so  as  to  leave  a  streak  of  metal, 
the  appearance  of  which  may  be  compared  with  that  of 
similar  streaks  produced  from  alloys  of  known  composition. 
A  further  comparison  is  obtained  by  examining  the  appear- 
ance which  the  streaks  present  when  treated  with  acids. 
This  method  is  also  sometimes  used  in  the  assaying  of  coins, 
to  afford  an  indication  of  the  quantity  of  silver  required  in 
the  cupcllation.  The  touchstone,  which  is  a  peculiar  kind 
of  bituminous  quartz,  was  originally  obtained  from  Lydia; 
but  stones  of  similar  quality  are  now  found  in  Bohemia, 
Saxony,  and  Silesia. 


PLATINUM.  363 


OEDEE   IX. 

METALS    IN    NATIVE    PLATINUM. 

SECTION    I. 

PLATINUM. 

Eq.  98-68  or  1233-5 ;  Pt. 

This  metal  was  discovered  in  the  auriferous  sand  of  certain 
rivers  in  America.  Its  name  is  a  diminutive  of  plata,  silver, 
and  was  applied  to  it  on  account  of  its  whiteness.  It  occurs 
in  the  form  of  rounded  or  flattened  grains  of  a  metallic  lustre. 
It  has  been  found  in  Brazil,  Colombia,  Mexico,  St.  Domingo, 
and  on  the  eastern  declivity  of  the  Ural  chain;  in  small 
quantity  also  in  certain  copper-ores  from  the  Alps;  it  is 
everywhere  associated  with  the  debris  of  a  rock,  easily  recog- 
nised as  belonging  to  one  of  the  earliest  volcanic  formations. 

The  grains  of  native  platinum  contain  from  75  to  87  per 
cent,  of  that  metal,  a  quantity  of  iron  generally  sufficient  to 
render  them  magnetic,  from  J  to  1  per  cent,  of  palladium,  but 
sometimes  much  less,  with  small  quantities  of  copper,  rhodium, 
osmium,  iridium,  and  ruthenium.  To  separate  the  platinum 
from  these  bodies,  the  ore  is  digested  in  a  retort  with  hydro- 
chloric acid,  to  which  additions  of  nitric  acid  are  made  from 
time  to  time.  When  the  hydrochloric  acid  is  nearly  saturated, 
the  liquid  is  evaporated  in  the  retort  to  a  syrup,  then  diluted 
with  water,  and  drawn  off"  from  the  insoluble  residue.  If  the 
mineral  is  not  completely  decomposed,  more  aqua-regia  is 
added  and  the  distillation  continued.  A  portion  always 
remains  undissolved,  consisting  of  grains  of  a  compound  of 

VOL.  II.  c  c 


364  PLATINUM. 

osmium  and  iridium^  and  little  brilliant  plates  of  the  same 
alloy,  besides  foreign  mineral  substances  which  may  be  mixed 
with  the  ore.  The  solution  is  generally  deep  red,  and  emits 
chlorine  from  the  presence  of  perchloride  of  palladium;  to 
decompose  which  the  liquid  is  boiled,  whereupon  chlorine 
escapes,  and  the  palladium  is  reduced  to  protochloride. 
Chloride  of  potassium  is  then  added,  which  precipitates  the 
platinum  as  a  sparingly  soluble  double  chloride  of  platinum 
and  potassium,  wliich  has  a  yellow  colour  if  pure,  but  red  if 
it  is  accompanied  by  the  double  chloride  of  iridium  and 
potassium.  The  precipitate  is  collected  on  a  filter,  and  washed 
^\dth  a  dilute  solution  of  chloride  of  potassium.  By  igniting 
this  double  salt  with  twice  its  weight  of  carbonate  of  potash 
to  the  point  of  fusion,  the  platinum  is  reduced  to  the  metallic 
state,  while  a  portion  of  the  iridium  remains  as  peroxide. 
The  soluble  potash-salts  are  then  removed  by  washing  with 
hot  water,  and  the  platinum  is  dissolved  by  aqua-regia,  in 
which  the  peroxide  of  iridium  remains  untouched.  To  com- 
plete the  separation  of  the  iridium,  the  precipitation  by 
chloride  of  potassium  and  ignition  vnth  carbonate  of  potash 
may  require  to  be  repeated  several  times.  The  platinum- 
solution  thus  freed  from  iridium  is  mixed  with  sal-ammoniac, 
which  throws  down  a  yellow  precipitate  of  the  double  chloride 
of  platinum  and  ammonium.  From  this  precipitate,  when 
heated  to  redness,  chlorine  and  sal-ammoniac  are  given  oflP, 
and  the  platinum  remains  in  the  form  of  a  loosely  coherent 
mass,  called  sjjongy  plathmm.  When  it  is  not  required  to 
have  platinum  absolutely  pure,  the  solution  first  obtained 
from  the  ore  is  precipitated  by  sal-ammoniac,  and  the  pre- 
cipitate treated  in  the  manner  just  described :  much  of  the 
platinum  of  commerce  is  obtained  in  that  way.  The  small 
trace  of  iridium  which  is  left  in  commercial  platinum  greatly 
increases  its  hardness  and  tenacity. 

Platinum  is  too  refractory  to  be  fused  in  coal  furnaces  :  but 
at  a  high  temperature  its  particles  cohere  like  those  of  ii'on. 


PLATINUM. 


365 


Fig.  19. 


and  it  may,  like  that  metal,  be  welded,  and  thereby  rendered 
malleable.  For  this  purpose,  the  spongy  platinum  obtained 
by  igniting  the  double  chloride  of  platinum  and 
ammonium,  is  introduced  into  a  brass  cylinder 
efg  h  {Fig.  20),  the  lower  part  of  which  fits  into  a 
steel  socket  abed.  The  cylinder  being  half  filled 
with  spongy  platinum,  a  steel  piston  ik,  which 
fits  it  exactly,  is  introduced,  and  driven  down  by 
blows  of  a  hammer,  gently  at  first,  but  afterwards 
with  greater  force.  The  spongy  platinum  is 
thereby  much  reduced  in  bulk,  and  after  a  while 
is  converted  into  a  coherent  disc  of  metal.  This 
disc  is  heated  to  whiteness  in  a  muffle,  and  after- 
wards hammered  on  a  steel  anvil.  By  repeating 
these  operations  several  times,  the  platinum  is 
rendered  perfectly  malleable  and  ductile,  and  may 
be  rolled  into  sheets.  Platinum  in  this  state  is 
the  densest  body  at  present  known ;  its  specific  gravity  was 
fixed  by  Dr.  WoUaston  at  21*53.  This  metal  may  be  fused 
by  the  oxyhydrogen  blow-pipe,  or  even  made  to  boil,  and 
be  dissipated  with  scintillations.  It  is  not  acted  upon  by 
any  single  acid,  not  even  by  concentrated  and  boiling  sul- 
phuric acid.  Its  resistance  to  the  action  of  acids,  conjoined 
with  its  difficult  fusibility,  renders  platinum  invaluable 
for  chemical  experiments,  and  for  some  purposes  in  the 
chemical  arts,  particularly  for  the  concentration  of  oil  of 
vitriol. 

The  remarkable  influence  of  a  clean  surface  of  platinum  in 
determining  the  combustion  of  oxygen  and  hydrogen,  has 
already  been  considered.  This  property  platinum  shares  with 
osmium,  iridium,  palladium,  and  rhodium.  It  is  exhibited  in 
the  greatest  degree  by  the  highly  divided  metal,  such  as  pla- 
tinum-sponge, the  condition  in  which  the  metal  is  left  on 
igniting  the  double  chloride  of  platinum  and  ammonium. 
Platinum  precipitated  from  solution  by  zinc,  causes  the  com- 

c  c  2 


366 


PLATINUM. 


bustion  of  alcohol  vapour.  The  black  powder  of  platinum, 
commonly  called  platinum-black,  is  the  form  in  which  that 
metal  is  most  active.  This  is  prepared  by  dissolving  the  pro- 
tochloride  of  platinum  in  a  hot  and  concentrated  solution  of 
potash,  and  pouring  alcohol  into  it  while  still  hot,  by  small 
quantities  at  a  time ;  violent  effervescence  then  occurs  from 
the  escape  of  carbonic  acid  gas,  by  which  the  contents  of  the 
vessel,  unless  capacious,  may  be  thrown  out.  The  liquor  is 
decanted  from  the  black  powder  which  appears,  and  the  latter 
boiled  successively  with  alcohol,  hydrochloric  acid,  and  potash, 
and  finally  four  or  five  times  with  water,  to  divest  it  of  all 
foreign  matters.  Platinum-black  may  also  be  obtained  by 
decomposing  a  hot  solution  of  sulphate  of  platinum  with 
alcohol ;  and  by  boiling  a  solution  of  the  bichloride  with  car- 
bonate of  soda  and  sugar ;  chloride  of  sodium  is  then  formed, 
water  and  carbonic  acid  are  produced  by  oxidation  of  the 
sugar,  and  the  platinum  is  precipitated  in  the  finely-divided 
state.  The  powder,  when  dried,  resembles  lamp-black,  and 
soils  the  fingers,  but  still  it  is  only  metallic  platinum  ex- 
tremely divided,  and  may  be  heated  to  full  redness  without 
any  change  of  appearance  or  properties.  It  loses  these  pro- 
perties, however,  by  the  effect  of  a  white  heat,  and  assumes  a 
metallic  aspect.  Platinum-black,  like  wood  charcoal,  absorbs 
and  condenses  gases  in  its  pores,  with  evolution  of  heat,  a 
property  which  must  assist  its  action  on  oxygen  and  hydrogen, 
although  not  essential  to  that  action.  When  moistened  with 
alcohol,  it  determines  the  oxidation  of  that  substance  in  air, 
and  the  formation  of  acetic  acid ;  and,  in  a  similar  manner, 
it  converts  wood-spirit  into  formic  acid. 

Platinum  is  insoluble  in  all  acids  except  aqua-regia.  It 
may  be  oxidated  in  the  dry  way  by  fusing  it  with  hydrate  of 
potash  or  nitre.  Palladium,  osmium,  and  iridium  resemble 
platinum  in  their  chemical  relations,  the  corresponding  com- 
pounds of  these  four  metals  being  isomorphous;  platinum 
and  iridium  have  also  the  same  atomic  weight.     Of  platinum. 


PLATINOUS    COMPOUNDS.  369^ 

only  two  degrees  of  oxidation  are  known  witn  certainty,  the 
protoxide,  PtO,  and  binoxide,  Pt02. 

Protoxide  of  platinum,  Platinous  oxide,  PtO,  106*68  or 
1333-5. —  This  oxide  is  obtained  by  digesting  the  corres- 
ponding chloride  of  platinum  with  potash,  as  a  black  powder, 
which  is  a  hydrate.  It  is  dissolved  by  an  excess  of  the  alkali, 
and  forms  a  green  solution,  which  may  become  black  like  ink 
with  a  large  quantity  of  oxide.  Protoxide  of  platinum  forms 
the  platinous  class  of  salts,  which  have  a  greenish,  or,  some- 
times red  colour,  and  are  distinguished  from  the  platinic  salts 
by  not  being  precipitated  by  sal-ammoniac.  With  hydrosuU 
phuric  acid  and  hydrosulphate  of  ammonia,  they  form  a  black 
precipitate,  soluble  in  a  large  excess  of  the  latter ;  with  mer- 
curous  nitrate,  a  black  precipitate;  with  potash,  no  precipitate; 
with  carbonate  of  potash  or  soda,  a  brownish  precipitate.  Am- 
monia added  to  the  hydrochloric  acid  solution  throws  down  a 
green  crystalline  precipitate  of  ammonio-platinous  chloride ; 
carbonate  of  ammonia  forms  no  precipitate. 

Protosulphide  of  platinum,  PtS,  is  thrown  down  as  a  black 
precipitate,  when  the  protochloride  of  platinum  is  decomposed 
by  hydrosulphuric  acid.  It.  may  be  washed  and  dried  without 
decomposition. 

Protochloride  of  platinum,  Platinous  chloride,  PtCl,  is  ob- 
tained by  evaporating  a  solution  of  the  bichloride  of  platinum 
to  dryness;  triturating  the  dry  mass;  and  heating  it  in  a 
porcelain  capsule  by  a  sand-bath  at  the  melting  point  of  tin, 
taking  care  to  stir  it  at  the  same  time,  so  long  as  chlorine  is 
evolved.  It  remains  as  a  greenish  grey  powder,  quite  insoluble 
in  water,  and  repelling  that  liquid  so  as  not  to  be  moistened 
by  it.  This  chloride  is  not  decomposed  by  sulphuric  or  nitric 
acid,  but  is  partially  soluble  in  boiling  and  concentrated  hy- 
drochloric acid.  From  the  last  solution,  alkalies  throw  down 
a  black  precipitate  of  protoxide.  When  the  calcination  of  the 
bichloride  of  platinum,  at  420°  or  460"^,  is  interrupted  before 
the  whole  of  the  chlorine  is  expelled,  the  residue  yields  to 

c  c  3 


368  PLATINUM. 

water  a  compound  of  a  bro^vn  colour,  so  deep,  that  the  liquid 
becomes  opaque.  This,  Professor  Magnus  believes  to  be  a 
combination  of  the  two  clilorides  of  platinum.  A  double 
protochloride  of  platinum  and  potassium^  or  chloroplaiinite  of 
potassium,  PtCl .  KCl,  is  obtained  on  adding  chloride  of 
potassium  to  the  solution  of  platinous  chloride  in  hydrochloric 
acid,  and  evaporating  the  liquid.  The  salt  crystallises  in  red 
four-sided  prisms,  the  form  of  which  is  the  same  as  that  of  a 
corresponding  salt  of  palladium  ;  it  is  anhydrous.  A  proto- 
chloride of  platinum  and  sodium  also  exists,  but  does  not 
crystallise  easily. 

Corresponding  platinous  iodides  and  cyanides  have  been 
formed.  The  cyanide  forms  a  numerous  class  of  double 
salts,  called  platinocyanides,  whose  general  formula  is 
MCy.PtCy.  The  potassium  salt  is  obtained  by  heating 
spongy  platinum  with  fcrrocyanide  of  potassium  ;  exhausting 
the  mass  with  hot  water  and  crystallising;  or  by  treating 
platinous  chloride  with  aqueous  cyanide  of  potassium.  The 
salt  crystallises  in  needles  and  rhombic  prisms,  pale  yeUow  by 
transmitted  light,  yellow  or  blue  by  reflected  light,  according 
to  the  direction  in  which  they  are.  viewed.  From  the  solution 
of  this  salt,  the  platino-cyanides  of  zinc,  lead,  copper,  mer- 
cury, and  silver,  which  are  insoluble,  are  obtained  by  precipi- 
tation. The  sodium,  barium,  strontium,  and  calcium-salts, 
which  are  soluble,  are  obtained  by  treating  the  copper-salt 
with  caustic  soda,  baryta,  &c. ;  and  the  magnesium  and 
aluminum- salts,  by  precipitating  the  barium-salt  with  sulphate 
of  magnesia  or  alumina.  The  ammonium-salt  is  prepared  like 
the  potassium-salt.  Platinous  oxide  has  also  been  united 
with  several  acids,  particularly  sulphuric,  nitric,  oxalic,  and 
acetic  acids ;  but  none  of  these  salts  have  been  crystallised, 
except  the  oxalate. 

Bioxide  of  platinum.  Peroxide  of  platinum,  Platinic  oxide, 
PtO.2,  111'68  07^  1433-5.  —  By  precipitating  sulphate  of  pla- 
tinum with  nitrate  of  baryta,  nitrate  of  platinum  is  obtained. 


PLATINIC    COMPOUNDS.  369 

One  half  of  its  oxide  may  be  precipitated  by  soda,  from  the 
last  salt,  but  when  a  larger  quantity  of  alkali  is  added,  a  sub- 
salt  is  thrown  down.  The  precipitated  oxide  is  hydrated, 
very  bulky,  and  exactly  resembles  sesquioxide  of  iron  precipi- 
tated by  ammonia.  When  heated,  it  first  loses  its  water,  and 
becomes  black,  then  its  oxygen,  and  leaves  metallic  platinum. 
Bioxide  of  platinum  combines  with  acids,  and  forms  a  class  of 
salts,  which  are  either  yellow  or  reddish-brown.  From,  the 
solutions  of  these  salts,  the  platinum  is  precipitated  in  the 
metallic  state  by  phosphorus  and  by  most  metals.  Hydrosul- 
phuric  acid  and  sulphide  of  ammonium  form  a  black  precipitate 
soluble  in  a  large  excess  of  the  latter.  In  a  solution  of  pla- 
tinic  chloride,  potash  or  ammonia  forms  a  yellow  crystalline 
precipitate  of  chloroplatinate  of  potassium  or  ammonium; 
so  likewise  do  the  chlorides  of  potassium  or  ammonium ; 
sodium-salts  form  no  precipitate.  In  the  solution  of  platinic 
nitrate  or  sulphate,  potash  or  ammonia  forms  a  yellow-brown 
precipitate ;  chloride  of  potassium  or  ammonium  produces, 
after  some  time,  a  slight  yellow  precipitate  of  the  double 
chloride.  Platinic  oxide  has  also  a  decided  affinity  for  bases, 
and  forms  insoluble  compounds  with  the  alkalies,  earths,  and 
many  metallic  oxides.  It  forms  also,  like  sesquioxide  of  gold, 
a  fulminating  ammoniacal  compound,  discovered  by  Mr.  E. 
Davy. 

Bisulphide  of  platinum,  PtS2,  is  formed  by  adding  a  solution 
of  bichloride  of  platinum,  drop  by  drop,  to  a  solution  of  sul- 
phide of  potassium.  It  is  dark  brown  and  becomes  black  by 
desiccation.  When  dried  in  open  air,  a  portion  of  its  sulphur 
is  converted  into  sulphuric  acid,  by  absorption  of  oxygen, 
and  the  mass  becomes  strongly  acid. 

Bichloride  of  platinum,  PtCl2,  2121  or  169'68,  is  obtained 
by  concentrating  the  solution  of  platinum  in  aqua-regia,  as  a 
red  saline  mass,  which  becomes  brown  when  deprived  of  its 
water  of  crystallisation  by  heat.  The  solution  of  this  salt 
when  pure  has  an  intense  and  unmixed  yellow  colour,  the  red 

c  c  4 


370  PLATINUM. 

colour  whicli  it  usually  exhibits  being  due  to  iridium  or  to 
protocbloride  of  platinum.  Bichloride  of  platinum  is  soluble 
in  alcohol,  and  the  solution  is  used  to  separate  potash  and 
ammonia  in  analysis. 

Chloride  of  platinum  and  potassium,  Chloroplatinate  of 
potassium,  KCl .  PtCl2,  is  the  salt  which  falls  on  mixing 
chloride  of  platinum  with  chloride  of  potassium  or  any  other 
salt  of  potash.  The  crystalline  grains  of  which  it  is  composed 
are  regular  octohedrons.  This  salt  is  soluble  to  a  certain 
extent  in  water,  but  is  wholly  insoluble  in  alcohol.  It  is 
anhydrous.  A  very  intense  red-heat  is  required  for  its  com- 
plete decomposition.  Chloroplatinate  of  sodium,  NaCl .  PtClj 
+  6H0,  crystallises  in  beautiful  transparent  prisms  of  a 
bright  yellow  colour.  It  is  soluble  in  alcohol  as  well  as  in 
water.  When  a  solution  of  this  salt  in  alcohol  is  distilled  till 
only  one-fourth  of  the  liquid  remains,  the  solution  yields  by 
evaporation  a  salt  containing  the  elements  of  ether,  and  be- 
longing to  a  class  of  compounds  discovered  by  Professor 
Zeise,  and  known  as  the  etherised  salts  of  Zeise. 

Chloroplatinate  of  ammonium  resembles  the  double  salt  of 
potassium.  When  ignited,  it  leaves  metallic  platinum  in  the 
spongy  state.  Bonsdorflf  has  formed  a  large  class  of  com- 
pounds of  bichloride  of  platinum  with  the  alkaline,  earthy, 
and  metallic  chlorides,  in  all  of  which  the  salts  are  united  in 
single  equivalents.  The  bromides  and  iodides  of  platinum 
have  likewise  been  formed,  and  classes  of  double  salts  derived 
from  them.  Bioxide  of  platinum  has  also  been  combined 
with  acids ;  but  none  of  its  salts,  with  the  exception  of  the 
oxalate,  is  obtained  in  a  crystalline  state. 

Bicyanide  of  platinum,  or  platinic  cyanide,  does  not  appear 
to  exist  in  the  separate  state ;  but  it  forms  double  salts  with 
the  cyanides  of  potassium  and  ammonium ;  it  likewise  com- 
bines with  chloride  of  potassium,  forming  the  compound 
KCl .  PtCy^. 

The  sulphocyanides  of  platinum,  PtCySg,  and  Pt,  (CyS2)2.. 


PLATINUM    SALTS.  371 

likewise  form  two  series  of  double  salts,  viz.  the  platino- 
bisulphocyanides  or  sulphocyanoplatinites  =  MPt(CyS2)2^  oi' 
MCyS2  +  PtCyS2,  and  theplatino-tersulphocyanides  or  sulpho- 
cyanoplatinates  =  MPt (€782)3,  or  MCyS2  +  Pt (0782)2-  The 
potassium  salts  are  formed  b7  the  action  of  sulphoc7anide  of 
potassium  on  protochloride  and  bichloride  of  platinum  re- 
spectively. All  these  salts  are  strongly  coloured,  exhibiting 
all  shades  of  colour  from  light  yellow  to  deep  red.  They  are 
quickly  decomposed  by  heat  (G.  B.  Buckton).* 

AMMONIACAL    PLATINUM    SALTS. 

The  oxides,  chlorides,  sulphates,  &c.,  of  platinum  are  capable 
of  taking  up  the  elements  of  1  or  2  equivalents  of  ammonia, 
giving  rise  to  four  series  of  compounds,  whose  composition 
may  be  represented  by  the  following  general  formulae,  in 
which  the  symbols  R,  B'  denote  acid  elements  : 

1.  Ammonio-platinous  compounds,  or  protosalts  of  pi  at  am- 
monium, 

NH3PtR=NH^P?.R. 

2.  Biammonio-platinous  compounds,  or  protosalts  of  ammo- 
platammonium, 

N2H6PtB=NH3raj5t .  R. 

3.  Ammonio-platinic  compounds,  or  bisalts  of  platammo- 
nium, 

NH3Pt{„,&=NH;Ft.{„^g|,,_ 

4.  Biammonio-platinic  compounds,  or  bisalts  of  ammo- 
platammonium. 

The  third  and  fourth  classes  of  these  compounds  may  also 
be  regai^ded  as  protosalts  of  compound  ammoniums,  in  which 

*  Chem.  Soc.  Qu.  J.  rii.  22. 


372  PLATINUM. 

1  eq.  of  hydrogen  is  replaced  by  PtO  or  PtCl ;  for  example, 
the  bichloride  NH3PtCl2=NH^(PtCi)  .CI;  the  chloronitrate 
N2H6PtClN06=NH^(NHJPtCl .  NOg. 

1.  Ammonio-platinous  compounds,  or  Protosalts  of  Plat- 
ammonium.  —  These  compounds  are  formed  by  the  action  of 
heat  on  those  of  the  follo^ving  series,  half  the  ammonia  of 
the  latter  being  then  given  off.  They  are  for  the  most  part 
insoluble  in  water,  but  dissolve  in  ammonia,  reproducing 
the  biammoniacal  platinous  compounds  ;  they  detonate  when 
heated. 

Oxide,  NH3PtO=NH3Pt.O.— Obtained  by  heating  the 
hydrated  oxide  of  biammo-platammonium  to  230°.  It  is  a 
greyish  mass  which,  when  heated  to  392°  in  a  close  vessel, 
gives  off  water,  ammonia,  and  nitrogen,  and  leaves  metallic 
platinum.  Probably  the  compound,  Pt3N,  is  first  produced 
and  is  afterwards  resolved  into  nitrogen  and  platinum  : 

3NH3PtO=Pt3N  +  3H0  +  2NH3. 

The  oxide,  heated  to  392°  in  contact  with  the  air,  becomes 
incandescent,  and  burns  vividly,  leaving  a  residue  of  platinum. 

Chloride,  NHaPtCl  =  NHgPt .  CI.  —  Of  this  compound 
three  isomeric  modifications  exist :  a.  Yelloiv,  obtained  by 
adding  hydrochloric  acid,  or  a  soluble  chloride,  to  a  solu- 
tion of  nitrate  or  sulphate  of  platammonium.  Or,  by  boiliug 
the  green  modification,  y,  with  nitrate  or  sulphate  of  am- 
monia, whereupon  it  dissolves  and  forms  a  solution  which,  on 
cooling,  deposits  the  yellow  salt.  Or,  by  neutralising  a  solu- 
tion of  platinous  chloride  in  hydrochloric  acid  with  carbonate 
of  ammonia,  heating  the  mixture  to  the  boiling  point,  and 
adding  a  quantity  of  ammonia  equal  to  that  already  contained 
in  the  liquid,  filtering  from  a  dingy  green  substance,  which 
deposits  after  a  while,  then  leaving  the  solution  to  cool,  and 
decanting  the  supernatant  liquid  as  soon  as  the  yellow  salt  is 


PLA.TINUM    SALTS.  373 

deposited.  /3.  Red. — If,  in  the  last  mode  of  preparation,  the 
carbonate  of  ammonia,  instead  of  being  added  at  once  in 
excess,  be  added  drop  by  drop  to  the  hydrochloric  acid  solu- 
tion of  platinous  chloride,  the  liquid  on  cooling  deposits  small 
garnet-coloured  crystals  having  the  form  of  six-sided  tables. 
This  red  modification  may  also  be  obtained  in  other  ways 
(Peyrone).*  y.  Green.  —  This  modification,  usually  denomi- 
nated the  green  salt  of  Magnus,  was  the  first  discovered  of 
the  ammoniacal  platinum  compounds.  It  is  obtained  by  gra- 
dually adding  an  acid  solution  of  platinous  chloride  to  caustic 
ammonia,  or  by  passing  sulphurous  acid  gas  into  a  boiling 
solution  of  bichloride  of  platinum  till  it  is  completely  con- 
verted into  protochloride  (and  therefore  no  longer  gives  a 
precipitate  with  sal-ammoniac),  and  neutralising  the  solution 
with  ammonia  ;  the  compound  is  then  deposited  in  green 
needles.  The  same  modification  of  the  salt  may  also  be  ob- 
tained by  adding  an  acid  solution  of  platinous  chloride  to  a 
solution  of  biammonio-platinous  chloride,  N2HgPtCl.  Hence 
it  would  appear  that  the  true  formula  of  this  green  salt  is 

(NH3PtCl)2=PtCl  +  NH^(NHJP"t .  CI,  that  of  the  yeUow  or 
red  modification  being  simply  NHaPtCl.  Either  modifica- 
tion of  the  salt,  when  heated  to  572°,  gives  off  nitrogen, 
hydrochloric  acid,  and  sal-ammoniac,  and  leaves  a  residue  of 
platinum. 

A  red  crystalline  compound  of  chloride  of  platammonium 
with  chloride  of  ammonium,  viz.  NHgPtCl  +  NH^Cl,  is  formed 
when  a  solution  of  chloride  of  ammo-platammonium,  contain- 
ing a  large  quantity  of  sal-ammoniac,  is  evaporated  to  the 
crystallising  point.  Thus,  when  a  solution  of  platinous  chlo- 
ride in  hydrochloric  acid  is  precipitated  by  ammonia,  and  the 
green  salt  of  Magnus  thereby  formed  is  heated,  while  still  in 
the  liquid,  with  excess  of  ammonia,  to  convert  it  into  chloride 
of  ammo-platammonium,  the  red  compound  separates  at  a 

*  Vide  Translation  of  Gmelin's  Handbook,  vi.  303. 


374  PLATINUM. 

certain  degree  of  concentration^  together  with  tlie  chloride  of 
ammo-plataramonium  (Grimm).* 

Iodide  J  NHaPtl.  —  Yellow  powder,  obtained  by  boiling  the 
aqueous  solution  of  the  compound  N2H6PtI.  It  dissolves  in 
ammonia,  and  is  thereby  reconverted  into  the  latter  com- 
pound. 

Cyanide,  NHgPtCy.  —  Obtained  by  adding  hydrocyanic 
acid  to  a  solution  of  biammonio-platinous  oxide,  cyanide  of 
ammoniimi  being  formed  at  the  same  time  (Reiset)  : 

NaHgPtO  +  2HCy = NHgPtCy  +  NH^Cy  +  HO. 

Also,  by  digesting  ammonio-platinous  chloride  with  cyanide  of 
silver.  It  crystallises  in  fine  regular  needles  of  a  pale  yellow 
colour,  soluble  with  tolerable  facility  in  water  and  ammonia. 
An  isomeric  modification  of  this  compound,  (NH3PtCy)2= 
N2H6PtCy  4-  PtCy,  is  formed  by  passing  cyanogen  gas  into  a 
moderately  concentrated  solution  of  biammonio-platinous 
oxide;  the  cyanogen  then  decomposes  the  water,  forming 
hydrocyanic  and  cyanic  acids,  and  the  hydrocyanic  acid  acts 
upon  the  biammonio-platinous  oxide,  forming  the  compound 
(NH3PtCy)2,  together  with  ammonia  and  water  : 

2  (N2H6PtO)  +  2HCy  =  (NH3PtCy)2  +  2NH3  +  2H0. 

The  compound,  (NH3PtCy)2,  crystallises  out  and  may  be 
purified  by  recry stall  isation  from  water.  It  is  also  obtained 
by  mixing  a  solution  of  biammonio-platinous  chloride  with 
cyanide  of  potassium.  It  forms  crystals  which,  under  the 
microscope,  appear  like  six-sided  tables  arranged  in  stellate 
groups ;  it  dissolves  without  decomposition  in  potash,  hydro- 
chloric acid,  and  dilute  sulphuric  acid,  but  is  decomposed  by 
strong  sulphuric  and  by  nitric  acids   (Buckton).t 

The  sulphate^^YL^Vi.^O^.TiO,  and  the  nitrate,  NHgPt.NOg, 
are  obtained  by  boihng  the  iodide  with  sulphate  and  nitrate 

*  Ann.  Ch.  Pharm.  xcix.  95. 
t  Chem.  Soc.  Qu.  J.,  iv.  34. 


AMMONIACAL    PLATINUM    SALTS.  375 

of  silver ;  they  are  crystalline,  and  have  a  strong  acid  reaction. 
The  sulphate  retains  one  atom  of  water,  which  cannot  be  re- 
moved without  decomposing  the  salt. 

2.  Biammonio-platindus  compounds,  or  Protosalts  of  Ammo- 

platammonium.— Oxide,  NaHgPtO  .  HO  =  NH2(NH4)Pt  .0  + 
HO. — Obtained  by  decomposing  the  solution  of  the  sulphate 
with  an  equivalent  quantity  of  baryta- water,  and  evaporating 
the  filtrate  in  vacuo;  a  crystalline  mass  is  then  left,  con- 
taining N2H6PtO  .  HO.  The  oxide  is  not  known  in  the  anhy- 
drous state.  The  hydrate  is  strongly  alkaline  and  caustic, 
like  potash,  absorbs  carbonic  acid  rapidly  from  the  air,  and 
precipitates  oxide  of  silver  from  the  solution  of  the  nitrate. 
It  is  a  strong  base,  neutralising  acids  completely,  and  ex- 
pelling ammonia  from  its  salts.  It  melts  at  230°,  giving  off 
water  and  ammonia,  and  leaving  the  compound  NH3PtO. 
Its  aqueous  solution  does  not  give  off  ammonia,  even  when 
boiled. 


Chloride,  N2H6PtCl  =  NH2(NH4)Pt .  CI.— This  compound 
is  prepared  by  boUing  protochloride  of  platinum,  or  the  green 
salt  of  Magnus,  with  aqueous  ammonia,  till  the  whole  is  dis- 
solved, and  evaporating  the  liquid  to  the  crystallising  point. 
Or,  by  passing  sulphurous  acid  gas  into  bichloride  of  platinum 
till  the  solution  is  completely  decolorised,  precipitating  with 
carbonate  of  soda,  dissolving  the  precipitate  of  sodio-platinous 
sulphite  in  hydrochloric  acid,  saturating  the  resulting  solution 
of  chloride  of  sodium  and  platinous  chloride  with  ammonia, 
and  dissolving  the  precipitate  of  N2H6PtCl  and  NHgPtCl 
in  boiling  hydrochloric  acid.  The  filtered  liquid  on  cooling 
deposits  NHgPtCl,  while  the  biammoniacal  compound  remains 
in  solution  and  may  be  obtained  by  evaporation,  mixed  how- 
ever, with  sal-ammoniac.  It  separates  in  bulky  crystals  of  a 
faint  yellow  colour,  containing  1  eq.  water,  which  is  com- 
pletely given  off  at  230°.  At  482°  it  gives  off  ammonia,  and 
leaves  NHaPtCl.     The  anhydrous  compound  rapidly  absorbs 


376  PLATINUM. 

water  from  the  air.  The  hydrate  does  not  give  off  ammonia 
when  treated  with  caustic  alkalies  in  the  cold,  and  is  but 
very  slowly  decomposed  by  them,  even  with  the  aid  of  heat. 

Chloride   of  ammo-platammonium   forms   two   compounds 
with  bichloride  of  platinum.      The  first,  whose  formula  is 


2(NH2  (NH^)  Pt.  CI)  +  PtClg,  is  obtained  as  an  olive-green 
precipitate  on  adding  bichloride  of  platinum  to  a  solution  of 

NH7(NHJPt .  CI ;  the  second,  Nh7(NH J  Pt .  CI  -f  PtCl^, 
by  treating  the  preceding  with  excess  of  bichloride  of  pla- 
tinum. 

The  bromide  and  iodide  of  this  series  are  obtained  by 
treating  the  solution  of  the  sulphate  with  bromide  or  iodide 

of  barium :  they  crystallise  in  cubes. 

X * . 

The    sulphate,    NH2  (NH^)  Pt  .  SO4,    and    the    nitrate, 

NH2(NH4)Pt.N06,  are  obtained  by  decomposing  the  chloride 
with  sulphate  or  nitrate  of  silver;  they  are  neutral,  and 
crystallise  easily. 

Carbonates.  —  The  hydrated  oxide  absorbs  carbonic  acid 
rapidly   from   the   air,   forming   first,    a  neutral   carbonate, 

NH2  (NH4)  Pt .  CO3  +  no,   and   afterwards   an   acid   salt, 

NH2(NH,)Pt.C03  +  CO3H. 

3.  AmmoniO'platinic  compounds;    or,   Bi-salts  of  platam- 

monium. — The  oxide,  l^Yi^iO<^=^VL.^t  .O^j  may  also  be 

regarded  as  oxide  of  oxy plat  ammonium,  NH3  (PtO)  .0.  It  is 
obtained  by  adding  ammonium  to  a  boiling  solution  of  am- 
monio-platinic  nitrate ;  it  is  then  precipitated  in  the  form  of 
a  heavy,  yellowish,  crystalline  powder,  composed  of  small, 
shining,  rhomboid al  prisms;  it  is  nearly  insoluble  in  boiling 
water,  and  resists  the  action  of  boiling  potash.  Heated  in  a 
close  vessel,  it  gives  off  water  and  ammonia,  and  leaves  metallic 
platinum.     It  dissolves  readily  in  dilute  acids,  even  in  acetic 


AMMONIACAL    PLATINUM    SALTS.  377 

acid,  and  forms  a  large  number  of  crystallisable  salts,  both 
neutral  and  acid,  having  a  yellow  colour,  and  sparingly  soluble 
in  water  (Gerhardt).*  Another  compound  of  platinic  oxide 
with  ammonia,  called  fulminating  platinum,  whose  compo- 
sition has  not  been  exactly  ascertained,  is  produced  by  de- 
composing chloroplatinate  of  ammonium  with  aqueous  potash. 
It  is  a  straw-coloured  powder  which  detonates  slightly  when 
suddenly  heated,  but  strongly  when  exposed  to  a  gradually 
increasing  heat. 

Chloride,  NH3PtCl2  =  NH^.  CI2  =  NH3  (PtCl) .  CI.  — 
Obtained  by  passing  chlorine  gas  into  boiling  water  in  which 
the  compound  NHgPtCl  (the  yellow  modification)  is  sus- 
pended. This  compound  is  insoluble  in  cold  water,  and  very 
slightly  soluble  in  boiling  water,  or  in  water  containing  hy- 
drochloric acid.  It  dissolves  in  ammonia  at  a  boiling  heat, 
and  the  solution,  on  cooling,  deposits  a  yellow  precipitate, 
consisting  of  biammoniacal  platinic  chloride.  The  compound 
NHgPt .  CI2  dissolves  in  boiling  potash  without  evolving  am- 
monia.    An  isomeric  compound, 

(NHaPtCl,),  =  N^HePtCl,  +  PtCl^ 

is  obtained  by  passing  chlorine  into  water  in  which  Magnuses 
green  salt  is  suspended.  A  red  crystalline  powder  is  at  first 
precipitated,  consisting  of  N2HgPtCl  +  PtCl2;  but  on  con- 
tinuing the  passage  of  the  chlorine,  this  precipitate  redis- 
solves,  and  the  solution  yields,  by  evaporation,  the  crystalline 
compound  (NH3PtCl2)2- 

The  sulphate,  NHgPt .  (804)3,  ^^  obtained  by  dissolving  the 
oxide  in  dilute  sulphuric  acid,  and  evaporating.  It  is  a  yellow 
powder,  having  an  acid  taste,  and  is  soluble  in  boiling  water. 

Nitrates.  —  A  mononitrate,  NH3Pt02  .  NO5  +  3H0,  or 
oxynitrate,  NH3Pt .  |     q^  +  3H0,  or  nitrate  of  oxyplat- 

*  Comptes  Eendus  des  Traraux  de  Chimie,  1849,  p.  273. 


378  PLATINUM. 

ammonium^  NH3  (PtO) .  NOg  +  3H0,  is  obtained  by  boiling 
the  chloride  NH3PtCl2  for  several  hours  with  a  dilute  solution 
of  nitrate  of  silver.  It  is  a  yellow,  crystalline  powder,  spar- 
ingly soluble  in  cold,  more  soluble  in  boiling  water.     The 


binitrate,  NHgPt .  2N06  +  2H0,  is  obtained  by  dissolving 
the  mononitrate  in  nitric  acid :  it  is  yellowish,  insoluble  in 
cold  water,  soluble  in  hot  nitric  acid. 

The  oxalate,  ^"H^ViO^.C^O^  +  2H0,  or  NHgPtI  ^2^4  ^ 

2H0,  or  NH3  (PtO).  C20^  +  2H0,  is  formed  by  decomposing 
the  nitrate  with  oxalate  of  ammonia.  It  is  a  light  yellow 
precipitate,  soluble  in  boiling  water,  and  detonating  when 
heated. 

4.  BiammoniO'platinic  compounds,  or  Bi-salts  of  ammo- 
plat  ammonium.  —  The  oxide  of  this  series  has  not  yet  been 
isolated. 


Chloride. —-^^  HePtCl^  =   N  H^IN  HJ  Pt .  CI2  = 

NH2  (NH  J  (PtCl)  .  CI.  —  Obtained  by  passing  chlorine  gas 
into  a  solution  of  biammonio-platinous  chloride,  N2H6PtCl; 
by  dissolving  ammonio-platinic  chloride,  NH3PtCl2,  in  am- 
monia, and  expelling  the  excess  of  ammonia  by  evaporation ; 
or  by  precipitating  a  solution  of  one  of  the  nitrates, 

N2HgPt02 .  NO5,  or  N2H6PtC10 .  NO5, 

with  hydrochloric  acid.  It  is  white,  and  dissolves  in  small 
quantity  in  boiling  water,  jfrom  which  solution  it  is  deposited 
in  the  form  of  transparent,  regular  octohedrons,  having  a 
faint  yellow  tint.  When  a  solution  of  this  salt  is  treated 
with  nitrate  of  silver,  one  half  of  the  chlorine  is  very  easily 
precipitated,  but  to  remove  even  a  small  portion  of  the  re- 
mainder requires  a  long -continued  action  of  the  silver-salt; 
a  result  easily  explained  if  the  salt  be  regarded  as  a  chlo- 


AMMONIACAL    PLATINUM    SALTS.  379 

ride  of  ammo-chlorplatammonium,  NH2  (NHJ  (PtCl)  .  CI 
(Grimm.)*  A  compound  having  the  formula  N2H5PtCl, 
containing,  therefore,  1  eq.  CI  and  1  eq.  H  less  than  the  pre- 
ceding, is  obtained  by  dissolving  chloroplatinate  of  ammonium 
in  ammonia,  and  precipitating  by  alcohol;  but  it  does  not 
crystallise,  merely  drying  up  to  a  pale  yellow,  resinous  mass : 
hence  its  composition  is  doubtful. 

Nitrates. — A  mononitrate,  N2HgPt02.N05,or  oxynitrateof 

ammoplatammonium,NH2(NH4)Pt|     q^  or  nitrate  of  am- 

moxyplatammonium,  NH2  (NH4)  (PtO)  .  NOg,  is  obtained  by 
boiling  the  following  salt  5,  with  ammonia :  it  is  a  white 
amorphous  powder,  slightly  soluble  in  cold,  more  soluble  in 
boiling  water. 

Sesquinitrate,  2(N2H6Pt02)  .SNOg,  or 

2('NH2(NH,)PtY     "^^^^  or      , .^-.  pNOg.- 

V  /    i       ^        NH2(NHJ(PtN06)J 

Formed  by  boiling  the  mononitrate  of  ammoplat ammonium 
with  nitric  acid.     It  is  a  colourless,  crystalline,  detonating 
salt,  slightly  soluble  in  cold  water,   more  soluble  in  boiling 
water,  insoluble  in  nitric  acid  (Gerhardt). 
Chloronitrates.—a.  NaHfiPtClO  .NO.;  or 

NH^^NEgPt .  {  "^ci'  «^  NH^(NlSj^Pta) .  NOg.  —  This  salt 
was  discovered  by  Gros.  It  is  obtained  by  treating  Magnuses 
green  salt  with  strong  nitric  acid.  The  green  compound  first 
turns  brown,  and  is  afterwards  converted  into  a  mixture  of 
platinum  and  a  white  powder,  which  is  dissolved  out  by  boil- 
ing water,  and  crystallises  on  cooling  in  shining  flattened 
prisms,  colourless,  or  having  a  pale  yellow  tint.  The  reaction 
may  be  thus  represented  :  — 

2(NH3PtCl)  +  HO  .  N05=N2H6PtCl .  NOg  f  I*t-f  HCl. 

*  Ann.  Cli.  Pharm.  xcix.  77. 
VOL.  TI.  D  D 


380  PLATINUM. 

This  compound  dissolves  readily  in  water,  especially  T\'hcn 
heated.  The  chlorine  and  platinum  contained  in  the  solution 
cannot  be  detected  by  the  ordinary  reagents ;  thus,  nitrate  of 
silver  and  hydrosulphuric  acid  yield  but  very  trifling  precipi- 
tates, even  after  a  long  time. 

b,  4NH3  .  PtaClOa  .  2NO5,  or  ^IWH4)(PtCl)  |     gNOg. 

NH2(NHJ(PtCl)) 

Discovered  by  Raewsky.  When  Magnus's  green  salt  is  boiled 
with  a  large  excess  of  nitric  acid,  red  fumes  are  evolved,  and 
the  resulting  solution  deposits  this  salt  in  small,  brilliant, 
needle-shaped  prisms,  which  deflagrate  when  heated,  giving 
off  water  and  chloride  of  ammonium,  and  leaving  metallic 
platinum.  Raewsky  assigns  to  this  salt  the  formula 
4NH3  .  PtjClOg  .  2NO5 ;  but  the  formula  above  given,  which 
is  deduced  from  Gerhardt's  analysis,  and  contains  20  less, 
is  much  more  probable,  as  it  accords  with  the  constitution  of 
the  other  compounds  of  the  series.  The  2  atoms  of  nitric 
acid  contained  in  this  salt  may  be  replaced  by  2  atoms  of 
carbonic  or  oxalic  acid,  yielding  sparingly  soluble  ci-ystalline 
salts  of  exactly  similar  constitution.  There  is  also  a  phos- 
phate containing  iNH,  .  Pt2C103  .  PO5  .  HO,  o])tained  by 
mixing  the  solution  of  the  nitrate  with  ordinary  phosphate  of 
soda.  According  to  Raewsky,  the  mother-liquor  from  which 
the  preceding  nitrate  has  crystallised,  contains  another  nitrate 
whose  formula  is  4NH3.Pt2Cl2O4.2NO5;  but  Gerhardt 
finds  this  salt  to  be  identical  with  the  nitrate  discovered  by 
Gros. 

Chlorosulphate,  N2H6PtClS04=NH^(NlSj^Ptci)  .  SO^.— 
Obtained  by  treating  biammonio-platinic  chloride,  or  Gros's 
nitrate,  with  dilute  sulphuric  acid,  or  by  mixing  the  solution 
of  the  nitrate  with  a  strong  solution  of  a  soluble  sulphate.  It 
crystallises  in  slender  needles,  sparingly  soluble  in  cold  water, 
but  dissohdng  with  tolerable  facility  in  boiling  water.     The 


AMMONIACAL    PLATINUM    SALTS.  381 

sulphuric  acid  in  the  solution  is  not  precipitated  by  baryta- 
salts.  The  salt  is,  however,  decomposed  by  hydrochloric  or 
nitric  acid,  either  of  which  takes  the  place  of  the  sulphuric 
acid,  reproducing  the  chloride  or  nitrate  (Gros). 

Chloroxalate,  NaHgPtClO  .  C2O3  =  NH2(NH4)Pt  |    ^  cl  "^ 

NH2(NH4)(PtCl)  .  C2O4. — Oxalic  acid  or  an  alkaline  oxalate 
added  to  the  solution  of  the  corresponding  sulphate  or  nitrate, 
throws  down  this  salt  in  the  form  of  a  white  granular  pre- 
cipitate, insoluble  in  water. 

Oxalonitrates.  —  a.    N2HgPt02  .  NO5  .  C2O3  = 

NH^mjpt.  [c^\  =  nh^cnhIkpIno;)  .  c  A- 

Deposited  as  a  white  crystalline  body  from  a  solution  of 
the  following  salt  b  in  dilute  nitric  acid. 

b.  2(N2H6Pt02)  .  NO5 .  2C2O3  =  2(NH^(]NT^       .1    NO^  = 
^  ■       .  i       O 

NH2(Nh')  (PtNOg)  }  2C20,.-Obtained  by  adding  oxalate  of 
ammonia  to  a  solution  of  the  sesquinitrate ;  it  is  insoluble  in 
water  (Gerhardt). 

GERHARDt's    theory    of   the    AMMONIACAL   PLATINUM 
COMPOUNDS. 

These  compounds  may  be  regarded  as  salts  of  peculiar  bases 
or  alkalies,  formed  from  ammonia  by  the  substitution  of  one 
or  two  atoms  of  platinum  for  hydrogen ;  admitting,  however, 
that  platinum  (like  other  metals)  may  enter  into  its  com- 
pounds with  two  different  equivalent  weights,  viz.,  in  the 
platinow*  compounds,  as  Platinosum  =  98*68  =  Pt,  and  in  the 
platinic  compounds,  as  Platinicum  =  49*34  =  pt.  This  being- 
admitted,  the  ammonio-platinous  compounds  may  be  regarded 
as  salts  of  an  alkali,  called  Platosamine  =  NH2Pt,  formed 
from  ammonia  by  the  substitution  of  1  atom  of  platinosum  for 
1  atom  of  hydrogen ;  and  the  biammonio-platinous  compounds, 

D  D  2 


382  PLATINUM. 

as  salts  of  Diplatosamine  =  NgH^Pt,  formed  by  the  union  of 
two  atoms  of  ammonia  into  one,  and  the  substitution  therein 
of  1  Pt  for  IH  :  thus  for  the  chlorides  :  — 

NH3PtCl= Hydrochlorate  of  Platosamine  =  NH2Pt .  HCl ; 

N2H6PtCl=HydrochlorateofDiplatosamine=N2ll5Pt.HCl; 

and  for  the  nitrates : — 

NH3Pt.N06= Nitrate  of  Platosamine=NH2Pt .  HNOg; 

NsHgPt.NOgrr:  Nitrate  of  Diplatosamine =N2H5Pt .  HNOg. 

In  a  similar  manner,  the  ammonio-platinic  compounds 
may  be  regarded  as  salts  of  Platinamine  =  NHpt2,  and  the 
biammonio-platinic  compounds  as  salts  of  Diplatinamine  = 
N2H4pt2;  thus  — 

NHaPtClj  =  Bihydrochlorate  of  Platinamine  =  NHpt2  .  2HC1. 
N2ll6PtCl2 = Bihydrochlorate  of  Diplatinamine = N2H4pt2 .  2HC1. 

Diplatinamine  forms  three  kinds  of  salts,  viz.,  mono-acid, 
sesqui-acid,  and  bi-acid  salts ;  and,  moreover,  exhibits  a 
peculiar  tendency  to  form  double  salts  containing  two  acids  : 
thus,  the  salts  discovered  by  Gros  may  be  regarded  as  bi-acid 
salts,  and  those  discovered  by  Raewsky,  as  sesqui-acid  salts 
of  diplatinamine  containing  hydrochloric  together  with  another 
acidj  thus: — 

Mononitrate =N2H6Pt02 .  N05  =  N2H4pt2  .  HN06  +  HO. 

Sesquinitrate=2(N2H6Pt02) .  SNOg  =  2N2H4pt2 .  SHNOg  +  HO. 

fSSre)}  =N,H«PtC10.N0,  =  N,H,pt,.  |HC1^^ 

Oxalonitrate = N2H6Pt02 .  NO5 .  C2O3  =  N2H4pt2 .  |  ^^^q  * 
Sesqui-oxalonitrate  =  2(N2H6Pt02)  .  NO5  .  2C2O3  = 
2N2H,pt2.f^5g^  +  HO. 


ESTIMATION    OF   PLATINUM.  383 


ESTIMATION   AND    SEPARATION    OP   PLATINUM. 

For  quantitative  estimation,  platinum  is  usually  precipitated 
from  its  solutions  in  the  form  of  cMoroplatinate  of  ammonium. 
The  acid  solution  of  platinum,  after  sufficient  concentration, 
is  mixed  with  a  very  strong  solution  of  sal-ammoniac,  and  a 
sufficient  quantity  of  strong  alcohol  added  to  render  the  pre- 
cipitation complete.  The  precipitate  of  chloroplatinate  of 
ammonium  is  then  washed  with  alcohol,  to  which  a  small 
quantity  of  sal-ammoniac  has  been  added,  and  then  heated  to 
redness  in  a  weighed  porcelain  crucible,  whereupon  it  is  de- 
composed and  leaves  metallic  platinum.  Great  care  must, 
however,  be  taken  in  the  ignition  to  prevent  loss,  as  the 
evolved  vapours  are  very  apt  to  carry  away  small  particles  of 
the  salt  and  of  the  reduced  metal.  The  best  mode  of  avoiding 
this  source  of  error  is  to  place  the  precipitate  in  the  crucible 
enclosed  in  the  filter,  and  expose  it  for  some  time  to  a  moderate 
heat,  with  the  cover  on  the  crucible,  till  the  filter  is  charred, 
and  then  to  a  somewhat  higher  temperature  to  expel  the 
chlorine  and  chloride  of  ammonium.  The  crucible  is  then 
partially  opened  and  the  carbonaceous  matter  of  the  filter 
burnt  away  in  the  usual  manner.  When  these  precautions 
are  duly  observed,  not  a  particle  of  platinum  is  lost.  Instead 
of  igniting  the  precipitate  and  weighing  the  platinum,  the 
precipitate  is  sometimes  collected  on  a  weighed  filter,  dried 
over  the  water-bath  and  weighed ;  but  this  method  is  less 
accurate,  because  the  precipitate  always  contains  an  excess  of 
sal-ammoniac  (H.  Eose). 

Chloride  of  potassium  may  also  be  used  instead  of  chloride 
of  ammonium  to  precipitate  platinum,  the  concentrated  so- 
lution of  the  platinum  being  previously  mixed  with  a  sufficient 
quantity  of  strong  alcohol  to  bring  the  per  centage  of  alcohol 
in  the  liquid  to  between  60  and  70  per  cent.  The  precipitated 
chloroplatinate  of  potassium  is  then  washed  with  alcohol  of 

D  D    3 


384  PALLADIUxM. 

60  to  70  per  cent,  and  decomposed  by  simple  ignition  in  a 
porcelain  crucible,  if  its  quantity  is  small,  or  in  an  atmo- 
sphere of  hydrogen  if  its  quantity  is  larger ;  the  chloride  of 
potassium  washed  out  by  water;  and  the  platinum  dried, 
ignited,  and  weighed. 

Potash  and  ammonia  may  also  be  estimated  by  precipitat- 
ing their  solutions  with  chloride  of  platinum,  and  treating 
the  precipitates  in  the  manner  just  described.  Every  100 
parts  of  platinum  correspond  to  47*83  parts  of  potash,  and 
17*25  parts  of  ammonia. 

The  same  methods  of  precipitation  serve  also  for  the 
separation  of  platinum  from  most  of  the  preceding  metals. 
To  separate  platinum  from  silver,  when  tlie  two  metals  are 
combined  in  an  alloy,  the  best  method  is  to  heat  the  alloy 
with  pure  and  strong  sulphuric  acid,  diluted  with  about  half 
its  weight  of  water,  till  the  sulphuric  acid  begins  to  escape  in 
dense  fumes.  The  silver  is  thereby  converted  into  sulphate, 
and  the  platinum  remains  behind  in  the  metallic  state.  The 
sulphate  of  silver  is  dissolved  by  a  large  quantity  of  hot 
water,  the  platinimi  washed  with  hot  water,  and  again  treated 
with  sulphuric  acid,  to  separate  the  last  traces  of  silver. 


SECTION    II. 

PALLADIUM. 

^g.  53*36  or  665*9;    Pd. 

This  metal  was  discovered  in  1803  by  Dr.  Wollaston.  It 
is  precipitated  by  cyanide  of  mercury  from  the  solution  of 
the  ore  of  platinum,  after  the  removal  of  that  metal  by 
sal-ammoniac,  and  is  gradually  deposited  as  a  yellowish  white 
flocculent  powder,  which  is  cyanide  of  palladium,  and  yields 
the  metal  when  calcined.  Palladium  likewise  occurs,  asso- 
ciated with  a  larger  quantity  of  gold  and  a  small  quantity  of 


PROTOXIDE  OF  PALLADIUM.  385 

silver_,  in  a  peculiar  gold-ore  from  Brazil,  called  oropudre. 
This  mineral,  which  contains  10  per  cent,  of  palladium,  and 
is  the  chief  source  of  that  metal,  is  dissolved  in  aqua-regia, 
the  acid  solution  saturated  with  potash,  and  the  palladium 
precipitated  by  cyanide  of  mercury. 

In  external  characters,  palladium  closely  resembles  pla- 
tinum. It  is  nearly  as  infusible,  but  can  more  easily  be 
welded.  The  density  of  the  fused  metal  is  11-3  ;  after  being 
laminated,  11'8.  At  a  certain  temperature,  the  surface  of 
palladium  tarnishes  and  becomes  blue  from  oxidation,  but  at 
a  stronger  heat  the  oxide  is  reduced.  Palladium  is  very 
slightly  attacked  by  boiling  and  concentrated  hydrochloric 
and  sulphuric  acids.  It  dissolves  in  nitric  acid,  communi- 
cating a  brownish  red  colour  to  the  acid,  while  no  gas  is 
evolved  if  the  temperature  is  low,  the  nitric  acid  being  con- 
verted into  nitrous  acid.  Palladium  dissolves  with  facility  in 
aqua-regia;  its  surface  is  blackened  by  tincture  of  iodine, 
which  has  no  effect  upon  platinum. 

Palladium  is  sometimes  used  for  making  the  divided  scales 
of  astronomical  instruments ;  being  nearly  as  white  as  silver, 
and  not  blackened  by  sulphurous  emanations,  it  is  well 
adapted  for  that  purpose.  An  alloy  of  palladium  with 
I -10th  of  its  weight  of  silver  is  used  by  dentists. 

Palladium  has  a  much  greater  affinity  for  oxygen  than 
platinum.  It  forms  two  oxides,  the  protoxide  PdO,  and  the 
bioxide  Pd02. 

Protoxide  of  palladium,  Palladous  oxide,  PdO,  61 '27  or 
765*9. — This  oxide  is  obtained  by  dissolving  palladium  in 
nitric  acid,  evaporating  the  solution  to  dryness,  and  calcining 
the  nitrate  at  a  gentle  heat.  It  forms  a  black  mass,  which 
dissolves  with  difficulty  in  acids.  When  carbonate  of  potash 
or  soda  is  added  in  excess  to  a  palladous  salt,  the  hydrated 
protoxide  precipitates  of  a  very  dark  brown  colour.  This 
oxide  is  easily  deprived  of  its  water  by  heat,  but  a  violent 
calcination  is  necessary  to  reduce  it  to  the  metallic  state. 

D  D  4 


386  PALLADIUM. 

The  palladous  salts  are  for  the  most  part  brown  or  red ; 
their  taste  is  astringent,  but  not  metallic.  AVhen  ignited 
alone,  or  when  gently  heated  in  hydrogen  gas,  they  yield 
metallic  palladium.  The  metal  is  precipitated  from  the  solu- 
tions of  palladous  salts  by  phosphorus,  by  sulphurous  acid,  by 
nitrite  of  potash,  by  all  the  metals  which  reduce  silver,  by 
forrniate  of  potash,  and  by  alcohol  at  a  boUing  heat.  Hydro- 
sulphuric  acid  and  hydrosulphate  of  ammonia  throw  down  the 
brown  sulpliide  of  palladium,  insoluble  in  the  latter  reagent. 
Hydriodic  acid  and  iodide  of  potassium  throw  down  a  black 
precipitate  of  iodide  of  palladium,  visible  even  to  the 
500,000th  degree  of  dilution.  This  reaction  serves  for  the 
separation  of  iodine  from  bromine ;  for  alkaline  bromides  do 
not  precipitate  palladous  salts.  Potash  or  soda  forms  a  brown 
precipitate  of  a  basic  salt,  soluble,  with  the  aid  of  heat,  in 
excess  of  the  reagent.  Ammonia  produces  no  precipitate 
in  a  solution  of  palladous  nitrate;  but  from  a  solution  of 
the  chloride  it  throws  down  a  flesh-coloured  precipitate  of 
ammonio-chloride  of  palladium,  soluble  in  excess  of  ammonia. 
The  carbonates  of  potash  and  soda  form  a  brown  precipitate 
of  hydratcd  palladous  oxide.  Carbonate  of  ammonia  acts  like 
ammonia.  Phosphate  of  soda  forms  a  brown  precipitate. 
Ferroryanide  and  ferricyanide  of  potassium  form  no  preci- 
pitates, but  the  liquid  after  a  while  coagulates  into  a  jelly. 
Cyanide  of  mercury  throws  down  a  white  precipitate  of 
cyanide  of  palladium.  Protochloride  of  tin  forms  a  black 
precipitate,  which  dissolves  with  intense  green  colour  in 
hydrochloric  acid.  Protosulphate  of  iron  precipitates  palla- 
dium slowly  from  the  nitrate,  but  not  from  the  chloride. 
The  reactions  of  palladium  with  hydrosulphuric  acid,  cyanide 
of  mercury,  and  iodide  of  potassium  taken  together,  serve  to 
distinguish  it  from  all  other  metals. 

Protosulphide  of  palladium,  PdS,  is  obtained  by  precipi- 
tating a  palladous  salt  by  hydrosulphuric  acid,  and  is  of  a  dark 


PALLADOUS    COMPOUNDS.  387 

brown  colour ;  it  may  also  be  prepared  by  the  direct  union  of 
its  elements. 

Protochloride  of  palladium ,  PdCl^  is  prepared  by  dissolving 
palladium  in  hydrochloric  acid^  to  which  a  little  nitric  acid  is 
added,  and  evaporating  the  solution  to  dryness,  to  expel  the 
excess  of  acid.  The  compound  is  a  mass  of  a  dark  brown 
colour,  which  becomes  black  when  made  anhydrous  by  heat, 
and  may  be  fused  in  a  glass  vessel.  When  heated  in  platinum 
vessels,  it  becomes  contaminated  with  the  protochloride  of  that 
metal.  When  dissolved  with  chloride  of  potassium,  it  forms 
a  double  salt,  KCl .  PdCl,  which  is  soluble  in  cold,  and  consi- 
derably more  so  in  hot  water,  and  crystallises  in  fonr-sided 
prisms,  of  a  dull  yellow  colour.  Protochloride  of  palladium 
also  combines  with  chloride  of  ammonium  and  chloride  of 
sodium,  according  to  BonsdorfF,  and  forms  double  salts  with 
most  other  chlorides. 

Protocyanide  of  palladium,  PdCy,  is  always  formed  when 
cyanide  of  mercury  is  added  to  a  neutral  solution  of  palladium, 
as  a  light-coloured  precipitate,  which  becomes  grey  after  dry- 
ing. When  the  solution  of  palladium  is  acid,  no  precipitate 
is  formed,  and  when  the  solution  contains  copper,  the  preci- 
pitate has  a  green  colour.  Palladium  appears  to  have  a 
greater  affinity  for  cyanogen  than  any  other  metal.  Even 
cyanide  of  mercury  is  decomposed  when  boiled  with  protoxide 
of  palladium,  and  cyanide  of  palladium  formed.  When  this 
cyanide  is  dissolved  in  ammonia,  and  the  excess  of  the  latter 
allowed  to  escape  by  evaporation,  a  precipitate  of  brilliant, 
colourless,  crystalline  plates  is  formed,  which  appears  to  con- 
sist of  ammoniacal  cyanide  of  palladium. 

Nitrate  of  palladium,  PdO .  NO5,  is  formed  by  dissolving 
the  metal  in  nitric  acid  -,  the  solution  dries  up  into  a  dark  red 
saline  mass.  When  an  excess  of  ammonia  is  added  to  an 
acid  solution  of  this  salt,  and  the  solution  evaporated  by  a 
gentle  heat,  a  colourless  nitrate  of  palladium  and  ammonium 
is  deposited  in  rectangular  tables. 


388  PALLADIUM. 

Bioxide  of  palladium,  Peroxide  of  palladium,  Palladia  oxide, 
PdOj,  69-27  or  865*9. — To  prepare  this  oxide,  Berzelius  re- 
commends a  solution  of  the  liydrate  or  carbonate  of  potash 
to  be  added  by  small  quantities  at  a  time,  to  the  dry  bichloride 
of  palladium  and  potassium,  mixing  well  after  each  addition. 
A  yellowish  brown  powder  separates,  which  is  the  hydrated 
bioxide,  retaining  a  little  alkali.  Washed  with  boiling  water, 
it  loses  the  greater  part  of  its  combined  water  and  becomes 
black.  This  oxide  dissolves  with  difficulty  in  acids ;  the  solu- 
tions are  yellow.  The  corresponding  bisulphide  of  palladium 
has  not  been  formed. 

Bichloride  of  palladium,  Pd  CI2,  is  obtained  in  solution, 
when  the  protochloride  is  dissolved  in  concentrated  aqua- 
regia,  and  the  solution  only  slightly  heated.  Its  solution  is 
of  so  dark  a  brown  as  to  appear  black,  and  gives  a  red  preci- 
pitate with  chloride  of  potassium.  When  the  solution  is 
diluted  or  heated,  chlorine  gas  is  evolved,  and  protochloride 
of  palladium  reproduced.  The  double  salt  of  this  chloride 
and  chloride  of  potassium  is  obtained  by  treating  the  double 
protochloride  of  palladium  and  potassium  in  fine  powder  with 
aqua-rcgia,  and  evaporating  the  sujiernatant  fluid  to  dryness. 
It  forms  a  cinnabar  red  powder,  in  which  little  octohedral 
crystals  can  be  perceived,  both  the  palladic  and  palladous 
double  chlorides  being  isomorphous  with  the  corresponding 
compounds  of  platinum.  When  treated  Avith  hot  water,  this 
double  salt  emits  chlorine,  and  is  in  a  great  measure  decom- 
posed.    The  salts  of  bioxide  of  palladium  are  scarcely  known. 

Ammoniacal  compounds  of  palladium. — A  moderately  con- 
centrated solution  of  protochloride  of  palladium  treated  with 
a  slight  excess  of  ammonia,  yields  a  beautiful  flesh-coloured 
or  rose-coloured  precipitate,  consisting  of  NHgPdCl.  This 
precipitate  dissolves  in  a  larger  excess  of  ammonia;  and  the 
ammoniacal  solution,  when  treated  with  acids,  yields  a  yellow 
precipitate  having  the  same  composition.  This  yellow  modi- 
fication is  likewise  obtained  by  heating  the  red  compound  in 


AMMONIACAL    COMPOUNDS    OF    PALLADIUM.  389 

the  moist  state  to  212°,  or  in  the  dry  state  to  392°.  The 
yellow  compound  dissolves  abundantly  in  aqueous  potash, 
forming  a  yellow  solution,  but  without  giving  off  ammonia, 
even  when  the  liquid  is  heated  to  the  boiling  point ;  the  red 
compound  behaves  in  a  similar  manner,  but,  before,dissolving, 
is  converted  into  the  yellow  modification.  For  this  reason, 
Hugo  Miiller,  who  has  lately  made  the  ammoniacal  compounds 
of  palladium  the  subject  of  an  elaborate  examination,  regards 
the  red  compound  as  ammomo-palladous  chloride,  NHg.PdCl, 

and  the  yellow,  as  chloride  of  palladammonium,  NHgPd .  CI. 
The  yellow  compound,  digested  with  water  and  oxide  of  silver, 
yields  the  oa7ic?e  of palladammonium  {or  palladamine),'N}l^Vd.O. 
This  compound  is  a  strong  base,  analogous  to  oacide  of  plat- 
ammonium  (p.  374).  It  is  soluble  in  water,  to  which  it  com- 
municates a  strong  alkaline  taste  and  reaction ;  by  evaporating 
the  solution  in  vacuo,  the  base  is  obtained  in  the  form  of  a 
crystalline  mass,  which  absorbs  carbonic  acid  rapidly  from  the 
air,  especially  when  moist.  It  unites  with  acids,  forming 
definite  salts.  Its  solution  precipitates  the  salts  of  silver  and 
copper,  and  an  excess  of  it  does  not  redissolve  the  precipi- 

tates.  Sulphite  of  palladammonium,  NH3Pd .  SO3,  is  formed 
by  saturating  the  solution  of  the  oxide  with  sulphurous  acid, 
or  by  the  action  of  that  acid  on  the  yellow  chlorine-compound : 
it  crystallises  in  orange-yellow  octohedrons.     The  sulphate, 

NH3Pd .  SO4,  crystallises  in  a  similar  manner.  The  nitrate, 
iodide,  and  bromide  have  also  been  formed.  The  fluoride  is 
obtained  by  adding  the  chloride  to  a  solution  of  fluoride  of 
silver. 

Chloride  of  ammopalladammonium  (or  chloride  of  pallad^ 
diamine,  according  to  Miiller), 


2NH3  .  PdCl  =  NH2  (NliJ  Pd  .  CI, 

separates  from  the  ammoniacal  solution  of  chloride  of  pal- 
ladammonium, in  colourless,  oblique  rhombic  prisms,  which 


390  PALLADIUM. 

at  392°  give  off  half  tlieir  ammonia  and  are  reduced  to 
NHgPd .  CI.  The  iodide  and  bromide  of  ammopalladam- 
monium  are  likewise  obtained  by  treating  the  solutions  of 
iodide  and  bromide  of  palladium  or  palladammonium  with 
ammonia.  ^  They  both  crystallise  readily.  The  fluoride  is 
obtained  by  adding  ammonia  to  the  solution  of  chloride  of 
palladammonium  in  fluoride  of  silver,  and  evaporating :  it 
forms  oblique  rhombic  prisms.  The  silico-fluoride  is  obtained 
in  crystalline  scales  on  adding  hydrofluosilicic  acid  to  any  so- 
luble salt  of  ammopalladammonium.    Oxide  of  ammopalladam- 

monium^  NHgPd .  O. —  By  decomposing  the  solution  of  the 
chloride  with  oxide  of  silver, — or  better,  the  sulphate  with 
hydrate  of  baryta,  a  strongly  alkaline  solution  is  obtained, 
which,  on  evaporation,  leaves  the  hydrated  oxide  in  the  form 
of  a  crystalline  mass,  though  not  quite  pure.  The  solution 
precipitates  the  salts  of  aluminium,  iron,  cobalt,  nickel,  and 
copper,  but  not  those  of  silver ;  expels  ammonia  from  cliloride 
of  ammonium,  on  boihng ;  and  absorbs  carbonic  acid  from 
the  air.  The  carbonate  obtained  in  this  manner,  or  by  de- 
composing the  chloride  with  carbonate  of  silver,  or  the 
sulphate  with  carl)onate  of  baryta,  crystallises  in  shining, 
colourless  prisms,  which  turn  yellow  a  little  above  212°;  the 
solution  is  strongly  alkaline,  and  gives  copious  precipitates 
with  salts  of  lime,  baryta,  copper,  and  silver.     The  sulphite^ 

NH2  (NH^)  Pd  .  SO3,  obtained  by  direct  combination,  or  by 
the  action  of  ammonia  on  sulphite  of  palladammonium,  forms 
small  prismatic  crystals,  sparingly  soluble  in  water,  insoluble 
in  alcohol,  and  turning  yellow  at  about  392°.  The  sulphate 
obtained  by  treating  palladous  sulphate  with  excess  of  am- 
monia, forms  small  colourless  prisms,  easily  soluble  in  water, 
but  insoluble  in  alcohol  (Hugo  MuUer).* 

*  Ann.  Ch.  Pharm.  Ixxxvi.  311. 


IlilDIUM.  391 


ESTIMATION    AND    SEPARATION    OF    PALLADIUM. 

Palladiuin  is  always  estimated  in  the  metallic  state.  It  is 
precipitated  from  its  solutions  in  the  form  of  cyanide  by 
means  of  a  solution  of  cyanide  of  mercury,  the  liquid  not 
containing  any  excess  of  acid.  The  precipitated  cyanide  of 
palladium  is  then  reduced  to  the  metallic  state  by  calcination. 

Palladium  may  be  separated  from  nearly  all  other  metals 
either  by  precipitation  as  cyanide,  or  by  precipitation  with 
hydrosulphuric  acid,  or  by  the  solubihty  of  its  oxide  in  am- 
monia. But  to  separate  it  from  copper,  with  which  it  is 
associated  in  platinum  ore,  the  two  metals  are  precipitated 
together  by  hydrosulphuric  acid,  and  the  precipitate,  while 
still  moist,  roasted,  together  with  the  filter,  as  long  as  sul- 
phurous acid  continues  to  escape.  The  metals  are  thereby 
converted  into  basic  sulphates,  which  must  be  dissolved  in 
hydrochloric  acid,  the  solution  mixed  with  nitric  acid  and 
chloride  of  potassium,  and  evaporated  to  dryness.  A  dark 
saline  mass  is  thus  obtained,  consisting  of  chloride  of  potas- 
sium, chloride  of  copper  and  potassium,  and  chloride  of  pal- 
ladium and  potassium  ;  and  on  treating  this  mass  mth  alcohol 
of  sp.  gr.  0-833,  the  two  former  salts  are  dissolved,  and  the 
double  chloride  of  palladium  and  potassium  remains. 


SECTION    III. 

IRIDIUM. 

Eq.  98-68,  or  1233-5;  Ir. 

The  black  scales  which  remain  when  native  platinum  is 
dissolved  in  aqua-regia,  were  discovered  by  Mr.  Smithson 
Tennant  to  contain  iridium  and  osmium.*     The  same  alloy 

*  PhU.  Trans.  1804. 


392  IRIDIUM. 

occurs  in  flat  white  metallic  grains  in  native  platinum.  Iri- 
dium has  also  been  observed  in  combination  with  about  20 
per  cent,  of  platinum^  crystallised  in  octohedrons,  which  are 
whiter  than  platinum,  and  are  said  to  have  a  greater  density, 
namely  22*66. 

The  separation  of  the  osmium  and  iridium  is  effected  by 
the  following  methods :  —  1 .  The  osmide  of  iridium  is  mixed 
with  an  equal  weight  of  common  salt,  and  subjected  to  the 
action  of  a  stream  of  chlorine  in  a  porcelain  tube  heated  to 
redness.  Double  chlorides  of  iridium  and  sodium,  and  of 
osmium  and  sodium,  are  then  formed ;  and  if  the  chlorine  is 
moist,  a  certain  quantity  of  osmic  acid,  which  volatilises,  and 
may  be  condensed  in  aqueous  ammonia.  The  mixture  of  the 
double  chlorides  is  detached  from  the  tube  and  boiled  with 
nitric  acid.  Osmic  acid  is  then  evolved,  and  may  be  con- 
densed in  an  alkaline  solution,  while  the  chloride  of  sodium 
and  iridium  remains  in  the  solution,  and,  when  mixed  with 
sal-ammoniac,  yields  a  precipitate  of  chloride  of  iridium  and 
ammonium,  which,  on  ignition,  leaves  pure  metallic  iridium 
(Wohler). — 2.  A  mixture  of  100  grammes  of  osmide  of 
iridium  and  300  grammes  of  nitre  is  placed  in  an  earthen 
crucible,  and  heated  to  bright  redness  for  an  hour,  the  re- 
sulting mixture  of  osmiate  and  iridiate  of  potash  poured  out 
on  a  cold  metal  plate,  then  introduced  into  a  tubulated  retort, 
and  distilled  with  a  large  excess  of  nitric  acid.  A  large 
quantity  of  osmic  acid  then  volatilises  and  condenses  in  the 
receiver  in  beautiful  white  ciystals.  As  soon  as  the  evolution 
of  osmic  acid  ceases,  water  is  added,  and  the  residue,  con- 
sisting of  oxide  of  iridium,  with  a  certain  quantity  of  oxide  of 
osmium,  is  collected  on  a  filter  and  boiled  with  aqua-regia, 
which  dissolves  the  two  metals  as  chlorides.  The  solution  is 
then  mixed  with  sal-ammoniac,  which  precipitates  chloride  of 
osmium  and  ammonium,  and  bichloride  of  iridium  and  am- 
monium ;  and  the  mixed  precipitate  suspended  in  water  and  ex- 
posed to  a  current  of  sulphurous  acid,  whereby  the  compound 


IRIDIUM.  393 

IrCl2.NIl4Cl,  is  converted  into  IrCl.NH^Cl,  which  dissolves, 
■while  the  chloride  of  osmium  and  ammonium  remains  un- 
altered and  does  not  dissolve  :  this  latter  chloride  yields  pure 
metallic  osmium  by  calcination.  The  solution  of  protochloride 
of  iridium  and  ammonium  leaves,  when  evaporated,  beautiful 
brown  crystals,  which  yield  metallic  iridium  by  calcination. 

Iridium  is  obtained  immediately  from  the  chloride,  by 
decomposing  that  salt  with  hydrogen  at  a  gentle  heat,  or  by 
exposing  it  alone  to  a  very  high  temperature,  in  the  form  of  a 
grey  metallic  powder,  much  resembling  spongy  platinum; 
also,  as  above  described,  from  the  chloride  of  iridium  and 
ammonium.  It  is  one  of  the  most  refractory  bodies  known, 
not  being  fused  by  the  oxyhydrogen  blowpipe.  Mr.  Chil- 
dren, however,  succeeded  in  fusing  a  portion  of  iridium  into 
a  globule,  by  the  discharge  of  a  very  large  voltaic  battery. 
This  globule  was  white  and  very  brilliant,  but  still  a  little 
porous;  its  density  was  18*68.  Iridium  is  neither  ductile 
nor  malleable ;  but  it  may  be  obtained  in  the  form  of  a  com- 
pact mass,  very  hard,  and  capable  of  taking  a  good  polish,  by 
moistening  the  pulverulent  metal  with  a  small  quantity  of 
water,  compressing  it  lightly  at  first  with  filtering  paper, 
afterwards  very  forcibly  in  a  press,  and  calcining  it  at  a  strong 
white  heat  in  a  forge  fire.  The  metal  thus  aggregated  is  very 
porous,  and  its  density  does  not  exceed  16*0.  Iridium  be- 
comes white  and  brilliant  by  strong  ignition,  without  fusion, 
and  is  afterwards  insoluble  in  acids.  If  reduced  by  hydrogen 
at  a  low  temperature,  it  oxidates  slowly  when  heated  to  red- 
ness, or  when  digested  in  aqua-regia.  This  metal  is  generally 
rendered  soluble  by  one  or  other  of  the  following  operations. 
It  is  calcined  with  hydrate  of  potash  or  nitre,  or  with  a 
mixture  of  these  salts,  which  gives  a  compound  of  sesqui- 
oxide  of  iridium  and  potassium.  Or,  the  metal  is  reduced  to 
a  fine  powder,  and  intimately  mixed  with  an  equal  weight  of 
chloride  of  potassium  or  sodium,  and  the  mixture  heated  to 
low  redness  in  a  stream  of  chlorine  gas.     The  metal  then 


391  IRIDIUM. 

combines  with  chlorine,  and  the  double  chloride  of  iridium 
and  potassium  or  sodium  is  formed,  which  is  soluble  in  water. 

Oxides  of  iridium. —  Iridium  forms  four  compounds  wiih 
oxygen,  which  are  obtained  by  decomposing  the  corresponding 
chlorides.  The  protoxide  of-  iridium^  IrO,  is  obtained  from 
the  chloride  produced  when  iridium  is  heated  in  chlorine  gas; 
also  by  precipitating  the  double  chloride  of  iridium  and  potas- 
sium (KCl .  IrCl)  with  carbonate  of  potash.  The  hydrate  is 
then  obtained  of  a  greenish  grey  colour,  which  is  soluble  in 
an  excess  of  the  alkaline  carbonate.  This  oxide  is  the  base 
of  a  class  of  salts.  The  sesquioxide  cf  iridium,  Ir203,  is 
formed  when  the  metal  is  calcined  with  hydrate  of  potash  or 
nitre.  Berzelius  recommends  as  the  best  process  for  pro- 
curing it,  to  mix  the  double  bichloride  of  iridium  and  potas- 
sium (KCl  +  IrCl2)  with  twice  its  weight  of  carbonate  of 
potash,  and  expose  it  to  a  low  red  heat.  On  dissolving  out 
the  alkaline  salt,  the  sesquioxide  remains  as  a  very  fine  pow- 
der, of  a  black  colour  with  a  shade  of  blue.  A  heat  above 
the  melting  point  of  silver  is  required  to  expel  the  oxygen 
from  this  oxide.  It  is  reduced  to  the  metallic  state  by  hydro- 
gen gas  at  the  usual  temperature,  an  effect  which  appears  to 
arise  from  the  oxide  of  iridium  having  the  property,  as  well  as 
the  metal,  to  determine  the  oxidation  of  hydrogen,  a  reaction 
which  causes  the  oxide  to  be  heated  to  the  temperature  at 
which  it  is  itself  reduced  by  hydrogen.  The  hydrate  of  this 
oxide  dissolves  in  acids  and  forms  a  particular  class  of  salts, 
the  solutions  of  which  are  sometimes  of  a  very  dark  colour, 
resembling  a  mixture  of  water  and  venous  blood. 

Bioxide  of  iridium,  or  Iridic  oxide,  IrOj. — A  solution  of 
sesquichloride  of  iridium  mixed  with  potash  yields  no  preci- 
pitate at  first ;  but  if  the  liquid  be  heated  out  of  contact  with 
the  air,  it  quickly  assumes  an  indigo  colour,  absorbs  oxygen 
from  the  air,  and  deposits  hydrated  iridic  oxide,  IrOg .  2H0, 
which  may  be  rendered  anhydrous  by  calcination.  This  oxide 
is  likewise  obtained  by  dissolving  the  hydrated  sesquioxide  in 


SALTS    OP    IRIDIUM.  395" 

potash,  and  treating  the  solution  with  an  acid.  A  greenish- 
blue  precipitate  is  then  formed,  which  gradually  absorbs 
oxygen  from  the  air,  and  assumes  an  indigo  colour  (Claus). 
This  oxide  forms  salts  whose  solutions  are  of  a  dark,  brown- 
red  colour  and  almost  opaque  when  concentrated,  but  reddish- 
yellow  when  dilute.  Hydrosulphuric  acid  decolorises  the 
solutions  at  first,  and  afterwards  forms  a  brovm  precipitate ; 
hydrosulphate  of  ammonia  also  forms  a  brown  precipitate. 
Potash  and  ammonia  decolorise  the  solution,  and  produce 
only  a  slight  black  precipitate ;  but  the  liquid,  on  exposure  to 
the  air,  soon  acquires  a  very  fine  blue  colour.  Carbonate  of 
potash  forms  a  red-brown  precipitate,  which  gradually  dis- 
solves, the  liquid  afterwards  turning  blue  when  exposed  to 
the  air.  Carbonate  of  ammonia  imparts  a  blue  colour  to  the 
liquid  under  the  influence  of  the  air.  Chloride  of  ammonium 
forms  a  dark,  cherry-red  pulverulent  precipitate  of  bichloride 
of  iridium  and  ammonium.  Ferrocyanide  of  potassium  and 
protosulphate  of  iron  decolorise  the  solution.  Protochloride 
of  tin  forms  a  light  brown  precipitate.  Zinc  precipitates 
metallic  iridium  as  a  black  powder. 

Teroxide  of  iridium,  IrOg,  is  formed  in  small  quantity 
when  the  alloy  of  osmium  and  iridium  fused  in  nitre  is 
digested  in  aqua-regia.  The  double  terchloride  of  iridium 
and  potassium  then  formed  yields  a  rose-red  solution,  which, 
when  treated  with  an  alkali,  slowly  deposits  the  teroxide 
as  a  greenish-yellow  precipitate,  retaining,  however,  a  cer- 
tain quantity  of  the  alkali.  The  salts  of  the  protoxide 
and  teroxide  afford  blue  and  purple  solutions  when  mixed, 
depending  probably  on  the  formation  of  one  or  more  com- 
binations of  these  oxides.  The  name  iridium  (from  Iris)  was 
applied  to  this  metal,  from  the  variety  of  colours  which  its 
preparations  exhibit. 

Sulphides  of  iridium,  corresponding  with  the  oxides  of  the 
same  metal,  have  been  formed. 

Chlorides  of  iridium.  —  The  protochloride,  IrCl,  is  formed 

VOL.  II.  E  E 


396  IRIDIUM. 

when  iridium  in  powder  is  heated  to  low  redness  in  chlorine 
gas.  As  thus  prepared,  it  is  insoluble  in  water,  but  slightly- 
soluble  in  hydrochloric  acid.  It  forms  double  salts  with  the 
chlorides  of  potassium,  ammonium,  and  sodium. 

The  sesquichloride,  Ir2Cl3,  is  prepared  by  dissolving  the 
sesquioxide  in  hydrochloric  acid.  It  is  black,  deliquescent, 
and  does  not  crystallise.  It  forms  soluble  double  chlorides, 
which  are  decomposed  by  ebullition  into  iridous  double  chlo- 
rides (containing  IrCl),  which  remain  in  solution,  and  iridic 
double  chlorides  (containing  IrClg),  which  are  precipitated. 
Glaus  has  obtained  the  compounds,  3KC1 .  Ir2Cl3  -h  6H0  ; 
3NH4CI .  Ir^Clg  +  3H0 ;  and  3NaCl .  Ir2Cl3  +  2 IHO. 

The  bichloride,  IrCl2,  is  obtained  by  dissolving  very  finely- 
divided  iridium,  or  one  of  its  oxides,  in  aqua-regia.  the  liquid 
being  heated  to  the  boiling  point.  It  dissolves  in  water, 
forming  a  reddish-yellow  solution.  It  combines  with  other 
chlorides,  forming  very  definite  salts.  The  potassium-salt, 
chloridiate  of  j^otassium,  IrClg.KCl.IIO,  crystallises  in  black 
octohedrons,  yielding  a  red  powder,  and  soluble  in  water,  to 
which  it  imparts  a  red  colour.  Chloridiate  of  ammoniu7n, 
IrClg .  NH4CI  .HO,  is  obtained,  on  mixing  the  solutions  of 
the  two  chlorides,  as  a  very  dark  brown  precipitate,  which 
dissolves  in  boiling  water,  and  crystallises  in  octohedrons  on 
cooling.  Its  colouring  power  is  very  great,  1  part  of  it 
sufficing  to  impart  a  distinct  coloration  to  40,000  parts  of 
water.  The  red  colour  often  exhibited  by  chloroplatinate  of 
ammonium  is  due  to  traces  of  this  salt.  Chloridiate  of  am- 
monium dissolves  in  sulphurous  acid,  and  is  thereby  converted 
in  a  soluble  and  crystallisable  compound  of  NH4CI,  and 
IrCl ;  the  separation  of  iridium  and  osmium  depends  upon 
this  property.  Bichloride  of  iridium,  free  or  combined  with 
other  chlorides,  is  also  reduced  to  the  s':ate  of  protochloride 
by  potash,  hydrosulphuric  acid,  ferrocyanide  of  potassium, 
and  alcohol.    According  to  Claus,*  the  bichloride  is  converted 

*  Liebig  and  Kopp's  Jahresbericht,  1855,  p.  427. 


AMMOx\IACAL    COMPOUNDS    OF    IRIDIUM.  397 

by  potash  into  tlie  olive-green  sesquichloride,  hypochlorite  of 
potash  being  formed  at  the  same  time.  The  alkaline  solution 
when  heated  becomes  colourless,  and  afterwards  violet-red, 
and  yields  a  blue  precipitate  of  the  hydrated  bioxide;  the 
decolorised  alkaline  solution,  mixed  with  a  few  drops  of 
alcohol  and  heated,  deposits  metallic  iridium.  Nitrate  of 
silver  added  to  the  solution  of  the  bichloride  forms  a  blue  pre- 
cipitate, which  quickly  loses  its  colour  and  passes  into  the 
compound  Ir2Cl3  .  3AgCl.  Mercurous  nitrate  forms  a  light 
ochre-yellow  precipitate  of  IrgClg  .  3Hg2Cl. 

Terchloride  of  iridium,  IrClg,  is  formed  by  treating  an 
oxide  or  a  lower  chloride  of  iridium  with  very  strong  aqua- 
regia,  at  a  temperature  not  exceeding  104°  or  122°  (40°  or 
50°  C).  Its  colour  is  a  deep  brown,  nearly  approaching  to 
black;  it  is  soluble  in  water,  and  deliquescent.  It  forms 
double  chlorides  with  the  chlorides  of  the  alkali-metals. 

Carburet  of  iridium. — When  a  coherent  mass  of  iridium  is 
held  in  the  flame  of  a  spirit  lamp,  black  masses  appear  on  its 
surface,  which  are  a  carburet,  containing  19*83  per  cent,  of 
carbon,  or  IrC^.     The  carbon  bums  off  readily  in  the  air. 

Iridic  sulphate  is  obtained  by  dissolving  bisulphide  of 
iridium  in  nitric  acid  and  expelling  the  excess  of  acid  by 
evaporation.  It  dissolves  in  water  and  alcohol,  forming 
orange-yellow  solutions,  which  on  evaporation  leave  the  salt 
in  the  form  of  a  syrupy  uncrystallisable  mass. 

Ammoniacal  Compounds  of  Iridium, — Ammonio-iridious 

chloride,  NH3  .  IrCl,  or  Chloride  of  iridammonium,  NH3lr .  CI. 
— Prepared  by  heating  bichloride  of  iridium  till  it  is  converted 
into  protochloride,  dissolving  the  brown  resinous  residue  in 
carbonate  of  ammonia,  and  adding  hydrochloric  acid  in  slight 
excess.  The  compound  then  separates  in  the  form  of  a  yellow 
granular  precipitate,  insoluble  in  water.  The  oxide  correspond- 
ing to  this  chloride  has  not  been  obtained  in  the  free  state. 

The  sulphate  NH3lr  .  SO4  is  obtained  by  heating  the  chloride 

£  £   2 


398  IRIDIUM. 

with  dilute  sulphuric  acid.  It  crystallises  in  large  orange- 
yellow  laminae,  easily  soluble  in  water.     Biammonio-iridiotis 

chloride,    2NH3  .  IrCl,    or    Chloride   of  ammiridammonium, 

^ ' 

NH2(NH4)Ir.  CI,  is  obtained,  as  a  white  precipitate,  by 
boiling  the  compound,  NHglr .  CI,  with  excess  of  ammonia. 
Treated  with   moderately   strong  sulphuric   acid,   it   yields 


the  corresponding  sulphate,  NH2(NH4)Ir .  SO4,  in  rhombic 
prisms ;  and,  by  decomposing  this  salt  with  nitrate  of  baryta, 
or  decomposing  the  chloride  with  nitric  acid,  the  nitrate  is 
obtained  in  yellow  needles,  which  dissolve  readily  in  water, 
melt  when  heated,  and  then  suddenly  decompose  T^dth  flame. 

A  chloronitraie  of  ammiridammonium,  NH2(NH4)Ir.|    ^p 

or  nitrate  of  ammochlonHdammonium,  NH2(NH4)(IrCl).NOg, 
analogous  to  Groses  platinum-nitrate  (p.  379),  is  obtained  as  a 
yellowish,  crystalline,  granular  mass,  by  heating  the  chloride 
of  iridammonium,  NHglr .  CI,  with  strong  nitric  acid  ;  when 
recrystallised  from  water,  it  forms  shining  yellow,  laminar 

crystals.    Bichloride  of  ammiridammonium,  NH2(NH^)Ir  .  Clj, 

. ^ 

or  chloride  of  ammO'Chloriridammonium,'^!^^^^ ^^^^^)  •  CI, 
is  obtained  by  treating  the  last-mentioned  salt  with  hydro- 
chloric acid,  in  the  form  of  a  violet  precipitate,  which  dissolves 
readily  in  hot  water,  and  separates  from  the  solution  in  violet 
crystals.  Nitrate  of  silver  added  to  the  solution  throws  down 
only  half  the  chlorine.  The  nitrate,  treated  with  dilute  sul- 
phuric acid,  yields  the  chlorosulphate  of  ammiridammonium 
in  delicate  greenish,  needle-shaped  crystals  (Skoblikoff). 

The  compound  SNH,  .  IrClg,  or  ^H2(NHJIr|  ^^^^  .^  ^^_ 

NH(NHj2lr^ 
taincd  by  mixing  a  dilute  solution  of  Ir2C]3  +  SNH^Cl,  mixed 

with  excess  of  ammonia,  and  leaving  the  mixture  in  a  well- 
closed  and  completely  filled  bottle  for  some  weeks  in  a  warm 
place;  heating  the  liquid,  which  has  then  acquired  a  rose- 


ESTIMATION    OF    IRIDIUM.  399 

colour,  to  expel  the  excess  of  ammonia;  neutralising  with, 
hydrochloric  acid ;  evaporating  to  dryness ;  and  treating  the 
greenish  yellow  residue  with  cold  water  to  extract  the  chloride 
of  ammonium.  A  light  flesh-coloured,  finely  crystalline 
powder  then  remains,  which,  when  dissolved  in  boiling  water, 
acidulated  with  hydrochloric  acid,  yields,  on  cooling,  a  crys- 
talline precipitate  of  5NH3  .  Ir2Cl3  mixed  with  sesquichloride 
of  iridium.  This  compound  when  dissolved  in  a  boiling  solu- 
tion of  ammonia,  is  partially  decomposed,  with  separation  of 
blue  hydrated  bioxide  of  iridium ;  when  digested  with  water 
and  oxide  of  silver,  it  yields  a  rose-coloured  alkaline  solution 
of  the  base  5NH3  .  Ir203.  This  solution,  saturated  with  various 
acids,  yields  : — the  carbonate,  5NH3 .  Ir203  .  3C02  +  3HO,  in 
the  form  of  a  finely  crystalline  powder,  having  a  light  flesh- 
colour  and  alkaline  reaction;  i\iQ nitrate,  5NH3.Ir2O3.3NO5, 
in  indistinct,  light  flesh-coloured,  neutral  prisms ;  and  the 
sulphate,  5NH3  .  Ir203  .  380^,  as  a  neutral  crystalline  salt  of 
similar  colour.     All  these  salts  are  soluble  in  water  (Claus). 


ESTIMATION    AND    SEPARATION    OF    IRIDIUM. 

The  quantitative  estimation  of  iridium  is  effected  in  the 
same  manner  as  that  of  platinum,  viz.  by  precipitating  with 
sal-ammoniac  and  igniting  the  precipitate.  The  same  method 
serves  to  separate  iridium  from  all  the  preceding  metals 
except  platinum.  The  separation  of  these  two  metals  is 
effected  by  the  method  already  described  for  the  preparation 
of  pure  platinum  (p.  336) ;  viz.  by  precipitating  with  chloride 
of  potassium,  fusing  the  precipitate  with  carbonate  of  potash, 
and  dissolving  out  the  platinum  with  aqua-regia. 


£  E   3 


400  OSMIUM. 


SECTION    IV. 

OSMIUM. 

Eq,  99-56  or  12445 ;    Os. 

In  the  treatment  of  the  aUoy  of  iridium  and  osmium,  the 
latter  is  separated  as  a  volatile  oxide,  or  osmic  acid  (p.  394) . 
To  obtain  the  metal,  a  solution  of  osmic  acid  is  mixed  with 
hydrochloric  acid,  and  digested  with  mercury  in  a  well  closed 
bottle  at  a  temperature  of  104°  (40°  Cent.).  The  osmium  is 
reduced  by  the  mercury,  and  an  amalgam  formed,  which  is 
distilled  in  a  retort,  through  which  a  stream  of  hydrogen 
is  passed,  till  all  the  mercury  and  calomel  formed  are  re- 
moved :  osmium  then  remains  as  a  black  powder  without 
metallic  lustre.  Metallic  osmium  is  also  obtained  by  igniting 
the  sesquichloride  of  osmium  and  ammonium  mixed  with  sal- 
ammoniac. 

When  rendered  coherent,  osmium  is  a  white  metal,  less 
brilliant  than  platinum,  and  very  easily  pulverised.  Its  den- 
sity is  about  10.  As  obtained  from  the  amalgam,  osmium  is 
highly  combustible  ;  when  a  mass  of  it  is  ignited  at  a  point, 
it  continues  to  redden,  and  burns  without  residue,  being  con- 
verted into  the  volatile  oxide  or  osmic  acid.  Osmium  in  the 
same  condition  is  oxidated  by  nitric  acid  or  aqua-regia,  and 
the  osmic  acid  formed  distills  over  with  the  water  and  acid. 
But  after  being  exposed  to  a  red  heat,  osmium  becomes  much 
less  combustible  in  air,  and  is  not  oxidated  by  the  humid  way, 
resembling  silicon  and  titanium  in  that  respect.  Six  different 
oxides  of  this  metal  have  been  obtained,  namely,  OsO; 
OS2O3  ;  OSO2 ;  OSO3  ;  OsO^  ;  and  OsOg.  The  three  lowest 
of  these  oxides  are  analogous  in  composition  to  the  oxides 
of  iridium. 

Chlorides  and  oxides  of  osmium. — When  osmium  is  heated 
in  a  long  glass  tube  by  a  spirit  lamp,  and  chlorine  gas  passed 


CHLORIDES    AND    OXIDES    OF   OSMIUM.  401 

over  it,  two  chlorides  are  formed,  which  condense  separately 
in  the  tube,  owing  to  a  difference  in  their  volatility.  The 
protochloride,  OsCl,  which  is  the  least  volatile,  crystallises  in 
needles  of  a  deep  green  colour.  It  is  deliquescent,  and  forms 
a  green  solution  remarkable  for  its  beauty.  This  solution  is 
instantly  discoloured  by  great  dilution,  metallic  osmium  being 
deposited,  and  hydrochloric  and  osmic  acids  remaining  in 
solution.  Chloride  of  osmium  combines  with  alkaline  chlorides, 
and  acquires  greater  stability.  The  protoxide,  OsO,  is  obtained 
by  adding  potash  to  a  solution  of  protochloride  of  osmium  and 
potassium;  after  some  hours,  a  deep  green,  almost  black, 
powder  is  precipitated,  which  is  the  hydrated  oxide.  This 
hydrate  contains  alkali.  It  dissolves  slowly  but  completely  in 
acids,  and  gives  solutions  of  a  deep  green  colour. 

Sesquioxide  of  osmium,  OS2O3,  is  not  known  in  the  separate 
state ;  but  when  a  mixture  of  osmic  acid  and  ammonia  is  kept 
for  some  hours  at  a  temperature  of  100°  to  120°,  nitrogen  gas 
is  evolved,  and  a  black  substance  is  deposited,  containing 
the  sesquioxide  in  combination  with  ammonia.  It  dissolves 
slowly  in  acids,  and  forms  yellowish  brown  solutions,  which 
become  brown-black  when  they  contain  much  oxide.  The 
metal  is  not  precipitated  from  these  solutions  by  zinc  or  iron. 
The  corresponding  sesquichloride  of  osmium  is  obtained  in 
combination  with  chloride  of  potassium  as  a  double  salt, 
when  the  preceding  oxide  containing  ammonia  is  dissolved  in 
hydrochloric  acid,  and  evaporated  to  dryness ;  the  compound 
is  not  crystalline. 

Bichloride  of  osmium,  OsClg,  is  the  more  volatile  chloride 
produced  when  osmium  is  heated  in  chlorine.  It  condenses 
as  a  dark  red  floury  powder.  Exposed  to  air,  it  attracts  a 
little  moisture,  and  forms  dendritic  crystals.  It  is  soluble  in 
a  small  quantity  of  water,  giving  a  yellow  solution,  but  is  de- 
composed by  a  large  quantity,  like  the  protochloride.  The 
bichloride  of  osmium  and  potassium  is  prepared  in  the  same 
manner  as  the  corresponding  salt  of  iridium.     In  powder,  it 

E  E   4 


402  OSMIUM. 

is  of  a  red  colour  like  minium,  but  forms  also  the  usual  octo- 
hedral  crystals,  KCl .  OSCI2,  which  are  brown.  A  solution  of 
this  double  salt,  mixed  with  carbonate  of  potash  or  soda, 
affords  after  a  time,  or  immediately,  if  heated,  the  correspond- 
ing bioxide  of  osmium  or  os-mic  oocide,  OSO2,  as  a  brown 
powder,  which  appears  black  when  collected.  This  oxide,  like 
the  peroxide  of  iridium,  is  reduced  by  hydrogen  at  ordinary 
temperatures.  It  is  a  base  capable  of  uniting  with  acids  at 
the  moment  of  its  formation. 

Osmic  sulphate  is  obtained  by  treating  one  of  the  sulphides 
of  osmium  with  nitric  acid ;  when  diied  as  completely  as  pos- 
sible, it  forms  a  dark  yellowish  brown  syrup,  which  dissolves 
in  water.  The  reactions  of  osmic  salts  {e.  g.  of  the  bichloride 
of  osmium  and  potassium)  in  solution,  are  as  follows  :  — 
Potash  forms  a  black  precipitate,  slowly  in  the  cold,  im- 
mediately on  boiling;  ammonia^  a  brown  precipitate,  after 
some  time ;  carbonate  of  potash,  the  same  ;  chloride  of  am- 
monium, a  red  precipitate ;  protochloride  of  tin,  a  brown 
precipitate ;  mercurous  nitrate,  yellowish  white ;  nitrate  of 
silver,  dark  olive-green;  hydrosulpJiuric  acid,  a  yellowish 
brown  precipitate  after  some  time ;  hydrosulphate  of  ammonia, 
a  yellowish  brown  precipitate  insoluble  in  excess.  No  pre- 
cipitate is  formed  by  oxalic  acid,  ferrocyanide  or  ferricyanide 
of  potassium,  or  ferrous  sulphate.  Zinc  throws  down  part  of 
the  osmium  in  the  metallic  state.  Iodide  of  potassium  does 
not  form  any  precipitate,  but  imparts  a  deep  purple-red 
colour,  which  does  not  disappear  when  the  liquid  is  heated. 
Tannic  acid  imparts  a  deep  blue  colour. 

Osmious  acid,  OsOg. — This  acid  is  not  known  in  the 
separate  state,  being  resolved  at  the  moment  of  separation 
from  its  combinations,  into  osmic  acid  and  osmic  oxide, 
2OSO3  =  OSO4  +  OSO2.  Osmite  of  potash,  KO  .  OsOg  + 
2H0,  is  obtained  by  the  action  of  reducing  agents  on  the 
osmiate ;  thus,  when  a  few  drops  of  alcohol  are  added  to  a 
solution  of  osmiate  of  potash,  the  osmite  is  precipitated  in  the 


OSMIC    ACID.  403 

form  of  a  rose-coloured  crystalline  powder,  a  strong  odour  of 
aldehyde  being  at  the  same  time  evolved,  due  to  the  oxidation 
of  the  alcohol.  Osmite  of  potash  may  be  obtained  in  octo- 
hedral  crystals  of  considerable  size,  by  mixing  a  solution  of 
osmiate  with  nitrite  of  potash,  and  leaving  the  mixture  to 
evaporate  slowly.  The  salt  is  likewise  obtained  by  dissolving 
osmic  oxide  in  osmiate  of  potash.  It  is  rose-coloured,  soluble 
in  water,  insoluble  in  alcohol  and  ether,  permanent  in  dry  air, 
but  changes  into  osmiate  under  the  influence  of  air  and  water. 
Chlorine  converts  it  into  osmic  oxide  and  osmiate  of  potash. 
It  is  decomposed  by  acids,  even  by  the  weakest,  osmic  oxide 
being  precipitated  and  osmic  acid  evolved.  Sulphurous  acid 
introduced  into  a  solution  of  this  salt,  previously  rendered 
alkaline,  throws  down  a  yellow  crystalline  precipitate,  con- 
taining a  salt  whose  acid  is  formed  of  osmium,  oxygen,  and 
sulphur.  Chloride  of  ammonium  decomposes  osmite  of  potash, 
forming  a  nearly  insoluble  yellow  salt,  NH^Cl .  OSO2NH2, 
which  may  be  regarded  as  a  compound  of  sal-ammoniac  with 
osmiamide,  OSO2NH2.  This  compound,  heated  in  a  stream  of 
hydrogen,  gives  off  ammonia  and  sal-ammoniac,  and  leaves 
metallic  osmium.  Osmite  of  soda  is  prepared  in  the  same 
manner  as  osmite  of  potash,  but  does  not  crystallise  so  easily ; 
its  solutions  are  rose-coloured.  Osmious  acid  does  not  com- 
bine with  ammonia;  the  osmites  of  potash  and  soda  are 
rapidly  reduced  by  ammonia. 

A  terchloride  of  osmium  has  been  obtained  in  combination 
with  chloride  of  ammonium,  as  a  double  salt,  when  osmic  acid 
is  saturated  with  ammonia,  and  treated  after  a  while  with  ex- 
cess of  hydrochloric  acid,  mercury  being  also  placed  in  contact 
with  it.  After  a  few  days,  the  liquid  loses  the  odour  of  osmic 
acid,  and  when  evaporated  to  dryness,  leaves  the  double  salt 
in  brown  dendritic  crystals. 

Osmic  acid,  OSO4,  or  the  volatile  oxide  of  osmium,  is  best 
obtained  by  the  combustion  of  osmium  in  a  glass  tube  through 
which  a  stream  of  oxygen  gas  is  passed ;  it  is  also  obtained 


404  OSMIUM. 

by  the  action  of  nitric  acid  on  osmium,  and  in  the  decomposi- 
tion of  osmites  or  osmates  by  acids.  It  condenses  in  long, 
coloui'less,  regular  prismatic  needles.  The  odour  of  this  com- 
pound is  extremely  acid  and  penetrating,  resembling  that  of 
the  chloride  of  suiphiu*.  It-  was  from  this  property  of  its 
acid,  which  is  so  constantly  observed  when  the  oxidable  com- 
pounds of  osmium  are  heated  in  air,  that  osmium  obtained  its 
name  (from  oa-fios,  odour).  Its  taste  is  acrid  and  burning,  but 
not  acid.  It  becomes  soft  like  wax  by  the  heat  of  the  hand, 
melts  into  a  colourless  liquid  like  water  considerably  below 
212°,  and  enters  into  ebullition  a  very  little  above  its  point  of 
fusion.  It  is  dissolved  slowly,  but  in  considerable  quantity, 
by  water.  The  solution  has  no  acid  reaction.  Osmic  acid  is 
also  soluble  in  alcohol  and  ether,  but  these  solutions  are  apt 
to  deposit  metallic  osmium.  It  is  a  weak  acid,  being  incapable 
of  displacing  carbonic  acid  from  the  carbonates,  in  the  humid 
way,  but  forms  a  class  of  salts,  the  osmiates.  Osmic  acid  is 
expelled  by  heat  from  most  of  its  combinations  with  bases. 

An  acid  containing  more  oxygen  than  osmic  acid,  and 
apparently  having  the  formula  OsOg,  is  formed  by  submitting 
the  osmiates  to  the  action  of  oxygen  and  oxidising  agents. 
It  is  very  unstable ;  its  potash  and  soda-salts  have  a  dark 
brown  colour,  and  sometimes  crystallise  in  the  alkaline 
liquids.  If  the  formida  OsOg  be  correct,  the  oxidation- 
series  of  osmium  will  present  remarkable  analogies  with 
those  of  nitrogen,  phosphorus,  and  arsenic  (Fremy). 

Osmiamic  acid,  OS2NO5. —  Formed  by  the  action  of  am- 
monia on  osmic  acid,  2OSO4  +  NH3  .  OsgNOg  +  3H0.  Its 
potash-salt  is  obtained  by  adding  ammonia  to  a  hot  solution 
of  osmic  acid  in  excess  of  potash  j  the  deep  orange  colour  of 
the  liquid  soon  changes  to  light  yellow,  and  osmiamate  of 
potash  separates  in  the  form  of  a  yellow  crystalline  powder. 
The  osmiamates  of  the  alkalies  and  alkaline  earths  and  the 
zinc-salt  are  soluble  in  water ;  the  lead,  mercury,  and  silver- 
salts  insoluble.    The  aqueous  acid  is  obtained  by  decomposing 


ESTIMATION    OF    OSMIUM.  405 

the  baryta-salt  with  sulphuric,  or  the  silver-salt  with  hydro- 
chloric acid.  It  may  be  kept  for  some  days  when  dilute^  but 
soon  decomposes  in  the  concentrated  state.  It  is  a  powerful 
acid,  decomposing  not  only  the  carbonates,  but  even  chloride  of 
potassium.  Fritzsche  and  Struve,*  who  discovered  this  acid, 
assign  to  it  the  formula  OS2NO4,  regarding  it  as  a  compound 
of  nitride  of  osmium  with  osmic  acid ;  OsN  .  OSO4.  Gerhardt, 
on  the  contrary,t  assigns  to  it  the  formula  above  given,  viz., 
OS2NO5,  which  is  the  more  probable  of  the  two,  inasmuch  as, 
if  Fritzsche  and  Struve's  were  correct,  the  formation  of  the 
acid  must  be  attended  with  the  evolution  of  1  eq.  oxygen; 
but  they  particularly  observe  that  no  escape  of  gas  takes 
place. 

Sulphides  of  osmium. —  Osmium  has  a  great  affinity  for 
sulphur,  and  burns  in  its  vapour.  Five  sulphides  of  osmium 
are  known,  corresponding  to  all  the  oxides  except  the  highest, 
viz.,  OsS,  OS2S3,  OSS2,  OSS3,  OSS4.  The  first  four  of  these 
sulphides  are  obtained  by  decomposing  the  corresponding 
chlorides  with  hydrosulphuric  acid.  The  tetrasulphide  is  pre- 
pared by  passing  hydrosulphuric  acid  gas  into  a  solution  of 
osmic  acid  :  it  is  a  sulphur-acid,  completely  insoluble  in  water ; 
whereas  the  others  are  sulphur  bases,  slightly  soluble  in  water, 
and  forming  deep  yellow  solutions. 


ESTIMATION    AND    SEPARATION    OF    OSMIUM. 

Osmium  is  generally  estimated  in  the  metallic  state.  The 
best  mode  of  separating  it  from  the  metals  with  which  it  is 
usually  accompanied,  is  to  volatilise  it  in  the  form  of  osmic 
acid — by  distillation  with  aqua-regia,  if  the  compound  be  per- 
fectly soluble  therein,  or  by  roasting  in  a  stream  of  oxygen — 
receiving  the  vapours  of  osmic  acid  in  a  strong  solution  of 

*  J.  pr.  Chem.  xli.  97. 

t  Compt.  rend,  de  Trans,  en  Chimie,  1847,  304. 


406  ESTIMATION    OF    OSMIUM. 

potash ;  and  to  reduce  this  salt,  by  the  addition  of  a  few  drops 
of  alcohol,  to  osmite  of  potash,  which  is  insoluble  in  the 
alcoholic  liquor.  The  osmite  of  potash  is  then  digested 
in  a  cold  solution  of  sal-ammoniac,  whereby  the  compound 
NH4CI .  OSO2NH2  is  produced,  and  the  osmium  reduced  to 
the  metallic  state  by  igniting  this  last-mentioned  compound 
in  a  current  of  hydrogen  gas  (Fremy). 

Another  mode  of  proceeding  is  to  condense  the  acid  vapours 
evolved  by  distilling  a  compound  of  osmium  with  aqua-regia 
in  a  well-cooled  receiver,  and  precipitate  the  osmium  from 
the  solution  by  metallic  mercury.  A  precipitate  is  thereby 
obtained  consisting  of  calomel,  a  pulverulent  amalgam  of 
osmium,  and  metallic  mercury  containing  a  very  small  quan- 
tity of  osmium.  This  mixture  is  heated  in  a  glass  bulb, 
through  which  a  stream  of  hydrogen  is  passed,  whereupon  the 
mercury  and  its  chloride  volatilise,  and  metallic  osmium  is 
left  in  the  form  of  a  black  powder.  The  liquid,  however, 
still  retains  a  small  quantity  of  osmium,  which  may  be  iso- 
lated by  saturating  the  liquid  with  ammonia,  evaporating  to 
dryness,  and  calcining  the  residue  (Berzelius).  The  osmium 
may  also  be  precipitated  from  the  distilled  liquid  l)y  hydro- 
sulphuric  acid,  the  solution,  after  complete  saturation,  being 
left  for  several  days  in  a  stoppered  bottle,  till  the  sulphide  of 
osmium  is  completely  deposited.  The  sulphide  is  then  washed, 
dried,  and  weighed ;  but  as  it  is  apt  to  retain  moisture,  and, 
moreover,  oxidises  to  a  certain  extent  in  the  air,  the  method 
is  not  very  exact.  It  is  recommended,  however,  for  the 
estimation  of  small  quantities  of  osmium,  the  method  of 
precipitating  by  mercury  being  better  adapted  for  larger 
quantities  (Berzelius). 


OXIDES   or   KHODIUM.  407 


SECTION    V. 

RHODIUM. 

Eq.  52  or  651-4;  R. 

This  metal  was  discovered,  by  WoUaston,  in  the  ore  of 
platinum.  He  found  the  ore  from  Brazil  to  contain  0*4  per 
cent ;  native  platinum  from  another  locality  has  been  found 
with  as  much  as  3  per  cent,  of  rhodium. 

After  the  precipitation  of  the  palladium  from  the  solution 
of  native  platinum,  by  cyanide  of  mercury,  the  solution,  in 
order  to  obtain  the  rhodium,  may  be  mixed  with  carbonate  of 
soda  and  excess  of  hydrochloric  acid,  and  evaporated  to  dry- 
ness. The  cyanide  of  mercury  in  excess  is  decomposed  by  the 
hydrochloric  acid,  and  converted  into  chloride  of  mercury. 
The  dried  mass  is  reduced  to  a  very  fine  powder,  and  washed 
with  alcohol  of  density  0*837,  which  takes  up  the  double 
chlorides  of  sodium  with  platinum  and  iridium,  the  copper  and 
the  mercury,  but  leaves  the  double  chloride  of  rhodium  and 
sodium  in  the  form  of  a  fine  deep  red  powder.  The  rhodium 
is  most  easily  reduced  by  gently  heating  the  double  chloride 
in  a  stream  of  hydrogen  gas,  and  afterwards  washing  out  the ' 
chloride  of  sodium  by  water. 

Rhodium,  when  rendered  coherent,  is  a  white  metal  like 
platinum;  its  density  is  about  10*6.  It  is  brittle  and  very 
hard,  and  may  be  reduced  to  powder.  When  pure,  it  is  not 
dissolved  by  any  acid ;  but  when  alloyed  with  certain  metals, 
such  as  platinum,  copper,  bismuth,  or  lead,  and  exposed  to 
aqua-regia,  it  dissolves  along  with  those  metals.  When  fused 
with  gold  or  silver,  however,  it  is  not  dissolved  with  the  other 
metal.  But  the  most  eligible  mode  of  rendering  rhodium 
soluble,  is  to  mix  it  in  fine  powder  with  chloride  of  potassium 
or  sodium,  and  to  heat  the  mixture  to  low  redness  in  a  stream 
of  chlorine  gas.     A  double  chloride  is  then  formed,  as  with 


408  RHODIUM. 

the  other  platinum  metals  in  similar  circumstances,  which  is 
very  soluble  in  water.  The  solutions  of  rhodium  have  a 
beautiful  red  colour,  the  circumstance  from  which  the  metal 
derives  its  name  (from  pbBov,  a  rose) .  Rhodium  may  also  be 
rendered  soluble  in  the  dry  way,  by  fusing  it  with  bisulphatc 
of  potash,  when  the  metal  is  oxidated  with  escape  of  sul- 
phurous acid  gas.  Rhodium  is  the  most  oxidable  of  the 
platinum  metals,  combining  with  oxygen  when  heated  to 
redness  in  an  open  vessel,  and  very  readily  when  in  fine 
powder  and  heated  to  a  cherry-red  heat.  It  appears  to  form 
two  oxides,  the  rhodous  and  the  rhodic,  of  which,  however, 
the  last  only  has  been  completely  isolated. 

Oxides  of  rhodium.  —  The  protoodde  or  rhodous  oxide,  RO, 
is  formed  when  rhodium  is  ignited  in  contact  with  the  air. 
One  hundred  parts  of  rhodium  thus  treated  quickly  increase 
to  115-3  parts,  corresponding  to  the  protoxide;  then  slowly, 
if  the  ignition  be  continued,  to  11807  parts;  a  black  powder 
being  formed,  consisting  of  3R0  .  R2O3  (Berzelius). 

Rhodic  oxide,  R2O3,  is  produced  when  the  metal  is  ignited 
with  hydrate  of  potash  and  a  little  nitre,  in  a  silver  crucible. 
The  metal  swells  up,  assumes  a  coffee-brown  colour,  and  is 
converted  into  a  compound  of  rhodic  oxide  and  potash,  which 
must  be  washed  with  water,  and  afterwards  digested  in  hydro- 
chloric acid ;  the  hydrated  oxide  remains  of  a  grey  colour, 
with  a  shade  of  green,  and  insoluble  in  acids.  The  same 
hydrated  oxide,  as  obtained  from  the  double  chloride  of  rho- 
dium and  potassium  or  sodium,  by  precipitation  with  an 
alkali  and  evaporation,  dissolves  slowly  in  acids,  together  with 
a  certain  quantity  of  alkali  which  is  attached  to  it,  assuming 
a  yellow  coloiir,  and  producing  double  salts.  The  solution  in 
hydrochloric  acid  is  also  pale,  although  it  contains  chloride 
of  potassium,  while  a  solution  of  the  double  chloride,  pre- 
pared in  the  way  formerly  mentioned,  has  a  fine  red  colour. 
Hence  Berzelius  infers  that  there  are  two  isomeric  modifi- 
cations of  this  oxide,  whose  compounds,  when  in  solution,  are 


SALTS    OF    RHODIUM.  409 

respectively  yellow  and  rose-coloured.  Hydrated  rhodic  oxide 
contains  one  atom  of  water,  ^2^3  -HO.  Two  compounds  of 
rhodic  oxide  with  the  protoxide  of  the  same  metal  appear 
to  exist :  ^2^3  •  3^0^  ^^^  ^^2^3  •  2K-0.  The  known  com- 
pounds of  rhodium  are  not  isomorphous  with  compounds  of 
platinmn ;  but  this  may  arise  from  these  two  metals  affecting 
combination  in  different  proportions,  so  that  their  compounds 
are  not  analogous  in  composition.  Their  association  and 
resemblance  in  other  respects  afford  a  strong  presumption  of 
their  being  isomorphous  bodies. 

Solutions  of  rhodic  salts  yield,  with  hydrosulphuric  acid,  a 
brown  precipitate  of  protosulphide,  which  is  slowly  deposited ; 
with  hydrosulphate  of  ammonia  a  brown  precipitate,  insoluble 
in  excess ;  with  sulphurous  acid  and  sulphites,  a  pale  yellow 
precipitate;  with  potash,  a  yellow  precipitate  of  hydrated 
rhodic  oxide,  soluble  in  excess ;  with  ammonia,  a  yellow  pre- 
cipitate of  rhodate  of  ammonia,  which,  however,  does  not  form 
immediately;  with  alkaline  carbonates,  a  yellow  precipitate 
after  a  while.  Iodide  of  potassium  produces  a  slight  yellow 
precipitate ;  protochloride  of  tin  imparts  a  dark  colour  to  the 
solutions,  but  forms  no  precipitate.  Acetate  of  lead,  mercu- 
rous  nitrate,  and  nitrate  of  silver  form  precipitates  analogous 
in  composition  to  the  iridium-salts  already  mentioned  (p.  397). 
Zinc  precipitates  metallic  rhodium.  In  a  solution  of  rhodium 
mixed  with  excess  of  potash,  alcohol  forms,  even  at  ordinary 
temperatures,  a  black  precipitate,  probably  consisting  of  me- 
tallic rhodium ;  with  the  other  platinum-metals,  this  reaction 
takes  place  only  when  the  liquid  is  heated.  No  precipitate 
is  formed  by  phosphate  of  soda,  sal-ammoniac,  chloride  of 
potassium,  chromate  of  potash,  oxalic  acid,  cyanide  of  potas- 
sium, cyanide  of  mercury,  ferrocyanide  or  ferricyanide  of 
potassium,  or  gallic  acid.  Hydrogen  gas  reduces  the  anhy- 
drous salts  at  a  moderate  heat. 

Sulphide  of  rhodium. —  Rhodium  may  be  united  with  sul- 
phur by  either  the  dry  or  the  humid  way.     The  sulphide  of 


410  RHODIUM. 

rhodium  was  used  by  Wollaston  to  obtain  the  metal  in  a 
coherent  mass. 

Protochloride  of  rhodium^  RCl,  is  obtained  by  heating  the 
protosulphate  (precipitated  from  rhodic  salts  by  hydrosul- 
phuric  acid)  in  a  stream  of  chlorine ;  or  by  digesting  one  of 
the  intermediate  oxides  with  hydrochloric  acid,  whereupon 
the  sesquichloride  dissolves,  and  the  protochloride  remains  in 
the  form  of  a  reddish  grey  powder  insoluble  in  water. 

Sesquichloride  of  rhodium,  R2CI3,  is  obtained  from  the 
double  chloride  of  rhodium  and  potassium,  by  precipitating 
the  latter  metal  with  fluosilicic  acid.  The  dry  salt  thus 
obtained  is  brown  black,  and  not  crystalline;  it  requires  a 
pretty  high  tempcratui'c  to  decompose  it,  and  then  resolves 
itself  at  once  into  clilorine  and  rhodium.  This  salt  deliquesces 
in  air ;  its  solution  in  water  is  of  a  beautiful  red  colour  (Ber- 
zelius).  Sesquichloride  of  rhodium  is  also  obtained  in  the 
form  of  a  rose-red  powder  by  heating  the  metal  to  low  redness 
in  a  stream  of  chlorine  (Clans) .  This  red  powder,  which  was 
regarded  by  Berzelius  as  R2CI3  .  211C1,  is  slowly  decomposed 
when  heated  in  hydrogen  gas,  is  insoluble  in  strong  hydro- 
chloric and  aqua-rcgia  even  at  the  boiling  heat,  is  coloured 
yellow  by  continued  boiling  with  potash,  and  if  afterwards 
boiled  with  strong  hydrochloric  acid,  dissolves  in  small  quan- 
tity, forming  a  rosc-colom'cd  solution,  the  greater  part,  how- 
ever, remaining  unaltered. 

A  chloride  of  rhodium  and  potassium,  containing  2KCl.R2d3 
+  2H0,  is  obtained  by  the  action  of  chlorine  on  a  mixture  of 
rhodium  and  chloride  of  potassium,  or  by  evaporating  a  solution 
of  the  sesquichloride  of  rhodium  and  sodium  with  chloride  of 
potassium.  It  forms  brown,  doubly  oblique  prisms,  which 
dissolve  sparingly  in  water.  Another  double  salt,  containing 
3KC1 .  R2CI3  +  6II0,  is  obtained  in  dark  red,  sparingly 
soluble,  efflorescent  prisms,  by  spontaneous  evaporation  of 
a  solution  of  the  hydratcd  sesquioxide  in  hydrochloric  acid 
mixed  with  chloride  of  potassium.      The  sodium  double-salt, 


ESTIMATION    OF    RHODIUM.  411 

3NaCl .  ^2^13  +  24HO,  forms  doubly  oblique  prisms  of  a 
deep  cherry-red  colour.  With  chloride  of  ammonium,  two 
double  salts  are  obtained,  viz.,  2NH4CI .  ^2^\  +  2H0,  and 
3NH4CI .  R2CI3  +  3H0,  both  of  which  form  red  prismatic 
crystals.  By  precipitating  either  of  the  above  double  chlorides 
containing  2  or  3  eq.  of  the  basic  chloride  to  1  eq.  R2CI3, 
with  acetate  of  lead,  mercurous  nitrate,  or  nitrate  of  silver, 
rose-coloured  precipitates  are  formed,  containing  2  or  3  eq.  of 
PbCl,  Hg2Cl,  or  AgCl,  to  1  eq.  of  R^Clg  (Claus). 

A  sulphate  of  rhodium  is  formed  when  rhodium  is  ignited 
with  bisulphate  of  potash ;  it  gives  a  yellow  solution.  Another 
sulphate  in  combination  with  sulphate  of  potash  gradually 
falls  as  a  white  powder,  when  sulphuric  acid  is  added  to  a 
solution  of  the  double  chloride  of  these  bases.  It  is  nearly 
insoluble  in  water;  its  formula  is  KO .  SO^  +  203-3^03. 
Nitrate  of  rhodium  is  formed  by  dissolving  the  oxide  in  nitric 
acid.  It  forms  a  deliquescent  salt  of  a  dark  red  colour, 
II2O3  •  3NO5 ;  the  last  salt  combines  with  nitrate  of  soda, 
forming  dark  red  crystals  soluble  in  water  but  not  in  alcohol  : 
NaO  .  NO5  +  R2O3  •  3NO5. 

The  salts  of  rhodium  are  often  mixed  with  peculiar  rose- 
coloured  salts,  whose  nature  is  not  exactly  known.  These 
new  salts  are  not  precipitated,  either  by  iodide  of  potassium 
in  the  cold,  or  by  sulphurous  acid,  or  by  ammonia ;  they  form, 
with  chloride  of  ammonium,  double  salts,  which  crystallise, 
not  in  scales,  but  in  red  prisms  (Fremy). 


ESTIMATION    AND    SEPARATION    OF    RHODIUM. 

Rhodium  is  estimated  in  the  metallic  state.  The  solution 
containing  it  is  mixed  with  excess  of  carbonate  of  soda  and 
evaporated  to  dryness,  the  residue  ignited,  and  the  calcined 
mass  treated  with  cold  water  :  oxide  of  rhodium  then  remains, 
and  may  be  reduced  by  hydrogen. 

VOL.  II.  F   F 

4^' 


4 


412  RHODIUM. 

Rhodium  is  separated  from  many  metals  with  which  it  may 
be  alloyed,  by  fusing  the  alloy  with  bisulphate  of  potash ; 
the  rhodium  is  thereby  converted  into  sulphate  of  rhodium 
and  potassium,  which  may  be  dissolved  out  by  water.  The 
method  of  separating  it  from  platinum  and  the  allied  metals 
has  already  been  given. 

The  separation  of  rhodium  from  other  metals  in  solution  is 
somewhat  difficult,  because  it  is  not  completely  precipitated 
by  hydrosulphuric  acid.  To  separate  rhodium  from  copper , 
the  solution  is  saturated  with  hydrosulphuric  acid  and  left  to 
stand  in  a  stoppered  bottle  for  twelve  hours,  then  filtered,  and 
the  filtrate  heated  to  separate  an  additional  portion  of  sulphide 
of  rhodium.  The  whole  of  the  precipitate  is  then  roasted  in 
a  platinum  crucible  till  the  sulphides  are  completely  oxidised, 
and  the  product  treated  with  strong  hydrochloric  acid,  which 
dissolves  the  copper  and  leaves  the  oxide  of  rhodium.  The 
liquid  filtered  from  the  hydrosulphuric  acid  precipitate  still 
contains  a  small  portion  of  rhodium,  which  may  be  precipi- 
tated by  carbonate  of  soda  and  converted  into  oxide  as  above. 
The  whole  of  the  oxide  is  then  reduced  by  hydrogen. 

To  separate  rhodium  from  iron,  the  rhodium  is  precipitated 
as  completely  as  possible  by  hydrosulphuric  acid ;  the  liquid 
filtered ;  and  the  iron  in  the  filtrate  precipitated  by  ammonia, 
after  having  been  brought  to  the  state  of  sesquioxide.  The 
iron-precipitate  carries  down  with  it  a  certain  portion  of  rho- 
dium, which  may  be  separated  by  igniting  the  precipitate  in 
a  current  of  hydrogen,  and  treating  the  reduced  metals  with 
hydrochloric  acid,  which  dissolves  the  iron  and  leaves  the 
rhodium  :  the  latter  is  then  converted  into  oxide  by  ignition 
in  the  air.  The  precipitated  sulphide  of  rhodium  is  likewise 
oxidised  by  roasting.  The  small  quantity  of  rhodium  which 
remains  in  solution  after  precipitation  by  ammonia  is  preci- 
pitated by  carbonate  of  soda,  and  converted  into  oxide  by 
ignition.  The  whole  of  the  oxide  of  rhodium  is  then  reduced 
to  the  metallic  state  by  hydrogen. 


RUTHENIUM.  413 

The  separation  of  rhodium  from  the  alkali-metals  is  easily- 
effected  by  converting  the  metals  into  chlorides,  and  igniting 
the  chlorides  in  a  current  of  hydrogen,  which  reduces  only 
the  chloride  of  rhodium. 


SECTION   YI. 

RUTHENIUM. 

:E.q,  52'1  or  651-25  ;  Ru. 

This  metal  was  discovered  hy  Clans  in  1846.  It  occurs 
in  platinum  ores,  chiefly  in  the  native  osmide  of  iridium, 
which  contains  from  3  to  6  per  cent,  of  it.  To  separate  it, 
the  osmide  of  iridium  is  pulverised,  mixed  with  about  half  its 
weight  of  common  salt,  and  heated  to  low  redness  in  a  current 
of  moist  chlorine  gas.  The  disintegrated  mass  is  then  digested 
in  cold  water,  and  the  concentrated  solution,  which  is  brown- 
red  and  almost  opaque,  mixed  with  a  few  drops  of  ammonia 
and  gently  heated,  whereupon  it  deposits  a  copious  black- 
brown  precipitate,  consisting  of  sesquioxide  of  ruthenium 
and  bioxide  of  osmium.  This  precipitate,  after  being  washed 
with  nitric  acid,  is  heated  in  a  retort,  till  the  osmium  is  ex- 
pelled in  the  form  of  osmic  acid.  The  residue  is  then  ignited 
for  an  hour  in  a  silver  crucible  with  caustic  potash  free  from 
silica,  and  the  ignited  mass  softened  and  dissolved  by  cold 
distilled  water.  The  solution  is  left  in  a  corked  bottle  for  two 
hours  to  clarify ;  after  which  the  perfectly  transparent  orange- 
coloured  liquid  is  separated  by  a  siphon,  and  neutralised  with 
nitric  acid.  It  then  deposits  velvet-black  sesquioxide  of 
ruthenium,  which,  when  washed,  dried,  and  ignited  in  an 
atmosphere  of  hydrogen,  yields  the  pure  metal. 

Ruthenium  is  a  grey  metal,  very  much  Hke  iridium.     Its 

FP  2 


414  RUTHENIUM. 

specific  gravity  is  8'6.  *  It  is  very  brittle,  does  not  fuse  even 
in  the  flame  of  the  oxy-hydrogen  blowpipe,  and  is  scarcely 
attacked  by  aqua-regia.  It  combines  with  oxygen  in  four 
proportions,  forming  the  three  oxides,  RuO,  RU2O3,  KuOj, 
and  ruthenic  acid,  RUO3.  Its  affinity  for  oxygen  is  greater 
than  that  of  any  of  the  other  platinum  metals,  except  osmium. 
When  heated  to  redness  in  the  air,  it  oxidises  readily,  forming 
a  ]3luish  black  oxide,  which  does  not  part  with  its  oxygen  at  a 
white  heat.  When  fused  with  nitre  or  with  caustic  potash,  it 
is  converted  into  rutheniate  of  potash.  It  is  not  dissolved 
by  fused  bisulphate  of  potash. 

Protoxide  of  ruthenium,  RuO. — Obtained  by  igniting  the 
protochloride  with  carbonate  of  soda,  in  a  stream  of  carbonic 
acid  gas,  and  washing  the  residue  with  water.  It  is  a  blackish 
grey  powder,  containing  13*4  per  cent,  of  oxygen.  It  is  in- 
soluble in  acids,  and  consequently  its  salts  have  not  been 
directly  formed. 

The  p7'otochloride,  RuCl,  is  obtained  in  the  anhydrous 
state,  by  heating  the  metal  to  low  redness  in  a  stream  of 
chlorine.  It  is  a  black  crystalline  substance,  insoluble  in 
water  and  acids,  and  imperfectly  decomposed  by  alkalies.  A 
soluble  pix)tochloride  appears,  however,  to  be  formed  by 
passing  hydrosulphuric  acid  gas  through  a  solution  of  the 
sesquicldoride. 

Sesquioxide  of  rutJienium,  Ru^^Og. — Pulverulent  ruthenium, 
strongly  heated  before  a  powerful  blowpipe  turns  black,  and 
rapidly  absorbs  oxygen,  100  parts  of  the  metal  increasing  to 
118  parts;  afterwards  the  oxidation  slowly  proceeds  further 
till  the  oxide  acquires  a  blackish  blue  colour,  and  contains  23 
or  24  parts  of  oxygen  to  100  parts  of  metal,  which  is  about 
the  proportion  required  for  the  sesquioxide.     The  hydrated 


*  This  is  much  less  than  the  density  usually  attributed  to  iridium  (p.  395.)' 
It  is  probable,  however,  that  the  two  metals  do  not  really  differ  much  in 
density ;  for  a  specimen  of  porous  iridium  prepared  from  the  blue  oxide,  by 
reduction  with  hydrogen,  exliibitcd  a  density  of  only  9"3  (Claus). 


SESQUIOXIDE    OF    RUTHENIUM.  415 

sesqmoxide  is  formed  by  precipitating  a  solution  of  the 
sesquichloride  with  an  alkali,  by  decomposing  a  solution  of 
rutheniate  of  potash  with  nitric  acid,  or  by  heating  the 
aqueous  solution  of  the  sesquichloride.  It  is  a  black-brown 
powder,  which  becomes  suddenly  incandescent  when  heated. 
Hydrogen  gas  reduces  it  imperfectly  at  ordinary  temperatures. 
It  is  insoluble  in  alkalies,  but  dissolves  in  acids,  forming 
orange-yellow  solutions.  The  solution  in  hydrochloric  acid 
exhibits  the  following  reactions : — Hydrosulphuric  acid  partly 
precipitates  the  ruthenium  in  the  form  of  a  black  sulphide, 
but  at  the  same  time  reduces  the  sesquichloride  to  proto- 
chloride,  the  reduction  being  attended  with  a  change  of  colour 
from  orange-yellow  to  a  fine  azure  blue  :  this  reaction  is  ex- 
tremely delicate,  and  very  characteristic  of  ruthenium.  Zinc 
effects  the  same  reduction.  Hydrosulphate  of  ammonia  throws 
down  the  greater  part  of  the  ruthenium  in  the  form  of  a  black- 
brown  sulphide,  not  perceptibly  soluble  in  excess.  The  caustic 
alkalies  J  alkaline  carbonates ,  and  phosphate  of  soda  precipitate 
the  black  sesquioxide,  insoluble  in  excess  of  the  reagent. 
Borax  forms  no  precipitate  at  first,  but,  on  heating  the  solu- 
tion, the  hydrated  sesquioxide  is  thrown  down.  Sulphurous 
acid,  oxalic  acid,  and  formiate  of  soda  do  not  precipitate  the 
metal,  but  merely  decolorise  the  solution.  Ferrocyanide  of 
potassium  decolorises  the  solution  at  first,  but  afterwards  turns 
it  bluish  green.  Acetate  of  lead  forms  a  purple-red  precipi- 
tate, inclining  to  black.  Cyanide  of  mercury  colours  the 
solution  blue,  and  throws  down  a  blue  precipitate.  Nitrate 
of  silver  forms  a  black  precipitate,  which  is  a  mLxture  of 
chloride  of  silver  and  sesquioxide  of  ruthenium ;  the  oxide 
dissolves,  after  a  while,  in  the  nitric  acid,  leaving  a  white 
residue  of  chloride  of  silver ;  and,  if  ammonia  be  then  added 
in  excess,  the  chloride  of  silver  dissolves,  and  the  sesquioxide 
of  ruthenium  is  reprecipitated :  this  is  also  a  very  delicate 
reaction.  The  chlorides  of  potassium  and  ammo)iium  throw 
down  from   concentrated    solutions,    crystalline   precipitates 


416  RUTHENIUM. 

of  double  chlorides,  exhibiting  a  play  of  colorirs  inclining  to 
violet. 

Sesquichloride  of  ruthenium,  Itu2Cl3,  is  obtained  in  the  solid 
state  by  evaporating  the  solution  of  the  sesquioxide  in  hydro- 
chloric acid.  The  residue  is  deliquescent,  has  a  very  astringent 
but  not  metallic  taste,  and  dissolves  in  water  and  alcohol, 
forming  beautiful  orange-coloured  solutions,  but  leaving  a 
yellow  basic  compound  undissolved.  When  heated,  it  turns 
green  and  blue.  The  dilute  solution  is  resolved  by  heat  into 
hydrochloric  acid  and  the  hydrated sesquioxide  (pp.414,  415). 
The  sesquichloride  forms  double  salts  with  the  chlorides  of 
potassium  and  ammonium,  and  apparently  also  with  those  of 
sodium  and  barium. 

Bioxide  of  rutheniumy  Ruthenic  oxide,  RuOj,  is  formed  by 
roasting  and  igniting  the  bisulphide,  or  by  strongly  igniting 
the  sulphate,  RuOj  .  2SO3  ;  the  former  method  yields  a  black- 
blue  powder,  with  a  tinge  of  green ;  the  latter,  grey  particles 
with  metallic  lustre  and  bluish  or  greenish  iridescence.  The 
hydrate,  RuOj .  2H0,  is  obtained  as  a  gelatinous  precipitate 
by  decomposing  the  bichloride  of  ruthenium  and  potassium 
with  carbonate  of  soda.  The  precipitate,  when  dried  and 
heated  in  a  platinum  spoon,  deflagrates  with  vivid  incan- 
descence, and  is  scattered  about.  It  dissolves  in  acids, 
forming  solutions  which  are  yellow  when  dilute  and  rose- 
coloured  when  concentrated. 

The  bichloride  is  not  known  in  the  separate  state,  but 
forms  with  chloride  of  potassium  a  double  salt,  KCl,RuCl2, 
which  is  obtained  by  treating  the  sesquichloride  of  ruthenium 
and  potassium  with  aqua-regia.  This  double  salt  is  very 
soluble  in  water,  but  insoluble  in  alcohol ;  its  colour  is  brown 
inclining  to  rose-red.  The  aqueous  solution  has  a  deep  rose- 
colour,  strongly  resembling  that  of  sesquichloride  of  rhodium. 
Hydrosulphuric  acid  acts  but  slowly  on  this  solution,  pro- 
ducing first  a  milky  turbidity  from  precipitated  sulphur,  and 
afterwards  throwing  doAvn  a  yellowish  brown  sulphide ;  the 


RUTHENIC    ACID.  417 

solution,  however,  still  retains  a  deep  rose-colour  and  does  not 
turn  blue. 

Ruthenic  sulphate,  RuOg.SSOg.  —  When  the  sulphide  ob- 
tained by  treating  the  sesquichloride  with  hydrosulphuric  acid 
is  digested  in  moderately  strong  nitric  acid,  an  orange-yellow 
solution  is  formed,  which,  on  evaporation,  yields  this  salt  in 
the  form  of  a  yellowish  brown  amorphous  mass.  It  is  deli- 
quescent, and  dissolves  readily  in  water.  Alkalies  added  to 
the  solution  form  no  precipitate  at  first ;  but,  on  evaporating, 
a  yellowish  brown  gelatinous  precipitate  is  obtained,  consist- 
ing of  hydrated  ruthenic  oxide,  and  strongly  resembling 
impure  rhodic  oxide.  The  solution  of  this  salt  does  not  turn 
blue  when  treated  with  hydrosulphuric  acid. 

Ruthenic  acid,  E-uOg,  is  known  only  in  the  form  of  a  potash- 
salt,  which  is  obtained  by  igniting  ruthenium  with  a  mixture 
of  potash  and  nitrate  or  chlorate  of  potash.  It  dissolves  in 
water,  forming  an  orange-yellow  solution,  which  has  an  astrin- 
gent taste,  colours  organic  substances  black  by  coating  them 
with  oxide,  and  is  decomposed  by  acids,  yielding  a  precipitate 
of  the  sesquioxide. 

Sulphides  of  ruthenium.  —  This  metal  probably  forms  with 
sulphur  a  series  of  compounds  analogous  to  the  oxides ;  but  it 
is  difficult  to  obtain  them  in  a  definite  state.  Sulphur  and 
ruthenium  do  not  combine  directly,  and  the  precipitates 
thrown  down  by  hydrosulphuric  acid  from  the  chlorides 
always  contain  excess  of  sulphur.  When  the  sulphide  ob- 
tained by  precipitation  from  the  sesquichloride  is  heated  in 
an  atmosphere  of  carbonic  acid,  incandescence  and  explosion 
take  place,  sulphur  and  water  pass  ofi^,  and  a  blackish  grey 
metallic  powder  is  left,  whose  analysis  agrees  with  the  formula 
IIU2S3.  All  the  sulphides  are  dissolved  by  nitric  acid  of 
ordinary  strength    (Claus). 


L-' 


418  RUTHENIUM, 


ESTIMATION    AND    SEPARATION    OF    RUTHENIUM. 

This  metal  is  precipitated  from  its  solutions  in  the  form  of 
oxide,  and  generally  as  sesquioxide,  viz.  from  a  solution  of 
the  sesquichloridej  either  by  alkalies  or  by  simply  heating  the 
solution,  and  from  a  solution  of  riithcniate  of  potash  by  nitric 
acid.  The  precipitated  oxide  is  reduced  to  the  metallic  state 
by  ignition  in  an  atmosphere  of  hydrogen.  As,  however,  the 
precipitate  generally  contains  alkali,  which  cannot  be  removed 
by  washing,  the  reduced  mass  must  be  treated  with  water ; 
the  liquid  filtered  from  the  ruthenium ;  and  the  metal,  be- 
fore weighing,  must  be  again  ignited  and  left  to  cool  in  an 
atmosphere  of  hydrogen,  as  it  oxidises  when  heated  in  the 
air.  Ruthenium  has  hitherto  been  found  only  associated 
with  the  metals  of  the  platinum-residues,  and  from  these  it  is 
separated  by  the  method  described  at  page  413.,  depending 
on  the  resolution  of  the  aqueous  scsquichloride  by  heat  into 
hydrochloric  acid  and  sesquioxide  of  ruthenium. 


NEW    METHOD    OF    TREATING    PLATINUM-RESIDUES.* 

When  platinum-ore  has  been  exhausted  by  aqua-regia,  a 
residue  is  left,  commonly  known  by  the  name  of  osmide  of 
iridium.  This  residue  is  a  mixture  of  two  different  sub- 
stances, one  of  which  is  scaly,  and  consists  of  osmium,  iridium, 
and  ruthenium ;  while  the  other,  which  is  granular,  contains 
but  mere  traces  of  osmium  and  ruthenium,  but  is  very  rich 
in  iridium  and  rhodium.  Now  oxide  of  ruthenium  can  bear 
a  red  heat  without  decomposing,  and  osmium  is  actually 
roasted  by  the  action  of  oxygen,  producing  a  volatile  acid, 
just  as  sulphur  and  arsenic  do;  hence  the  residue  of  platinum- 
ore  may  be  decomposed  by  roasting ;  and  by  submitting  it  to 

*  Fremy,  Compt.  rend,  xxxviii.  1008  ;  also  Traits  do  Chimie  Generale,  par 
Pelouze  et  Fremv,  iii.  452. 


TREATMENT    OF    PLATINUM-RESIDUES.  419 

this  operation,  osmic  acid  is  produced  in  large  quantity  and 
very  pure,  and  oxide  of  ruthenium  is  obtained  in  well-defined 
crystals.     The  roasting  is  performed  as  follows  : — 

About  200  grammes  of  platinum-residue  (the  scaly  and 
granular  alloys  together)  are  heated  to  bright  redness  in  a 
porcelain  tube  placed  in  a  long  furnace.  Air  is  drawn  through 
the  tube  by  means  of  an  aspirator,  being  first  made  to  pass 
through  solution  of  potash  to  free  it  from  carbonic  acid,  and 
through  strong  sulphuric  acid  to  remove  organic  matter.  The 
air  thus  purified  passes  over  the  heated  platinum-residue,  and 
forms  osmic  acid  and  oxide  of  ruthenium.  The  latter  crystal- 
lises in  the  colder  parts  of  the  roasting  tube,  while  the  more 
volatile  osmic  acid  is  carried  forward,  first  into  a  series  of 
empty  tubes,  in  which  part  of  it  settles  in  the  form  of  crys- 
tals, and  then  through  two  bottles  filled  with  solution  of 
potash,  which  retains  the  uncondensed  vapours :  the  apparatus 
terminates  with  an  aspirator.  The  products  of  the  operation 
are : — 1.  Oxide  of  ruthenium,  in  violet  crystals,  the  form  of 
which  is  similar  to  that  of  native  oxide  of  iron ;  2.  Osmic 
acid,  very  pure,  and  sometimes  amounting  to  40  per  cent,  of 
the  platinum-residue  used ;  3.  Osmiate  of  potash,  which,  by 
the  addition  of  a  few  drops  of  alcohol,  may  be  converted  into 
osmite  of  potash,  a  salt  from  which  metallic  osmium  may  be 
obtained  (p.  403) ;  4.  An  alloy  of  iridium  and  rhodium,  which 
remains  in  the  roasting  tube. 

This  last  residue  may  be  used  for  the  preparation  of  iridium 
and  rhodium.  For  this  purpose,  it  is  calcined  in  an  earthen 
crucible  with  four  times  its  weight  of  nitre,  care  being  taken 
not  to  carry  the  process  too  far ;  and  the  residue  is  exhausted 
with  boiling  water  and  filtered.  A  copious  precipitate  is 
thereby  formed,  which  remains  on  the  filter,  and  the  filtrate 
consists  of  an  alkaline  liquid,  which,  when  left  to  evaporate, 
deposits  crystals  of  osmite  of  potash,  the  osmium  never  being 
completely  removed  by  the  previous  roasting. 

The  precipitate  which  remains  on  the  filter  and  retains  a 

VOL.  II.  G  G 


420  PLATINUM-RESIDUES. 

considerable  quantity  of  potash,  is  subjected  to  the  action  of 
aqua-regia,  which  converts  the  iridium  into  chloriridiate  of 
potassium,  nearly  insoluble  in  cold  water :  the  action  of  the 
aqua-regia  must  be  continued  for  several  hours.  The  mass  is 
then  treated  with  boiling  water,  which  dissolves  the  chlor- 
iridiate of  potassium,  the  washing  being  continued  tiU  the 
extract  no  longer  exhibits  a  brown  colour.  The  solutions  are 
then  evaporated,  and  the  chloriridiate  of  potassium  obtained 
in  crystals. 

The  undissolved  portion,  which  contains  the  rhodium,  is 
dried,  mixed  with  an  equal  weight  of  chloride  of  sodium,  and 
subjected  for  three  or  four  hours  to  the  action  of  dry  chlorine 
at  a  dull  red  heat.  Chlororhodiate  of  sodium  is  thereby 
formed,  and  may  be  obtained,  by  solution  in  water  and 
evaporation,  in  beautiful  rose-coloured  octohedral  crystals, 
resembling  chrome-alum. 

Rhodium  is  likewise  obtained  in  another  stage  of  the  treat- 
ment of  platinum-ore.  When  this  ore  is  treated  with  aqua- 
regia  a  certain  quantity  of  rhodium  is  dissolved  together  with 
the  platinum,  althougli  rhodium  by  itself  is  insoluble  in  aqua- 
regia.  The  solution  is  evaporated  to  drj^ness,  the  residue 
dissolved  in  water,  and  the  solution  mixed  with  sal-ammoniac 
to  precipitate  the  platinum.  The  rhodium  then  remains  in 
solution,  together  with  a  small  quantity  of  platinum,  to  sepa- 
rate which  a  plate  of  iron  is  immersed  in  the  liquid,  and  the 
pulverulent  mixture  of  platinum  and  rhodium  thereby  pre- 
cipitated is  digested  in  weak  aqua-regia,  which  dissolves  the 
platinum  and  leaves  the  rhodium  nearly  pure.  From  this 
residue,  pure  well-defined  crystals  of  chlororhodiate  of  sodium 
may  be  obtained  in  the  manner  just  described  (Fremy). 


SUPPLEMENT. 


HEAT 


EXPANSION   OF    SOLIDS. 


The  following  determinations  of  the  amount  of  the  cubical 
expansion  of  solids  for  each  degree  Centigrade,  at  tempera- 
tures not  exceeding  100°  C,  are  given  by  H.  Kopp*,  the 
volume  of  the  solid  at  0°  being  taken  equal  to  1 :  — 


Table  I.  —  Cubical  Expansion  of  Solids. 


Cubical 

Cubical 

Substance. 

Formula. 

Exp.  for 
PC 

Substance. 

Formula. 

Exp.  for 

lOC. 

Copper 

Cu 

0-000051 

Arragonite  . 

CaO.CO, 

0000065 

Lead    . 

Pb 

0-000089 

Calcspar 

CaO.CO, 

0-000018 

Tin      . 
Iron     . 

Sn 
Fe 

0-000069 
0-000037 

Bitterspar    . 

{ 

CaO.CO^       -1 
+  MgO.CO,      J 

0-000035 

Zinc     . 
Cadmium     . 

Zn 
Cd 

0-000089 
0-000094 

Iron- spar     . 

Fe(Mn,Mg)0.  "1 
C02           J 

0-000035 

Bismuth 

Bi 

0-000040 

i  Heavy  spar . 

BaO.SOg 

0-000058 

Antimony    . 

Sb 

0-000033 

Coelestin 

SrCSOg 

0-000061 

Sulphur 

s 

0-000183 

Quartz 

Si03           { 

0-000042 

Galena 

PbS 

0000068 

0-000039 

Zinc-blende 

ZnS 

0-000036 

Orthoclase  . 

KO.SiOg       1 
+  A1.^03.3Si03  J 

0000026 

Iron  pyrites 

EeS^ 

0-000034 

0-000017 

Rutilc  . 

TiO^ 

0-000032 

Soft     soda 

Tin  stone     . 

SnO„ 

0-000016 

glass 

. 

0-000026 

Iron-glance . 

Fe,03 

0000040 

Another  sort 

. 

0-000024 

Magnetic  iron 

Hard  potash 

ore    . 

FCgO^ 

0-000029 

glass 

.          . 

0-000021 

Fluor-spar  . 

CaF 

0-000062 

VOL.  II. 


*  Ann.  Ch.  Pharm.  Ixxxi. 
II  II 


422  EXPANSION    OF    SOLIDS. 

The  mode  of  experimenting  consisted  in  taking  the  specific 
gravity  of  the  solid  substance  at  a  lower  and  at  a  higher 
temperature,  by  ascertaining  the  quantity  of  water  together 
with  a  known  weight  of  the  solid  substance,  and  also  the 
quantity  of  water  alone,  which  filled  a  vessel  of  constant 
capacity  at  the  different  temperatures.  The  determinations 
in  the  instances  of  iron  and  glass,  and  the  second  determina- 
tions of  quartz  and  orthoclase,  were  made  with  mercury  in- 
stead of  water,  and  calculated  in  a  similar  manner. 

Kopp  has  also  determined  the  expansion  of  some  other 
solids,  especially  near  the  melting  points.*  Most  bodies,  at 
temperatures  near  their  melting  points,  exhibit  a  sudden 
increase  in  the  rate  of  expansion.  The  increase  of  volume 
which  a  substance  exhibits  in  the  fused  state,  as  compared 
with  the  same  substance  at  lower  temperatures,  arises,  partly 
from  the  great  expansion  which  it  undergoes  as  it  approaches 
the  melting  point,  partly  from  the  sudden  expansion  which 
takes  place  in  fusing.  In  some  substances,  however,  only 
one  of  these  modes  of  expansion  is  at  all  considerable. 

FhospJioriis  (the  yellow  modification),  of  sp.  gr.  1*826  at 
10°  C.  (50°  F.),  expands  uniformly  up  to  its  melting  point 
44°  C.  (111*2°  F.),  at  which  temperature  its  volume  is  1*017 
of  the  volume  at  0°  C. ;  but,  at  the  moment  of  fusion,  it  ex- 
hibits a  sudden  expansion  amounting  to  3*4  per  cent.,  so  that 
its  liquid  volume  at  44°  C.  is  1-052. 

Sulphur  (native  crystals,  sp.  gr.  2-069)  expands  irregularly 
near  its  melting  point  (115°  C.  or  239°  F.).  Its  volume  being 
latO°C.,isl-010at50°C.(122°F.);  1*037  at  100°  C;  1-096 
at  115°  C;  at  the  moment  of  fusion,  the  expansion  amounts 
to  5  per  cent.,  the  volume  then  increasing  to  1*150. 

Wa.v  (bleached  beeswax,  sp.  gr.  0-976  at  10°  C.)  expands 
very  rapidly  as  it  approaches   its   melting  point  (64°  C.  or 

*  Ann.  Ch.  Pharm.  xciii.  129. 


EXPANSION   OF   LIQUIDS.  423 

147*2°  F.),  but  only  0*4  per  cent,  more  at  the  moment  of  fusion. 
If  the  volume  at  0°  C.  is  1,  the  volume  at  50°  C.  (122°  F.) 
is  1-068  ;  at  60°  C.  (14*0°  F.)  is  1-128  ;  at  64°  C.  (147-2°  F.) 
is  1*161,  and  increases  bj  fusion  to  1-166. 

Water  expands  at  the  moment  of  freezing  by  about  10  per 
cent.  1-1  volume  of  ice  gives  1  volume  of  water  at  0°  C, 
which,  when  heated  to  4°  C.  (39*2°  F.),  contracts  to  0-99988, 
but  expands  progressively  at  higher  temperatures,  its  volume 
at  100°  being  1-043. 

Solid  hydrated  salts,  on  the  contrary,  expand  at  the  moment 
of  fusion;  e.  g,  chloride  of  calcium  (CaCl  +  6H0),  by  9*6  per 
cent. ;  ordinary  phosphate  of  soda  (2NaO.HO.P05+  24HO) 
and  hyposulphite  of  soda  (NaOSgOg  +  5H0),  each  by  5*1 
per  cent. 

Roses  fusible  metal  (2  parts  bismuth,  1  part  tin,  and  1  part 
lead,  sp.  gr.  8*906  at  10°  0.)  expands,  when  heated  from  0°"to 
59°  C.  (32°  to  138*2°  F.),  in  the  ratio  of  1  to  1-0027  ;  but  con- 
tracts when  further  heated,  its  volume  at  82°  C.  (179*6°  F.) 
being  equal  to  that  at  0°  C,  and  at  95°  C.  (203°  F.)  equal  to 
0*9947  ;  in  fusing,  between  95°  and  98°  C,  it  expands  by 
1-55  per  cent.,  so  that  at  98°  C.  (208-4°  F.)  its  volume  is 
equal  to  1*0101.  This  alloy,  therefore,  contracts  from  59°  C. 
up  to  its  melting  point. 


EXPANSION   OF   LIQUIDS. 

M.  Pierre's  researches  on  this  subject  have  been  con- 
tinued.* The  expansions  of  a  great  number  of  liquids  have 
also  been  determined  by  H.  Kopp.  f 


*  Annales  de  Chimie  et  de  Physique,  [3],  xxi.  118,  xxxiii.  119. 
f  Pogg.  Ann.  Ixxii.  1  and  223  ;  and  Ann.  Ch.  Pharm.  xciii.  157  ;  xciv. 
257  ;  xcv.  307  ;  xcviii.  367. 

H  H  2 


424 


EXPANSION   OF   LIQUIDS. 


Pierre  concludes  from  Ins  experiments  that  isomeric  liquids 
in  general  do  not  contract  equally  at  an  equal  number  of 
degrees  below  their  respective  boiling  points;  an  exception  is, 
however,  presented  by  acetate  of  methyl  (CgHgO .  C4H3O3) 
and  formiate  of  ethyl  (C^H^O .  C2HO3),  in  which  the  con- 
traction for  equal  intervals  below  the  boiling  points  appears 
to  be  equal.* 

Table  II.  exhibits  the  contractions  of  several  groups  of 
isomeric  liquids,  at  D°  centigrade  below  the  boiling  point,  as 
determined  by  Pierre  and  by  Kopp. 

Table  IL  —  Expaksion  of  Liquids. 


D. 

Aldehyde. 

Butyric  Acid, 
CsHhO^. 

AceUte  of  Ethyl, 
CbH^O,. 

D. 

Pierre 
(B.  P.  2'iO). 

Cio'so). 

Pierre 
(163°). 

(?««;. 

Pierre 
(74-1°). 

(^Tc?). 

0 

10000 

10000 

10000 

10000 

10000 

10000 

0 

10 

9817 

9830 

9872 

9867 

9846 

9843 

10 

25 

9567 

9596 

9688 

9677 

9629 

9622 

25 

45 

9284 

. 

9453 

9439 

9359 

9352 

45 

60 

9094 

. 

9288 

9271 

9172 

9165 

60 

75 

. 

. 

9128 

9112 

8996 

8988 

75 

110 

• 

• 

8781 

8765 

8633 

• 

110 

D. 

Chloride 
of  Ethy- 
lene, 
C^H,Cl2 
Pierre 
(84-90). 

Mono- 
chlorinated 
Chloride 
of  Ethvl, 
C,H,dl,. 
Pierre 
(64-80).    • 

Mono. 

chlorinater 

Chloride  o! 

Ethylene, 

C4H3CI3. 

Pierre 
{114- 2°). 

Blchlo- 
rinated 
Chloride 
of  Ethyl, 
C4H3CI3. 
Pierre 
(74 -90). 

Formiate  of 

Ethyl, 

CeHfiO^. 

Acetate  of 
Methyl, 
CfiHgO,. 

D. 

Pierre 
(52-90). 

<»,. 

Pierre 

Kopp 
(56  36). 

0 

10000 

10000 

10000 

10000 

10000 

10000 

10000 

10000 

0 

25 

9677 

9669 

9693 

9648 

9632 

9631 

9633 

9631 

25 

55 

9331 

9300 

9350 

9267 

9241 

9243 

9243 

9243 

55 

80 

9068 

9003 

9090 

8988 

8953 

• 

8955 

♦ 

80 

♦  The  contrary  statement  originally  made  by  Pierre,  and  quoted  at  p.  7. 
Vol.  L  of  this  work,  was  founded  on  an  error  of  calculation. 


EXPANSION  OF   LIQUIDS. 


425 


Expansion  of  water.  —  Table  III.  contains  the  results  ob- 
tained by  Kopp*,  and  also  those  of  Pierre  as  calculated  by 
Frankenheimf,  with  regard  to  the  expansion  of  water  between 
0°  and  100°  C,  the  volume  at  zero  being  taken  as  the  unit. 


Table  III.  —  Expansion  of  Water. 


Volumfe. 

Volume. 

Temp. 

Temp. 

Kopp. 

Pierre. 

Kopp. 

Pierre. 

-  1 0°  C. 

1-003758 

19° 

1-001370 

-10 

, 

1-001658 

20 

1-001567 

1-001594 

-  5 

, 

1-000582 

21 

1-001776 

0 

1-000000 

1-000000 

22 

1-001995 

I 

0-999947 

23 

1-002225 

2 

0-999908 

24 

1-002465 

3 

0-999885 

25 

1002715 

1-002708 

4 

0-999877 

30 

1-004064 

1-004071 

5 

0-999883 

0-999890 

35 

1-005697 

1-005677 

6 

0-999903 

40 

1-007531 

1-007512 

7 

0-999938 

45 

1-009541 

1-009563 

8 

0-999986 

50 

1-011766 

1  011815 

9 

1-000048 

55 

1-014100 

1-014360 

10 

1-000124 

1-000148 

60 

1-016590 

1-017118 

11 

1-000213 

65 

1-019302 

1019947 

12 

1-000314 

70 

1-022246 

1022938 

13 

1-000429 

75 

1-025440 

1-026078 

14 

1-000556 

80 

1-028581 

1-029360  ' 

15 

1-000695 

1-000728 

85 

1-031894 

1-032769 

16 

1-000846 

90 

1-035397 

1-036294 

17 

1-001010 

95 

1-039094 

1-039925 

18 

1-001184 

100 

1-042986 

1-043649 

The  maximum  density  Frankenheim  finds,  from  the  same 
data,  to  exist  at  the  temperature  of  3*86°  C.  or  38*95°  F. ; 
Playfair  and  Joule  J  fix  the  point  of  maximum  density  at 
3-945°  C.  or  39*1°  F. ;  Plucker  and  Gessler§,  at  38°  C. 
or  38-8°  F. 


*  Pogg.  Ann.  Ixxii.  223. 
X  PhiL  Mag.  [3],  xxx.  41. 


t  Pogg.  Ann.  Ixxxvi.  451. 
§  Pogg.  Ann.  Ixxxv.  238. 


II  H  3 


426 


SPECIFIC    HEAT. 


Absolute  expansion  of  mercury. —  From  numerous  measure- 
ments of  the  pressures  exerted  by  columns  of  mercury  of 
equal  height  but  different  temperatures,  Regnault*  finds  that 
if  the  volume  of  mercury  at  0°  C.  be  =  1,  the  volume  at  f  of 
the  air-thermometer  is  given  by  the  formula  — 

1  +  0-0001 79007i  +  0-0000000252316  t\ 


Hence,  the  values  in 


Table  IV.  —  Extansion  of  Mercury. 


Temp. 

Volume. 

Temp. 

Volume. 

50° 
100 
150 
200 

1-009013 
1-018153 
1027419 
1036811 

250° 

300 

350 

1046329 
1-055973 
1-065743 

Militzer  has  also  determined  the  absolute  expansion  of 
mercury  by  similar  means,  but  only  at  ordinary  tempera- 
tures, the  temperature  of  the  colder  column  of  mercury 
ranging,  in  his  experiments,  between  2°  and  4°  C,  and  that 
of  the  warmer  column  between  19°  and  23°.  The  mean 
coefficient  of  expansion  for  1°,  deduced  from  these  experi- 
ments, is  0-00017405  +  0-00000082.t  The  experiments  of 
Dulong  and  Petit  (i.  8.)  give  for  1°  the  coefficient  0-00018018. 


*  "  Relations  des  Experiences  cntreprises,  pour  dct.rrainer  les  princi- 
pales  lois  physiques  ct  les  donnees  numeriques  qui  entrent  dans  le  calcul  des 
machines  a  vapcur."     Paris,  1847. 

f  Pogg.  Ann.  Lxxx   55. 


SPECIFIC    HEAT. 


427 


SPECIFIC   HEAT. 


The  specific  heat  of  most  bodies  is  greater  in  the  liquid 
than  in  the  solid  state.  The  following  determinations  are  by 
Regnault ;  — 


Table  V.  —  Specific  Heat. 


Solid. 

Liquid. 

Substance. 

Temperature. 

Sp.  Heat. 

Temperature. 

Sp.  Heat. 

Lead  . 

0°  to     100°  C. 

0-0314 

350°  to     450°  C. 

00402 

Bromine     . 

-78     „    -20 

0-08432 

10     „       48 

0-1109 

Iodine 

0     „     100 

0-05412 

0-10822 

Mercury     . 

-78     „   -40 

0-0247 

0     „      100 

0-0333 

Sulphur 

0     „     100 

0-2026 

120     „     150 

0-234 

Bismuth     . 

0     „     100 

0-03084 

280     „     380 

0-0363 

Zinc  . 

0     „      100 

0-0956 

Tin    . 

0     „     100 

00562 

250     „     350 

0-0637 

Phosphorus 

10     „       30 

0-1887 

50     „      100 

0-2120 

Amorphous 

15     „       98 

0-1700 

Water 

below     0 

0-502 

0     „       20 

1-0000 

Crystallised  chlo- 

ride of  calcium 

below     0 

0-345 

33     „       80 

0-555 

Nitrate  of  soda   . 

0    to    100 

0-27821 

320     „     430 

0-413 

Nitrate  of  potash 

0     „     100 

0-23875 

350     „     435 

0-3319 

Table  YI.  exhibits  the  specific  heats  of  several  liquids  as 
determined  by  H.  Kopp*,  and  by  Favre  and  Silbermann.f 
The  second  column  shows  the  intervals  of  temperature  in 
Kopp's  determinations.  Those  of  Favre  and  Silbermann 
were  made  by  cooling  the  liquids  in  a  mercurial  calorimeter 
of  peculiar  construction,  from  their  several  boiling  points 
to  temperatures  nearly  equal  to  that  of  the  surrounding 
atmosphere. 


*  Pogg.  Ann.  Ixxv.  98. 

t  Comptes  Rendus,  xxiii.  524. 

HH  4 


428 


SPECIFIC    HEAT. 


Table  VI.  —  Specific  Heat. 


Liquids. 

Temperature. 

Sp.  Heat. 

Observers. 

Mercury 

440  to  24°C. 

0.0332 

Kopp. 

Iodine    .... 

. 

0-10822 

F.  S. 

Bromine 

45     „    11 

0.107 

Andrews. 

Sulphuric  acid    . 

46     „    21 

0  343 

Kopp, 

Wood-spirit 

43     „    23    . 

0-645 

Kopp. 

0-6713 

F.  S. 

Alcohol 

43     „    23 

0-615 

Kopp. 

0  6438 

F.  S. 

Fusel-oil 

44     „    26 

0-564 
0-5873 

Kopp. 

Ethal     .... 

,             , 

0*5059 

F.  S. 

Ether     .... 

• 

0-50342 

t» 

Formic  acid 

45     „   24 

0-536 

Kopp. 

Acetic  acid 

45     „    24 

0-509 

»» 

Butyric  acid 

45     „    21 

0  503 

»» 

Formiate  of  ethyl 

39     „    20 

0-513 

ti 

Acetate  of  methyl 

41     „   21 

0-507 

»» 

Acetate  of  ethyl 

45     „    21 

0-496 

»» 

0-48344 

F.  S. 

Butyratc  of  methyl 

45     „   21 

0-487 

Kopp. 

0-49176 

F.  S. 

Valerate  of  methyl 

45    „    21 

0-491 

Kopp. 

Acetone 

41     „    20 

0-530 

»» 

Benzoic. 

46     „    19 

0-450 

» 

Oil  of  mustard  . 

48     „    28 

0-432 

>» 

Oil  of  turpentine 

0-46727 

F.  S. 

The  specific  heat  of  water  at  different  temperatures  lias 
been  determined  by  Regnault*,  from  whose  experiments  it 
appears  that  the  quantity  of  heat  expressed  in  heat-units^ 
wljich  one  gramme  of  water  loses  in  cooling  down  from  f  to 
0°  C.  is  given  by  the  formula — 

Q  =  <  -f  0-00002  ^2  +  0-0000003  ^ ; 

and  the  specific  heat  C  at  the  temperature  f,  that  is  to  say,  the 
quantity  of  heat  required  to  raise  one  gramme  of  water  from 

f  to  (^  +  1)°,  is  — 
C  =  1  +  0-00004  t  +  0-0000009  <^ 


*  "  Relations,"  &c.  (see  note,  p.  426),  729. 
t  See  page  448. 


SPECIFIC   HEAT. 


429 


From  this  formula,  the  following  numbers  are  obtained: 
Table  VII.  —  Specific  Heat. 


t. 

Q. 

C. 

t. 

150° 

200 

230 

Q. 

C. 

0° 
60 
100 

0000 

50-087 

100-500 

1  -0000 
1-0042 
1-0130 

151-462 
203-200 
234-708 

10262 
1-0440 
0-0568 

Specific  heat  of  gases  and  vapours. — On  this  subject  numerous 
experiments  have  been  made  by  Kegnault  *,  who  finds,  con- 
trary to  the  statement  of  Delaroche  and  Berard,  that  the 
specific  heat  of  a  gas  does  not  vary,  either  with  its  density  or 
with  its  temperature.  The  specific  heat  of  atmospheric  air, 
referred  to  water  as  unity,  is  found  to  be  0*2377  between 
~  30°  and  +  10°  C. ;  it  is  0*2379  between  10*  and  100°; 
and  0-2376  between  100°  and  225°. 

Table  YIII.  contains  Regnault's  determinations  of  the 
specific  heats  of  a  considerable  number  of  gases;  in  column 
A,  as  referred  to  equal  weights  (water  =  1) ;  in  column  B, 
as  referred  to  equal  volumes. 

Table  VIII.  —  Specific  Heat  of  Gases  (Regnatjlt). 


Oxygen   . 
Nitrogen . 
Hydrogen 
Chlorine  . 
Bromine  . 
Nitrous  oxide  . 
Nitric  oxide     . 
Carbonic  oxide 
Carbonic  acid  . 
Sulphide  of  carbon  . 
Sulphurous  acid 
Hydrochloric  acid    . 
Hydrosulphuric  acid 
Ammonia 
Marsh -gas 
Olefiant  gas 
Water-vapour . 
Alcohol -vapour 


A. 

B.   1 

0-2182 

0-2412  ! 

0-2440 

0-2370 

3-4046 

0-2356 

0-1214 

0-2967 

0-0552 

0-2992 

0-2238 

0-3413  ! 

0-2315 

0-2406 

0-2479 

0-2399  ! 

5-2164 

0-3308  i 

0-1575 

0-4146 

0-1553 

0-3489  i 

0-1845 

0  2302  1 

0-2423 

0-2886  1 

0-5080 

02994 

0-5929 

0-3277 

0-3694 

0-3572  , 

0-4750. 

0-2950  ; 

04513 

0-7171  1 

1 

Ether 

Chloride  of  ethyl 
Bromide  of  ethyl 
Sulphide  of  ethyl     . 
Cyanide  of  ethyl 
Chloroform 
Chloride  of  ethylene 
Acetate  of  ethyl 
Acetone  . 
Benzole    . 
Oil  of  turpentine 
Terchloride  of  phos- 
phorus 
Chloride  of  arsenic  . 
Chloride  of  silicon    . 
Bichloride  of  tin 
Bichloride  of  titanium 


A. 

B. 

0-4810 

1-2296 

0-2737 

0-6117 

0-1816 

0-6717 

0-4005 

1-2568 

0-4255 

0-8293 

0-1568 

0-8310 

0-2293 

0-7911 

0-4008 

1-2184 

0-4125 

08341 

0-3754 

10114 

0-5061 

2-3776 

0-1346 

0-6386 

0-1122 

0-7013 

0-1329 

0-7788 

00939 

0-8639 

0-1263 

0  8634 

Compt.  Rend,  xxxvi,  676. 


430  SPECIFIC   nEAT. 


LIQUEFACTION. 

The  melting  point  of  a  body  appears  to  be  influenced  to  a 
minute  but  certain  amount,  by  the  pressure  to  which  it  is 
subjected.  W.  Thomson*,  by  enclosing  transparent  pieces 
of  ice  and  water  in  an  Oersted's  water-compressing  apparatus, 
found  that  the  melting  point  of  the  ice  was  lowered  0-059°  C. 
by  a  pressure  of  8*1  atmospheres,  and  0*129°  by  a  pressure 
of  16*8  atmospheres.  Bunsenf  has  obtained  similar  results 
with  spermaceti  and  paraffin. 


SPERMACETI. 

PARAFFIK. 

Tressure  in 

Solidifving 

ricssurc  in 

JSulidil'ying 

Atmospheres. 

Point. 

Atmosplicrcs. 

Point. 

1      ... 

47-7" 

C. 

1       .  . 

.     46-3°  G 

29     ... 

48-3 

85     .  .  , 

.     48-9 

96     .  .  . 

49-7 

100     .  . 

.     49-9 

141     ... 

50-5 

156     ... 

50-9 

Such  results  are  in  conformity  with  the  deductions  by 
J.  Thomson  J  from  the  mechanical  theory  of  heat. 

The  latent  heat  of  water  was  found  by  Regnault,  and  by 
Provostaye  and  Desains,  to  be  79°  C.  or  142  F.  According 
to  Person,  this  number  denotes  the  quantity  of  heat  required 
to  convert  ice  at  0°  C.  into  water,  but  not  the  total  quantity 
of  the  latent  heat  in  the  water,  inasmuch  as  a  certain  additional 
portion  of  heat  is  rendered  latent  as  the  temperature  of  the  ice 
rises  from  —  2°  to  0°.§  In  six  experiments  on  tjie  fusion  of  ice 
previously  cooled  to  temperatures  between  —2°  and  —21°, 
the  latent  heat  was  found  to  vary  between  79*9  and  80*1,  the 
mean  quantity  being  80°  C,  or  144°  Pah.  Regnault  also 
found  greater  values  for  the  latent  heat  of  water  in  proportion 

*  Phil.  Mag.  [3],  xxxvii.  123.  f  Pogg.  Ann.  Ixxxi.  562. 

t  Edinb.  PhiL  Trans,  vol.  xvi.  §  Ann.  Ch.  Phyg.  [3j,  xxx.  73. 


LATENT    HEAT    OF   VAPOURS. 


431 


as  the  ice  used  in  the  experiments  had  been  cooled  to  a  lower 
temperature.  According  to  Hess,  the  true  latent  heat  of  water 
is  80-34°  C.  =  144*6°  Fah.  For  the  specific  heat  of  ice,  Hess 
finds  the  number  0*533 ;  Person  finds  0*48  for  the  tempe- 
ratures between  —  21°  and  —  2°,  the  specific  heat  of  water 
being  1. 

Table  IX.   contains  the  latent   heats   of  fusion,  and  the 
melting  points  of  various  solids,  as  determined  by  Person.* 

Table  IX.  —  Latent  Heat  of  Fusion. 


Substances. 

Melting  point. 

Latent  Heat. 

Tin     . 

235°  C. 

14-3 

Bismuth 

270 

12-4 

Lead 

332 

5-15 

Alloy  Pb.,  Siij  Big 

96 

5-96 

Alloy  Pb  Sna  Bi 

145 

7-63 

Phosphorus 

44-2 

471 

Sulphur 

115 

9-175 

Nitrate  of  Soda 

310.5 

62-98 

Nitrate  of  Potash 

339 

46-18 

A  mixture  of  1  eq.  Nitrate  of 

Soda  and  1  eq. 

Nitrate  of  Potash     . 

219-8 

51-4 

Phosphate  of  Soda  2NaO,  HC 

),  PO5  +  24HO            36-4 

66-80 

Chloride  of  Calcium  CaCl,  6t 

10          .             .            28-5 

40-70 

Bees-wax  (yellow) 

62-0 

43-51 

Zinc     . 

423-0 

27-46 

LATENT  HEAT  OP  VAPOURS. 

Water,  —  It  is  stated  at  page  5S,  vol.  i.  of  this  work^  that 
the  sum  of  the  latent  and  sensible  heats  of  steam  is  the  same 
at  all  temperatures.  This  is  commonly  known  as  Watt's 
law.  Southern,  on  the  other  hand,  maintained  that  the  latent 
heat  alone  is  constant  at  all  temperatures.  But  the  late 
elaborate  researches  of  Regnault  f  have  shown  that  both  these 


*  Pogg.  Ann.  Ixx.  300  ;  Ann.  Ch.  Phys.  [3],  xxvii.  250. 
■f  "Relations  des Experiences,"  &c.  (see  Note,  p.  426),  271;  also  "Works  of 
Cavendish  Society,"  i.  294. 


432 


LATENT   HEAT   OF   VAPOURS. 


statements  are  incorrect,  and  that  the  total  quantity  of  heat 
(expressed  in  heat-units*),  which  a  unit  of  weight  of  saturated 
aqueous  vapour  contains  at  the  temperature  f  centigrade, 
exceeds  the  amount  contained  in  the  same  weight  of  water  at 
0°,  bj  the  quantity  — 

X  =  606-5  +  0-305  t 

If  from  this,  we  subtract  the  quantity  of  heat  which  a  unit 
of  weight  of  water  at  f  contains,  beyond  tliat  which  is  con- 
tained in  the  same  weight  of  water  at  0°  (see  Regnault's 
determinations  of  the  specific  heat  of  water  at  different  tem- 
peratures, p.  428),  we  sliall  obtain  the  latent  heat  L  of  the 
vapour  of  water  at  the  temperature  f.  The  values  of  X  and 
L  for  various  temperatures  are  given  in  Table  X.,  together 
with  the  tensions  expressed  in  millimetres  and  in  atmospheres. 

Table  X.  —  Latent  Heat  of  Steam. 


Temperature. 

Tension. 

X 

L. 

mm. 

atm. 

0°C 

4-60 

0.006 

60G-5 

606-5 

50 

91-98 

0-121 

621-7 

571-6 

100 

76000 

1-000 

637-0 

536-5 

150 

3581-23 

4-712 

652-2 

500-7 

200 

11688-96 

15-380 

667-5 

464-3 

230 

20926-40 

27-535 

676-6 

441-9 

The  latent  heats  of  the  vapours  of  several  other  liquids  at 
their  boiling  points  have  been  determined  by  Andrews  f,  and 
by  Favre  and  Silbermann.J     The  results  are  given  in — 


*  A  unit  of  heat  is  the  quantity  required  to  raise  the  temperature  of  a  unit 
of  weight  (1  gramme,  1  pound,  &c.)  of  water  at  0°,  by  1°  Centigrade, 
t  Chem.  Soc.  Qu.  J.  i.  27. 
+  Ann.  Ch.  Thys.  [3],  xxxvii.  461. 


TENSION   OF   VAPOURS. 


433 


Table  XI.  —  Latent  Heat  op  Vapours. 


Substances. 

Boiling  point 

Latent  Heat 
of  Vapour. 

Observers. 

Water            .            .            . 

100°     at  760  mm. 

535-9 

Andrews. 

»»                     •                •                • 

100 

536 

F.  andS. 

Iodine 

, 

23-95 

i> 

Bromine 

58     '  „    76*0 

45-60 

A, 

Sulphurous  acid 

, 

94-56 

F.  and  S. 

Terchloride  of  phosphorus     . 

78-5    „    767 

51-42 

A. 

Bichloride  of  tin 

112-5    „    752 

3-053 

>» 

Bisulphide  of  carbon 

46-2    „    769 

86-67 

»> 

Alcohol 

77-9    „    760 

202-40 

„ 

»»              ... 

78-4 

208-92 

F.  S. 

Wood-spirit   . 

65-8    „    767 

263-70 

A. 

i»             •            •            • 

66-5 

263-86 

F.  S. 

Fusel-oil 

132 

121-37 

»> 

Ether 

35-6 

91-11 

»» 

»                 ... 

34-9    „    752 

90-45 

A. 

Amylic  ether 

113 

69-40 

F.  S. 

Acetic  acid     . 

120 

101-91 

^^ 

Formic  acid  . 

100 

120-72 

» 

Valerianic  acid 

175 

103-52 

ji 

Butyric  acid 

16.4 

114  67 

F.  S 

Acetate  of  ethyl 

74 

105.80 

»» 

»>                      •            • 

74-6    „    762 

92-68 

A. 

Acetate  of  methyl 

55        „   762 

110-20 

»> 

Formiate  of  ethyl 

54-3    „   762 

105-30 

'» 

Formiate  of  methyl    . 

32-9    „    752 

117-10 

Iodide  of  ethyl 

71-3    „    760 

46-87 

»> 

Iodide  of  methyl 

42-2     „    752 

4607 

Oxalate  of  ethyl 

184-4    „    779 

72-72 

>» 

Butyrate  of  methyl    . 

93-02  ^^    779 

87-33 

F.  S. 

Ethal 

360-0» 

58-48 

>» 

Oil  of  turpentine 

156 

68-73 

»> 

Terebene 

156 

67-21 

)) 

Oil  of  lemons 

165 

70-02 

n 

Hydrocarbons  — 

(a)C.,H,,    .        . 

198 

59-9 

»» 

(6)C,,H,,    .         . 

255 

59-7 

M 

TENSION   OF   VAPOURS. 

Regnault*  has  made  a  vast  number  of  observations  on  the 
tension  of  aqueous  vapour  in  vacuo,  between  the  temperatures 
of  —32°  and  +  147*5°  C,  and  given  formulaB  of  interpola- 
tion for  calculating  the  tension  at  any  given  temperature 
between  those  limits. 


Ann.  Ch.  Phys.  [3],  xi.  273 


434  TENSION   OF   VAPOURS. 

For  temperatures  between  0°  and  100°  the  interpolation 

formula  is  — 

log  e  =  a  +  hcc*  +  c/3' ; 

in  which  t  denotes  the  temperature,  e  the  tension,  and 
a,  h,  c,  a,  /3  are  constants  whose  values  are  determined  by 
five  equations  of  condition,  obtained  by  substituting  in  the 
preceding  equation  the  cprresponding  observed  values  of  t 
and  e  for  the  temperatures  0°,  25°,  50°,  75°,  and  100°.  (See 
Table,  p.  65,  vol.  i.)     The  values  thus  obtained  are  — 

log  a  =  0-006865036  log  c  =  0-6116485 

log  /3  =  1-9967249  a  =  +  4-7384380. 

log  h  =  2-1340339 

For  temperatures  below  0°,  Regnault  adopts  the  formula — 
e  ■=  a  -\-  ba' ; 
in  which  — 

a;  =  <  -  32  ;  log  5  =  T-4724984  ;  log  u  =  0-0371566 ; 
a  =  +  0-131765. 

For  temperatures  above  100°  C.  the  interpolation  formula 

is  — 

log  e  =  a  —  ha.'  \  X  ^=-  t  —  100° ; 

in  which  — 

log  a  =  1-9977641 ;  log  ^^  =  0*4692291 ; 
a  =  +  5-8267890. 

It  has  not  yet  been  found  possible  to  include  the  whole 
series  of  observations  in  one  formula  of  interpolation. 

From  the  first  and  second  of  these  formulae,  the  follow- 
ing table  of  tensions*  is  calculated  for  every  half  degree 
between  —10°  and  +35°.  This  table  (which  is  the  one 
alluded  to  in  the  note  at  page  94,  vol.  i.)  is  of  great  utility  in 
hygrometric  observations ;  — 

*  Ann.  Ch.  Phys.  [3],  xv.  1 33. 


TENSION   OF   VAPOURS. 

Table  XIL 

Tension  of  Aqueous  Vapour  from  —10°  to  +35°  C 


435 


Degrees. 


-100 
9-5 
90 
8-5 
80 
7-5 
7-0 
6-5 
6-0 
5-5 
5-0 
45 
4-0 
3-5 
3-0 
2-5 
20 
1-5 
1-0 
0-5 
00 

+  0-5 
1-0 
1-5 
2-0 
2-5 
30 
3-5 
40 
4-5 


Tension. 


mm. 
2-078 
2-168 
2-261 
2-356 
2-456 
2-561 
2-666 
2-776 
2-890 
3010 
3-131 
3-257 
3  387 
3-522 
3-662 
3-807 
3-955 
4-109 
4267 
4-430 
4-600 
4-767 
4-940 
5-118 
5-302 
5-491 
5-687 
5-889 
6-097 
6-313 


Diff. 


0-090 
0-093 
0-095 
0-100 
0105 
0-105 
0-110 
0-114 
0-120 
0  121 
0-126 
0130 
0-135 
0-140 
0145 
0-148 
0-154 
0158 
0-163 
0-170 
0-167 
0-173 
0-178 
0-184 
0-189 
0-196 
0-202 
0-208 
0-216 


Degrees. 


+  5-0 

5-5 

6-0 

6-5 

7-0 

7-5 

8-0 

85 

90 

9-5 

10-0 

10-5 

110 

11-5 

12-0 

12-5 

13-0 

13-5 

140 

14-5 

15-0 

155 

16-0 

16-5 

17-0 

17-5 

18-0 

18-5 

19-0 

19-5 


Tension. 


mm. 

6-534 

6-763 

6-998 

7242 

7-492 

7-751 

8-017 

8-291 

8-574 

8-865 

9-165 

9-474 

9-792 

10-120 

10-457 

10-804 

11-162 

11  530 

11-908 

12-298 

12-699 

13-112 

13-536 

13-972 

14-421 

14-882 

15-357 

15-845 

16-346 

16-861 


Diflf. 


0-229 

0-235 

0-244 

0-250 

0-259 

0-265 

0-274 

0-283 

0-291 

0-300 

0-309 

0-318  I 

0  328 

0-337 

0-347 

0-358 

0-368 

0-378 

0-390 

0-401 

0-413 

0-424 

0436 

0-449 

0-461 

0-475 

0-488 

0-501 

0-515 


Degrees. 


+  20-0 
20-5 
21-0 
21-5 
22-0 
22-5 
23-0 
23-5 
24-0 
24-5 
25-0 
25-5 
260 
26-5 
27-0 
27-5 
28-0 
28-5 
29-0 
29-5 
30-0 
30-5 
31-0 
31-5 
32-0 
32-5 
33-0 
33-5 
34-0 
34-5 
35*0 


Tension. 


mm. 
17-391 
17-935 
18-495 
19069 
19-659 
20-265 
20-888 
21-528 
22-184 
22*858 
23550 
24-261 
24-988 
25-738 
26-505 
27-294 
28-101 
28-931 
29-782 
30-654 
31-548 
32-463 
33-405 
34  368 
35-359 
36-370 
37-410 
38-473 
39-565 
40-680 
41-827 


Diff. 


0-544 
0-560 
0-574 
0-690 
0-601 
0-623 
0-640 
0-656 

0  674 
0-692 
0711 
0-727 
0-750 
0-767 
0-789 
0-807 
0-830 
0-851 
0-872 
0-894 
0-915 
0-942 
0963 
0-991 
1-011 
1-030 
1-063 
1092 

1  115 
1-147 


Regnault  has  also  determined  the  tensions  of  several  other 
liquids  in  vacuo.  The  results  (given  in  Table  XIIT.)  were 
obtained  either  by  direct  measurement  of  the  elastic  forces  in 
vacuo,  or  by  determining  the  temperature  of  the  vapour  of  a 
boiling  liquid  under  the  pressure  of  an  artificial  atmosphere. 
The  former  method  was  adopted  for  low,  the  latter  for  high 
temperatures.  The  series  of  experiments  made  by  the  two 
methods  were,  however,  in  all  cases  made  to  include  a  certain 
common   range  of  temperature,  so  that   the   corresponding 


436 


TENSION    OF   VAPOURS. 


curves  of  tension  might  overlap  each  other  within  that  range. 
With  liquids  which  could  be  obtained  perfectly  pure,  such  as 
water  and  sulphide  of  carbon,  the  two  curves  thus  obtained 
were  found  to  coincide  exactly ;  but  with  alcohol,  ether,  and 
still  more  with  chloroform,  which  are  more  difficult  to  purify, 
the  presence  of  foreign  substances  gave  rise  to  more  or  less 
divergence  in  the  results.  Thus  the  tension  of  chloroform 
vapour  at  36°,  was  found  to  be  342*2  mm.  by  the  first 
method,  and  313*4  mm.  by  the  second.  Regnault  finds  that 
an  extremely  small  amount  of  impurity  may  be  detected  in 
this  manner. 


Table  XIIL  —  Tension  op  Vapours. 


Temperature. 

Alcohol. 

Ether. 

Sulphide  of  Carbon. 

Chloroform. 

Oil  of  Turpentine. 

mm. 

mm. 

mm. 

mm. 

mm. 

-21°  C. 

312 

-20 

3*34 

69-2 

-16 

, 

. 

58-8 

-10 

6-50 

113-2 

790 

0 

12-73 

182-3 

127-3 

. 

2-1 

10 

2408 

286-5 

199-3 

130-4 

2-3 

20 

44-00 

434-8 

298-2 

190-2 

4-3 

30 

78-4 

637-0 

434-6 

276-1 

7-0 

40 

134-10 

913-6 

617-5 

364-0 

11-2 

50 

220-3 

1268-0 

8527 

524-3 

17-2 

60 

350-0 

1730  3 

1162-6 

738-0 

26-9 

70 

539-2 

2309-5 

15490 

976-2 

41-9 

80 

812-8 

2947-2 

2030-5 

1367-8 

61-2 

90 

1190-4 

3899-0 

2623-1 

1811-5 

910 

100 

16850 

4920-4 

3321-3 

2354-6 

134-9 

no 

2351-8 

6243-0 

4136-3 

3020  4 

187-3 

116 

. 

7076*2 

120 

3207-8 

5121-6 

3818-0 

257-0 

130 

4351-2 

6260-6 

4721-0 

347-0 

136 

7029-2 

140 

5637-7 

462-3 

150 

7257-8 

604-5 

152 

7617-3 

160 

777*2 

170 

. 

989-0 

180 

. 

12250 

190 

. 

1514-7 

200 

. 

1865-6 

210 

. 

2251-2 

220 

. 

2690-3 

222 

2778-5 

TENSION   OF    VAPOURS.  437 

Vapours  of  saliiie  solutions.  —  It  is  well  known  that  the 
boiling  point  of  a  saline  solution  is  higher  than  that  of  pure 
water,  the  affinity  of  the  water  for  the  salt  being,  in  fact,  an 
additional  obstacle  which  the  heat  must  overcome  before  ebul- 
lition can  take  place.  Nevertheless,  it  appeared  to  Rudberg 
that  the  vapours  rising  from  such  solutions  do  not  exhibit  a 
higher  temperature  than  steam  from  boiling  water ;  a  result' 
which  was  attributed  to  the  sudden  expansion  which  the 
vapour  undergoes  at  the  moment  of  escaping  from  the  liquid. 
Regnault  finds,  however,  that  a  thermometer  having  its  bulb 
immersed  in  the  vapour  of  a  boiling  saline  solution  does  not 
give  a  correct  indication  of  the  temperature  of  that  vapour, 
because  the  bulb  becomes  covered  with  a  film  of  condensed 
water,  and,  therefore,  the  thermometer  exhibits  only  the 
temperature  due  to  the  boiling  of  that  water.  But  when 
proper  precautions  are  taken,  by  the  interposition  of  screens, 
to  prevent,  as  far  as  possible,  this  deposition  of  water,  the 
temperature  of  the  vapour  appears  very  nearly  equal  to  that 
of  the  liquid.  It  is,  however,  extremely  difficult  to  remove 
this  source  of  error  completely. 

The  observation  of  the  elastic  force  of  a  vapour  arising 
from  a  saline  solution  appears  to  afford  excellent  means  of 
detecting  chemical  changes  in  the  constitution  of  the  liquid, 
every  such  change  being  indicated  by  the  occurrence  of  a 
singular  point  in  the  curve  which  represents  the  law  of  the 
tension.  For  example,  in  the  case  of  salts,  like  the  sulphates 
of  sodium,  copper,  iron,  manganese,  &c.,  which  crystallise  at 
different  temperatures  with  different  proportions  of  water, 
Regnault  suggests  that  the  variations  in  the  tension  of  the 
vapour  might  indicate  whether  the  water  is  chemically  com- 
bined with  the  salt  while  still  in  solution,  or  whether  the 
combination  takes  place  at  the  moment  of  crystallisation. 

Mixtures  of  vapours  and  gases,  —  The  law  of  Dalton,  that 
the  tension  of  any  saturated  vapour  in  air  is  the  same  for 

VOL.  II.  I  I 


438 


TENSION   OF    VAPOURS. 


any  given  temperature  as  in  vacuo,  must  be  received  with 
certain  limitations.  It  has  been  ah'eadj  stated  (i.  91)  that 
Regnault  found  the  tension  of  saturated  aqueous  vapour  in 
air  to  be  always  somewhat  less  than  in  vacuo ;  the  differences, 
however,  seldom  exceeding  2  per  cent,  of  the  entire  value. 
The  following  are  a  few  of  the  results  obtained :  — 

Table  XIV. 


Temperature. 

Obierved  Tension  in  Air. 

Calculated  Tension  in  Vacuo. 

^    Difference. 

mm. 

mm. 

0°C. 

4-47 

460 

-0-13 

12-59 

10-31 

10-85 

-0-54 

15 

12-38 

12-70 

-0-32 

21 

18-27 

18-49 

-0-22 

24-69 

22-70 

23-13 

-0-40 

31 

32-97 

33-41 

-0-44 

35-97 

43-39 

44-13 

-0-74 

38 

48-70 

49-30 

-0-60 

Similar  differences  are  observed  with  other  liquids, 
ether  the  following  results  are  obtained :  — 


With 


Table  XV. 


Temperature. 

Tension  of  Ether-vapour. 

In  Air. 

In  Vacuo. 

Difference. 

33-62°  C 

30-97 

26.52 

22-63 

20-05 

19-99 

14-26 

mm. 
705-09 
645-52 
552-67 
479-63 
429-69 
428-88 
337-71 

mm. 
7260 
659-0 
559-2 
484-0 
433-9 
4330 
3410 

mm. 
20-9 
13-4 
6-5 
4-4 
4-2 
4-1 
3  3 

In  air  and  in  hydrogen  gas,  the  tension  of  ether  vapour  was 
found  to  be  always  lower  than  in  vacuo,  unless  the  gas  was 
strongly  compressed;  in  carbonic  acid  gas,  which  (as  a  liquid) 


TENSION   OF   VAPOURS. 


439 


dissolves  ether  in  considerable  quantity,  the  tension  never 
becomes  equal  to  that  in  vacuo. 

The  tension  of  a  vapour  in  a  gas  is  very  much  affected  by 
the  condensation  of  the  vapour  on  the  sides  of  the  vessel,  an 
effect  which  takes  place  considerably  below  the  point  of 
saturation.  Regnault  is  of  opinion  that  Dalton'3  law  with 
regard  to  the  tensions  of  vapours  in  gases  could  never  be 
strictly  true,  unless  the  gas  were  enclosed  in  a  vessel  whose 
walls  were,  to  a  certain  thickness,  formed  of  the  liquid  itself. 

Vapours  of  mixed  liquids.  —  Gay-Lussac  found  that  the 
tension  of  the  vapour  arising  from  two  or  more  mixed  liquids 
is  equal  to  the  sum  of  the  tensions  of  the  vapours  which  each 
would  produce  separately.  The  more  recent  experiments  of 
Magnus  and  of  Kegnault  have  shown  that  this  law  is  true,  or 
nearly  true,  only  when  the  liquids  are  quite  immiscible,  such 
as  benzol  and  water.  When  the  liquids  are  mutually 
soluble,  but  not  in  all  proportions,  the  tension  of  the  mixed 
vapour  is  much  less  than  the  sum  of  the  separate  tensions. 
With  ether  and  water  it  scarcely  differs  from  the  tension 
of  the  ether- vapour  alone ;  thus :  — 

Table  XVI. 


Temperature. 

Tension  of 
water- vapour. 

Tension  of 
ether-vapour. 

Sura  of 
tensions. 

Observed  tens'.on  of 
mixed  vapour. 

15-66°  C. 

24-21 

33-08 

mm. 
1316 
2-2-47 
37-58 

mm.' 
361-8 
510-0 
711-1 

mm. 
374*96 
532-47 

748-68 

mm. 
362-95 
51008 
71002 

When  the  mixed  liquids  dissolve  in  one  another  in  all  pro- 
portions, the  tension  of  the  mixed  vapour  is  in  most  cases 
greater  than  that  of  the  less  volatile,  but  less  than  that  of  the 
more  volatile  substance ;  such,  for  example,  is  the  case  with 
mixtures  of  ether  and  sulphide  of  carbon.  In  a  mixture  of 
benzol  and  alcohol,  however,  the  tension  of  the  mixed  vapour 

II  2 


440 


CONDUCTION   OF    HEAT. 


is  greater  than  that  of  either  of  the  separate  vapours.     With 
this  mixture  Regnault  obtained  the  results  given  in  — 


Table  XVIL 


Temperature. 

Tension  of  vapour,                                          J 

Of  the  mixture. 

OfalcohoL 

Of  benzol. 

7-22°  C. 

4317 

40-4 

201 

9-98 

50-22 

46-8 

24-2 

13-11 

59-66 

54-4 

29-2 

16-05 

69-43 

62-7 

350 

18-59 

79-35 

71-0 

41-0 

When  the  liquids  do  not  mix,  but  dispose  themselves  in 
layers,  the  more  volatile  liquid  forming  the  lower  stratum, 
and  the  ebullition  being  but  feeble,  the  temperature  and 
corresponding  vapour-tension  agree  with  Gay-Lussac's  law. 
But  with  a  brisk  fire  and  violent  ebullition,  the  temperature 
remains  nearly  at  the  limit  at  which  the  more  volatile  liquid 
would  boil  by  itself  under  the  same  pressure. 


CONDUCTION   OF   HEAT. 

In  metals,  —  From  the  experiments  of  Wiedemann  and 
Franz*,  it  appears  that  the  metals  follow  each  other  with 
regard  to  their  heat-conducting  power,  in  the  same  order  as 
with  regard  to  their  power  of  conducting  electricity ;  and, 
moreover,  that  the  numbers  which  express  their  relative 
heat-conducting  powers,  do  not  differ  from  those  which 
express  their  relative  powers  of  conducting  electricity,  more 
than  the  latter  numbers,  as  determined  by  different  observers, 
differ  from  each  other. 

The  heat-conducting  power  of  metals  appears  also  to  di- 
minish as  their  temperature  rises. 

*  Phil.  Mag.  [4],  vii.  33. 


CONDUCTION   OF   HEAT. 
Table  XVni. 


441 


Electric-conducting  power  according  to 

Heat- 

conducting 

power. 

Metals. 

Riess. 

Becquerel. 

Lenz. 

Silver 

100 

100 

100 

100 

Copper 

66-7 

91-5 

73-3 

73-6 

Gold 

59-0 

64-9 

58-5 

53-2 

Brass 

18-4 

21-5 

23-6 

Tin   . 

10  0 

140 

22-6 

14-5 

Iron  . 

120 

12-35 

13-0 

11-9 

Steel 

11-6 

Lead 

7-0 

8-27 

10-7 

8-5 

Platinum 

10-5 

7-93 

10-3 

8-4 

German  silver    . 

5-9 

6-3 

Bismuth     . 

1-9 

1-8 

Conduction  of  heat  in  crystallised  bodies.  —  Bodies  of  perfectly 
homogeneous  structure  conduct  heat  with  equal  facility  in  all 
directions ;  so  likewise  do  crystallised  bodies  belonging  to  the 
regular  system ;  but  in  crystals  belonging  to  any  other  system, 
the  rate  of  conduction  is  different  in  different  directions.  This 
subject  has  been  very  ingeniously  investigated  by  Senar- 
rnont*,  whose  method  of  observation  was  as  follows: — A 
small  tube  of  platinum  was  inserted  through  the  centre  of 
a  flat  cylindrical  plate  of  the  crystal  in  the  direction  of  the 
axis  J  the  tube  being  bent  at  right  angles  at  the  lower  ex- 
tremity and  heated  by  a  lamp,  and  a  current  of  air  made  to 
pass  through  the  tube  by  means  of  an  aspirator.  The  two 
bases  of  the  cylindrical  plate  were  covered  with  wax,  which, 
being  melted  by  the  heat,  traced  on  the  surface  a  curve  line, 
whose  form  was  determined  by  the  conducting  power  of  the 
crystal  in  diflPerent  directions.  Plates  of  non-crystalline  sub- 
stances, such  as  glass  and  zinc,  treated  in  this  manner,  gave 
circles  having  their  centres  in  the  axis  of  the  platinum-tube. 
On  a  plate  of  calc-spar,  cut  perpendicularly  to  the  axis  of 
symmetry  (the  optic  axis),  the  curves  are  circles  with  their 
centres  in  the  axis.     On  plates  parallel  to  the  direction  of 

*  Ann.  Ch.  Phys.  [3],  xxi.  45. 
I  I  3 


442  CONDUCTION   OF   HEAT. 

natural  cleavage,  the  curves  are  also  circles,  having  a  slight 
tendency  to  elongate  in  the  direction  of  the  principal  section. 
On  plates  cut  parallel  to  the  axis  of  symmetry,  and  at  right 
angles  to  one  of  the  faces  of  the  primary  rhombohedron,  tlie 
curves  are  ellipses,  having  their  transverse  diameter  in  the 
direction  of  the  axis  of  symmetry.  The  ratio  of  the  axes  of 
the  ellipse  thus  formed  is  I'llS  :  1.  Similar  results  are 
obtained  with  quartz,  the  ratio  of  the  axes  being  1*31  :  1; 
also  with  crystals  belonging  to  the  square  prismatic  system, 
such  as  rutile,  idocrase,  and  subchloride  of  mercury.  In 
crystals  belonging  to  the  right  prismatic,  oblique  prismatic, 
and  doubly  oblique  prismatic  systems,  —  that  is  to  say,  in 
crj'stals  having  two  axes  of  double  refraction,  —  three  direc- 
tions are  found  at  right  angles  to  each  other,  in  which  the 
thermal  curves,  obtained  in  the  manner  above  described,  are 
ellipses.     Hence  it  is  inferred  that :  — 

1.  In  crystalline  media  having  two  optic  axes,  supposing 
the  medium  to  be  indefinitely  extended  in  all  directions,  and  a 
centre  of  heat  to  exist  within  it,  the  isothermal  surfaces  are 
ellipsoids  with  three  unequal  axes. 

2.  In  crystals  with  one  optic  axis,  the  isothermal  surfaces 
are  ellipsoids  of  revolution  round  that  axis. 

3.  In  crystals  belonging  to  the  regular  system,  and  in 
homogeneous  uncrystallised  media,  the  isothermal  surfaces 
are  spherical. 

Uncrystallised  bodies,  however,  acquire  axes  of  different 
heat-conducting  power  when  their  molecular  structure  is 
altered  by  pressure,  traction,  or  hardening.  Plates  of  glass 
subjected  to  lateral  pressure,  and  heated  in  the  manner  above 
described,  exhibit  distinct  thermic  ellipses,  having  their 
shorter  axes  in  the  direction  of  the  pressure,  that  is,  of  the 
greatest  density  (Senarmont).  It  is  well  known  that  glass, 
and  other  transparent  non-crystalline  bodies,  when  similarly 
treated,  acquire  the  power  of  double  refraction. 

Crystalline  media  likewise  exhibit  peculiar  characters  in 


CONDUCTION   OF   HEAT.  443 

the  transmission  of  heat  by  radiation  as  well  as  by  conduction. 
Through  crystals  with  one  optic  axis,  heat  is  radiated  in 
diflferent  quantity  and  also  of  different  quality  (i.  37),  accord- 
ing as  it  passes  in  a  direction  parallel  or  perpendicular  to  that 
axis.  In  crystals  with  two  optic  axes,  the  quantity  and  quality 
of  the  transmitted  heat  differ  according  as  the  direction  of 
transmission  coincides  with  one  or  other  of  the  three  axes  of 
elasticity  (Knoblauch).* 

Conducting  power  of  wood. — The  dependence  of  heat-con- 
duction upon  molecular  arrangement  is  exhibited  by  organic 
structures  as  distinctly  as  by  crystalline  media.  This  subject 
has  been  very  ingeniously  investigated  by  Dr.  Tyndall  f,  who 
has  examined  the  conducting  power  of  various  organic  sub- 
stances, especially  of  wood.  The  bodies  cut  into  cubes  of 
equal  size,  were  enclosed  between  two  chambers  filled  with 
mercury,  that  liquid  being  confined  on  the  sides  next  the 
cube  by  membranous  diaphragms,  with  which  the  cube  was  in 
close  contact.  The  mercury  in  one  of  the  chambers  was  heated 
by  a  spiral  of  platinum  wire  immersed  in  it,  and  connected 
with  a  galvanic  battery.  The  heat  thus  generated  was  trans- 
mitted through  the  organic  substance  to  the  mercury  in  the 
other  chamber,  and  the  quantity  of  heat  thus  communicated 
in  a  given  time,  was  measured  by  means  of  a  thermo-electric 
couple  connected  with  a  galvanometer.  By  transmitting  heat 
in  this  manner  through  cubes  of  wood  in  different  directions, 
it  was  found  that ; 

At  all  points  not  situated  in  the  centre  of  the  tree,  wood 
possesses  three  unequal  axes  of  calorific  conduction.  The 
first  and  principal  axis  is  parallel  to  the  fibres  of  the  wood ; 
the  second  and  intermediate  axis  is  perpendicular  to  the 
fibres  and  to  the  ligneous  layers ;  and  the  third,  and  least 
axis,  is  perpendicular  to  the  fibre  and  parallel  to  the  layers. 

These  axes  of  heat-conduction  coincide  with  the  axes  of 

*  Pogg.  Ann.  Ixxxv.  169  ;  xciv   161.  f  rhil.  Mag.  [4],  vi.  121. 

II  4 


444  MECHANICAL   EQUIVAJ.ENT   OF   HEAT. 

elasticity,  which  Savart  discovered  by  observing  the  figures 
of  sand  formed  on  plates  of  wood  when  thrown  into  acoustic 
vibration.  The  same  directions  are  likewise  axes  of  cohesion 
and  of  permeability  to  liquids,  AYood  of  any  kind  may  be 
most  easily  split  by  laying  the  blade  of  the  cutting  instru- 
ment parallel  to  the  fibres  and  across  the  annual  rings  ;  the 
direction  of  least  cohesion  is,  therefore,  perpendicular  to  the 
fibres,  and  parallel  or  tangential  to  the  rings.  The  direction 
of  greatest  resistance  is  parallel  to  the  fibres.  With  regard 
to  permeability,  it  is  well  known  that  plates  of  wood  cut 
perpendicularly  to  the  fibres  are  not  fit  for  the  bottoms  of 
casks  to  hold  liquids ;  also,  that  in  cutting  staves  for  casks, 
it  is  indispensable  to  cdt  them  across  the  woody  layers, 
the  direction  parallel  to  the  layers  being  that  of  least  per- 
meability. 

It  may,  therefore,  be  stated  as  a  general  law,  that :  the 
axes  of  calorific  conduction  in  wood  coincide  with  the  axes  of 
elasticity,  cohesion  and  permeability  to  liquids,  the  greatest  with 
the  greatest,  and  the  least  icith  the  least 

The  heat-conducting  power  of  wood  does  not  bear  any 
definite  relation  to  its  density.  American  birch,  which  is 
one  of  the  lightest  woods,  conducts  heat  better  than  any 
other.  Oak  and  Coromandel  wood,  which  are  very  dense, 
conduct  nearly  as  well ;  but  iron-wood,  which  has  the  enor- 
mous density  of  1*426,  is  very  low  in  the  scale  of  conduction. 

RELATION  BETWEEN  HEAT  AND  MECHANICAL  FORCE  OR 
WORK. — DYNAMICAL  THEORY  OF  HEAT. 

Heat  and  motion  are  convertible  one  into  the  other.  The 
powerful  mechanical  effects  produced  by  the  elasticity  of  the 
vapours  evolved  from  heated  liquids  afford  abundant  illus- 
tration of  the  conversion  of  heat  into  motion  ;  and  the 
production  of  heat  by  friction  shows  with  equal  clearness 
that  motion  may  be  converted  into  heat.     That  the  rise  of 


MECHANICAL  EQUIVALENT  OF  HEAT.       445 

temperature  thus  produced  is  not  due  to  any  change  in  the 
heat-capacity  of  the  bodies,  is  strikingly  shown  in  Davy's 
experiment  of  melting  ice  by  rubbing  two  plates  of  the 
substance  together  in  vacuo  (i.  101);  and  Count  Rumford's 
observations  on  the  heat  produced  by  the  boring  of  ordnance 
point  to  the  same  conclusion.  In  these  and  all  similar  cases, 
the  heat  appears  as  a  direct  result  of  the  force  expended: 
the  motion  is  converted  into  heat. 

But  the  connection   between  heat  and  mechanical  force 
appears  still  more  intimate  when  it  is  shown  that  they  are 
related  by  an  exact  numerical  law,  a  given  quantity  of  the 
one    being  always  convertible    into   a  determinate  quantity 
of    the    other.      The    first    approximate    determination     of 
this  numerical  relation — the  mechanical  equivalent  of  heat — 
was  made  by  Count  Rumford  in  the  following  manner:  A 
brass  cylinder,  enclosed  in  a  box  containing  a  known  weight  of 
water  at  60°  F.,  was  bored  by  a  steel  borer  made  to  revolve 
by  horse-power,  and  the  time  noted  which  elapsed  before  the 
water  was  raised  to  the  boiling-point  by  the  heat  resulting 
from  the  friction.      In  this  manner  it  was  found  that  the 
heat  required  to  raise  the  temperature  of  a  pound  of  water, 
1°  F.,  is  equivalent  to  1034   times   the  force  expended    in 
raising  a  pound  weight  one  foot  high,  or  to  1034  foot-pounds, 
as  it  is  technically  expressed.     This  estimate  is  now  known 
to  be  too  high,  no   account  having  been  taken  of  the  heat 
communicated  to  the  containing  vessels,  or  of  that  which  was 
lost  by  dispersion  during  the  progress  of  the  experiment. 

For  the  most  exact  determinations  of  the  mechanical  equi- 
valent of  heat,  we  are  indebted  to  the  careful  and  elaborate 
experiments  of  Mr.  J.  P.  Joule.  From  experiments  made 
in  the  years  1840-1843,  on  the  relations  between  the  heat 
and  mechanical  power  generated  by  the  electric  current, 
Mr.  Joule  was  led  to  conclude  that  the  heat  required  to 
raise  the  temperature  of  a  pound  of  water  1°  F.,  is  equiva- 
lent to   838    foot-pounds ;    and  a  nearly   equal   result   was 


446 


MECHANICAL    EQUIVALENT   OF   HEAT. 


afterwards  obtained  by  experiments  on  the  condensation  and 
rarefaction  of  gases ;  but  this  estimate  has  since  been  found 
to  be  likewise  too  high. 

The  most  trustworthy  results  are,  however,  obtained  by 
measuring  the  quantity  of  heat  generated  by  the  friction 
between  solids  and  liquids.  It  was  for  a  long  time  believed 
that  no  heat  was  evolved  by  the  friction  of  liquids  and  gases. 
But,  in  1842,  Meyer  showed  that  the  temperature  of  water 
may  be  raised  22°  or  23°  F.  by  agitating  it.  The  warmth 
of  the  sea  after  a  few  days  of  stormy  weather  is  also,  pro- 
bably, an  effect  of  fluid  friction. 

In  1843  Mr.  Joule  showed  that  heat  is  evolved  in  the 
passage  of  water  through  narrow  tubes,  and  that  each  degree 
of  heat  per  pound  of  water  required  for  its  evolution  in  this 
way  a  force  of  770  foot-pounds.  In  subsequent  experiments, 
a  paddle-wheel  was  employed  to  produce  fluid  friction,  and 
the  equivalents  781*5,  782*1  and  787*6  obtained  from  the 
agitation  of  water,  sperm-oil,  and  mercury  respectively. 

The  apparatus  finally  employed  by  Mr.  Joule*  in  the 
determination  of  this  important  constant,  by  means  of  the 
■p.  21  friction  of  water,  consisted  of  a  brass  paddle- 
wheel  furnished  with  eight  sets  of  revolving 
vanes,  working  between  four  sets  of  stationary 
vanes.  This  revolving  apparatus,  of  which  fig. 
21  shows  a  vertical  and  fig.  22  a  Fig.  2L 
horizontal  section,  was  firmly  fitted 
into  a  copper  vessel  (A,  fig.  23) 
containing  water,  in  the  lid  of  which 
were  two  necks,  one  for  the  axis  to 
revolve  in  without  touching,  the  other  for  the  insertion  of 
a  thermometer.  A  similar  apparatus,  but  made  of  iron, 
and  of  smaller  size,  and  having  six  rotatory  and  eight  sets  of 
stationary  vanes,  was  used  for  experiments  on  the  friction 
of  mercury.  The  apparatus  for  the  friction  of  solids  con- 
*  Phil.  Trans.  1850,  i.  61  ;  Chem.  Soc.  Qu.  J.  iii.  316. 


MECHANICAL   EQUIVALENT   OF   HEAT. 


447 


sisted  of  a  vertical  axis  carrying  a  bevelled  cast-iron  wheel, 
against  which  a  fixed  bevelled  wheel  was  pressed  by  a  lever. 
The  wheels  were  enclosed  in  a  cast-iron  vessel  filled  with 
mercury,  the  axis  passing  through  the  lid.    In  each  apparatus 


Fig.  23. 


motion  was  given  to  the  axis  by  the  descent  of  leaden  weights 
suspended  by  strings  from  the  axes  of  two  wooden  pulleys  w, 
one  of  which  is  shown  at  p  (fig.  23),  their  axes  being  supported 
on  friction-wheels  dd;  and  the  pulleys  were  connected  by  fine 
twine  with  a  wooden  roller  r,  which,  by  means  of  a  pin,  could 
be  easily  attached  to  or  removed  from  the  friction  apparatus. 

The  mode  of  experimenting  was  as  follows  :  The  tempera- 
ture of  the  frictional  apparatus  having  been  ascertained,  and  the 
weights  wound  up,  the  roller  was  fixed  to  the  axis,  and  the  pre- 
cise height  of  the  weights  ascertained,  after  which  the  roller  was 
set  at  liberty,  and  allowed  to  revolve  till  the  weights  touched 
the  floor.  The  roller  was  then  detached,  the  weights  wound 
up  again,  and  the  friction  renew^ed.  This  having  been 
repeated  twenty  times,  the  experiment  was  concluded  with 
another  observation  of  the  temperature  of  the  apparatus. 
The  mean  temperature  of  the  apartment  was  ascertained  by 
observations  made  at  the  beginning,  middle,  and  end  of  each 
experiment.  Corrections  were  made  for  the  effects  of  radia- 
tion and  conduction  ;  and,  in  the  experiments  with  water,  for 
the  quantities  of  heat  absorbed  by  the  copper  vessel  and  the 


448       MECHANICAL  EQUIVALENT  OF  HEAT. 

paddle-wheel.  In  the  experiments  with  mercury  and  cast- 
iron,  the  heat-capacity  of  the  entire  apparatus  was  ascer- 
tained by  observing  the  heating  effect  which  it  produced  on 
a  known  quantity  of  water  in  which  it  was  immersed.  In  all 
the  experiments,  corrections  were  also  made  for  the  velocity 
with  which  the  weights  came  to  the  ground,  and  for  the 
friction  and  rigidity  of  the  strings.  The  thermometers  used 
were  capable  of  indicating  a  variation  of  temperature  as  small 
as  -j^-Q  of  a  degree  Fahrenheit 

The  following  table  contains  a  summary  of  the  results 
obtained  by  this  method  ;  the  second  column  gives  the 
results  as  they  were  obtained  in  air ;  the  third  column,  the 
same  results  corrected  for  a  vacuum. 

Material  Equivalent  Equivalent 

employed.  in  air.  in  vacuo.  Mean. 

Water    .     .     .     773-640  772-692  772-692 

r  773-762  772-814]  ^^.  ^.„ 

Mercury     .     .[^^^_^^^  ^^^.^^J  774-083 

Cast-iron     .     .  ( "''"^^^  l''-'"']  1U-9S1 

1774-880  773-930  J 

In  the  experiments  with  cast-iron,  the  friction  of  the  wheels 
produced  a  considerable  vibration  of  the  frame-work  of  the 
apparatus  and  a  loud  sound  ;  it  was  therefore  necessary  to 
make  allowance  for  the  quantity  of  force  expended  in  pro- 
ducing these  effects.  The  number  772*692,  obtained  by  the 
friction  of  water,  is  regarded  as  the  most  trustworthy ;  but 
even  this  may  be  a  little  too  high ;  because,  even  in  the  friction 
of  fluids,  it  is  imjoossible  entirely  to  avoid  vibration  and  sound. 

The  conclusions  deduced  from  these  experiments  are  — 

1.  TJiat  the  quantity  of  heat  proditced  hy  the  friction  of  bodies, 
ivhether  solid  or  liquid,  is  alicays  proportional  to  the  force 
expended, 

2,  That  the  quantity  of  heat  capable  of  increasing  the  tempera- 
ture of  \  lb.  of  loater  {weighed  in  vacuo,  and  betioeen  55°  and  60°) 
by  1°  F.,  requires  for  its  evolution  the  expenditure  of  a  mechanical 


DYNAMICAL  THEORY  OF  HEAT.        449 

force  represented  by  the  fall  of  772  lbs.  through  the  space  of  1 
foot 

Or,  the  heat  capable  of  increasing  the  temperature  of  1  gramme 
of  water  by  1°  cent,,  is  equivalent  to  a  force  represented  by  the  fall 
of  423*55  grammes  through  the  space  of  1  metre.  This  is  con- 
sequ£ntly  the  effect  of  a  "  unit  of  heat^"* 

Kupffer*  has  also  determined  the  mechanical  equivalent  of 
heat  by  comparing  the  expansion  which  a  metal  wire  suffers 
by  heat  with  the  elongation  produced  by  stretching  it  with 
a  given  weight.  By  this  method,  which  does  not  appear  to  be 
quite  so  accurate  as  that  above  described,  it  is  found  that  the 
heat  necessary  to  raise  a  pound  of  water  1°  Fahrenheit,  is 
equivalent  to  661  foot-pounds. 


DYNAMICAL  THEORY  OF  HEAT. 

The  constant  relation  between  heat  and  work  affords  a 
powerful  argument  in  favour  of  the  mechanical  or  dynamical 
theory  of  heat — the  theory  which  rests  on  the  hypothesis 
that  HEAT  IS  MOTION.  This  theory  has  received,  of  late 
years,  many  important  additions  and  developments,  chiefly 
by  the  labours  of  Clausius,  Joule,  Rankine,  and  W.  Thompson. 
It  is  impossible,  within  the  limits  of  this  Supplement,  to  give 
even  a  brief  account  of  the  whole  of  these  valuable  researches ; 
but  the  leading  points  of  the  theory  may,  perhaps,  be  suffi- 
ciently elucidated  by  the  following  summary  of  two  remark- 
able papers  lately  published  in  "  Poggendorff 's  Annalen,"  one 
by  Kronig,  entitled  "Fundamental  Principles  of  a  Theory 
of  Gases ;  "f  the  other,  by  Clausius,  '^  On  the  Kind  of  Motion 
which  we  call  Heat."  % 

*  Phil.  Mag.  [4],  xli.  393. 

f  Grundzuge  einer  Theorie  der  Gase  ;  von  A.  Kronig.  Pogg.  Ann.  xcix. 
315. 

X  Ueber  die  Art  der  Bewegung  welche  wir  Warme  nennen  ;  von  R. 
Clausius.  Pogg.  Ann.  c.  353.  See  also  a  former  paper  by  Clausius,  "  Ueber 
die  bewegende  Kraft  der  Warme,"  ibid.  Ixxix.  394. 


450         DYNAMICAL  THEORY  OF  HEAT. 

First,  then,  it  is  assumed  that  the  particles  of  all  bodies 
are  in  constant  motion,  and  that  this  motion  constitutes  heat, 
the  kind  and  quantity  of  motion  varying  according  to  the 
state  of  the  body,  whether  solid,  liquid,  or  gaseous. 

In  gases,  the  molecules — each  molecule  being  an  aggregate 
of  atoms — are  supposed  to  be  constantly  moving  forward  in 
straight  lines,  and  with  a  constant  velocity,  till  they  impinge 
against  each  other  or  against  an  impenetrable  wall.  This 
constant  impact  of  the  molecules  produces  the  expansive 
tendency  or  elasticity,  which  is  the  peculiar  characteristic  of 
the  gaseous  state.  The  rectilinear  movement  is  not,  however, 
the  only  one  with  which  the  particles  are  affected.  For  the 
impact  of  two  molecules,  unless  it  takes  place  exactly  in  the 
line  joining  their  centres  of  gravity,  must  give  rise  to  a 
rotatory  motion ;  and,  moreover,  the  ultimate  atoms  of  which 
the  molecules  are  composed  may  be  supposed  to  vibrate 
within  certain  limits,  being,  in  fact,  thrown  into  vibration  by 
the  impact  of  the  molecules.  This  vibratory  motion  is  called, 
by  Clausius,  the  motion  of  the  constituent  atoms  (^Deicegimgen 
der  Bestandtheile).  The  total  quantity  of  heat  in  the  gas  is 
made  up  of  the  progressive  motion  of  the  molecules,  together 
with  the  vibratory  and  other  motions  of  the  constituent 
atoms ;  but  the  progressive  motion  alone,  which  is  the  cause 
of  the  expansive  tendency,  determines  the  temperature.  Now, 
the  outward  pressure  exerted  by  the  gas  against  the  con- 
taining envelope,  arises,  according  to  our  hypothesis,  from  the 
impact  of  a  great  number  of  gaseous  molecules  against  the 
sides  of  the  vessel.  But,  at  any  given  temperature,  that  is, 
with  any  given  velocity,  the  number  of  such  impacts  taking 
place  in  a  given  time,  must  vary  inversely  as  the  volume  of 
the  given  quantity  of  gas  ;  hence  the  pressure  varies  inversely 
as  the  volume  or  directly  as  the  density,  which  is  Mariotte's  law. 

When  the  volume  of  the  gas  is  constant,  the  pressure 
resulting  from  the  impact  of  the  molecules  is  proportional 
to  the  sum  of  the  masses  of  all  the  molecules  multiplied  into 


DYNAMICAL   THEORY   OF   HEAT.  451 

the  squares  of  their  velocities ;  in  other  words,  to  the  so- 
called  vis  viva  or  living  force  of  the  progressive  motion.  If, 
for  example,  the  velocity  be  doubled,  each  molecule  will 
strike  the  sides  of  the  vessel  with  a  two-fold  force,  and  its 
number  of  impacts  in  a  given  time  will  also  be  doubled  ; 
hence  the  total  pressure  will  be  quadrupled. 

Now  we  know  that  when  a  given  quantity  of  any  perfect 
gas  is  maintained  at  a  constant  volume,  it  tends  to  expand 
by  -j^  of  its  bulk  for  each  degree  centigrade.  Hence  the 
pressure  or  elastic  force  increases  proportionately  to  the  tem- 
perature reckoned  from  —  273°  C.  ;  that  is  to  say,  to  the 
absolute  temperature.  Consequently,  the  absolute  temperature 
is  proportional  to  the  vis  viva  of  the  progressive  motion,* 

Moreover,  as  the  motions  of  the  constituent  particles  of  a 
gas  depend  on  the  manner  in  which  its  atoms  are  united,  it 
follows  that  in  any  given  gas  the  different  motions  must  be 
to  one  another  in  a  constant  ratio  ;  and  therefore  the  vis  viva 
of  the  progressive  motion  must  be  an  aliquot  part  of  the 
entire  vis  viva  of  the  gas ;  hence,  also,  the  absolute  tempera- 
ture is  proportional  to  the  total  vis  viva  arising  from  all  the 
motions  of  the  particles  of  the  gas. 

From  this  it  follows  that  the  quantity  of  heat  which  must 
be  added  to  a  gas  of  constant  volume  in  order  to  raise  its 

*  Suppose  a  vessel  of  the  form  of  a  rectangular  parallelopiped,  the  length  of 
whose  sides  are  x,  y,  z,  to  contain  n  gas-molecules,  each  having  the  mass  m. 

Suppose,  also,  the  space  enclosed  by  this  vessel  to  be  divided  into  —  equal 

cubes  ;  and  at  a  given  instant  let  there  be  in  each  of  these  cubes  six  gas- 
molecules,  moving  severally  in  the  directions  -f  x,  — x,  +y,  — y,  +  z,  — z,  and 
with  the  common  velocity  c.  Let  it  also  be  supposed  that  the  molecules  exert 
no  mutual  action  upon  each  other,  but  pass  without  hindrance  from  side  to 
side  of  the  vessel.  It  is  required  to  determine  the  pressure  which  the  gas 
exerts  against  one  of  the  sides,  i/z,  of  the  vessel.  The  pressure  arising  from 
the  impact  of  a  single  gas-molecule  is  mca,  if  a  denote  the  number  of 
impacts  which  take  place  in  a  unit  of  time.  Now,  a  molecule  moving  at  right 
angles  to  yz,  or  parallel  to  x,  strikes  against  yz  every  time  that  it  passes  over 
the  space  2x  ;  therefore  «=— 

To  find  the  total  pressure  P  upon  i/z,  the  quantity,  mca,  must  be  multiplied 


452  DYNAMICAL  THEORY  OF  HEAT. 

temperature  by  a  given  amount,  is  constant  and  independent 
of  the  temperature.  In  other  words,  the  specific  heat  of  a 
gas  referred  to  a  given  volume,  is  constant,  a  result  wliicli 
agrees  with  the  experiments  of  Regnault,  mentioned  at  page 
429.  This  result  may  be  otherwise  expressed  as  follows; 
The  total  vis  viva  of  the  gas  is  to  the  vis  viva  of  the  progressive 
motion  of  the  molecules,  ichich  is  the  measure  of  the  temperature^ 
in  a  constant  ratio.  This  ratio  is  different  for  different  gases, 
and  is  greater  as  the  gas  is  more  complex  in  its  constitution ; 
in  other  words,  as  its  molecules  are  made  up  of  a  greater 
number  of  atoms.  The  specific  heat  referred  to  a  constant 
pressure  is  known  to  differ  from  the  true  specific  heat  only 
by  a  constant  quantity. 

The  relations  just  considered  between  the  pressure,  volume 
and  temperature  of  gases,  presuppose,  however,  certain  con- 
ditions of  molecular  constitution,  which  are,  perhaps,  never 
rigidly  fulfilled  ;  and  accordingly,  the  experiments  of  Magnus 
and  Regnault  show  (i.  13)  that  gases  do  exhibit  slight 
deviations  from  Gay-Lussac  and  Mariotte's  laws.  What 
the  conditions  are  which  strict  adherence  to  these  laws  would 

by  the  number  of  molecules  which  move  parallel  to  x,  which  number,  since 

two  atoms  out  of  every  six  arc  parallel  to  x,  is  — .     Hence  P  =  m.c , —  *  - 
^  ^  '3  •2x    3- 

And  the  pressure  p  upon  a  unit  of  surface  of  the  side  yz/\B  p=  m.c .  —  -  ~  —  ; 

2x     3  1/z 

or  if  we  put  xyz  =  v,  and  leave  out  the  constant  factor  : 

nmc* 

This  expression  shows  that  the  pressure  exerted  upon  a  unit  of  surfiice  is 
tlie  same  for  each  side  of  the  vessel  ;  also,  that  the  pressure  is  inversely 
in  proportion  to  the  volume  of  the  gas,  which  is  Mariotte's  law. 

The  product,  mc";  or  the  vis  viva  of  an  atom,  is  tlie  expression  of  the  tem- 
perature reckoned  from  the  absolute  zero,  or  — 273°  C. 

If,  in  the  preceding  value  of  p,  we  put  vie-  =  t,  we  have 

nt, 

p=i; 

that  is  to  say,  when  the  volume  is  constant,  the  pressure  varies  directly  as  the 
absolute  temperature  (Kronig). 


DYNAMICAL  THEORY  OF  HEAT.         453 

require,  will  be  better  understood  by  considering  the  differ- 
ences of  molecular  constitution  which  must  exist  in  the  solid, 
liquid,  and  gaseous  states. 

A  movement  of  molecules  must  be  supposed  to  exist  in  all 
three  states.  In  the  solid  state,  the  motion  is  such  that  the 
molecules  oscillate  about  certain  positions  of  equilibrium, 
which  they  do  not  quit,  unless  they  are  acted  upon  by 
external  forces.  This  vibratory  motion  may,  however,  be 
of  a  very  complicated  character.  The  constituent  atoms  of 
a  molecule  may  vibrate  separately ;  the  entire  molecules  may 
also  vibrate  as  such  about  their  centres  of  gravity,  and  the 
vibrations  may  be  either  rectilinear  or  rotatory.  Moreover, 
when  extraneous  forces  act  upon  the  body,  as  in  shocks,  the 
molecules  may  permanently  alter  their  relative  positions. 

In  the  liquid  state,  the  molecules  have  no  determinate 
positions  of  equilibrium.  They  may  rotate  completely  about 
their  centres  of  gravity,  and  may  also  move  forward  into  other 
positions.  But  the  repulsive  action  arising  from  the  motion 
is  not  strong  enough  to  overcome  the  mutual  attraction  of  the 
molecules  and  separate  them  completely  from  each  other.  A 
molecule  is  not  permanently  associated  with  its  neighbours, 
as  in  the  solid  state;  it  does  not  leave  them  spontaneously, 
but  only  under  the  influence  of  forces  exerted  upon  it  by 
other  molecules,  with  which  it  then  comes  into  the  same 
relation  as  with  the  former.  There  exists,  therefore,  in  the 
liquid  state,  a  vibratory,  rotatory  and  progressive  move- 
ment of  the  molecules,  but  so  regulated,  that  they  are  not 
thereby  forced  asunder,  but  remain  within  a  certain  volume 
without  exerting  any  outward  pressure. 

In  the  gaseous  state,  on  the  other  hand,  the  molecules  are 
removed  quite  beyond  the  sphere  of  their  mutual  attractions, 
and  travel  onward  in  straight  lines  according  to  the  ordinary 
laws  of  motion.  When  two  such  molecules  meet,  they  fly 
apart  from  each  other,  for  the  most  part,  with  a  velocity 
equal  to  that  with  which  they  came  togetlier.     The  perfection 

VOL.  II.  K  K 


454  DYNAMICAL  THEORY  OF  HEAT. 

of  the  gaseous  state,  however,  implies :  1.  That  the  space 
actually  occupied  by  the  molecules  of  the  gas  be  infinitely 
small  in  comparison  with  the  entire  volume  of  the  gas. 
2.  That  the  time  occupied  in  the  impact  of  a  molecule,  either 
against  another  molecule  or  against  the  sides  of  the  vessel,  be 
infinitely  small  in  comparison  with  the  interval  between  any 
two  impacts.  3.  That  the  influence  of  the  molecular  forces 
be  infinitely  small.  When  these  conditions  are  not  com- 
pletely fulfilled,  the  gas  partakes  more  or  less  of  the  nature 
of  a  liquid,  and  exhibits  certain  deviations  from  Gay-Lussac 
and  Mariotte's  laws.  Such  is,  indeed,  the  case  with  all 
known  gases ;  to  a  very  slight  extent  with  those  which  have 
not  yet  been  reduced  into  the  liquid  state ;  but  to  a  greater 
extent  with  vapours  and  condensable  gases,  especially  near 
the  points  of  condensation. 

Let  us  now  return  to  the  consideration  of  the  liquid  state. 
It  has  been  said  that  the  molecule  of  a  liquid,  when  it  leaves 
those  with  which  it  is  associated,  ultimately  takes  up  a 
similar  position  with  regard  to  other  molecules.  Tiiis,  how- 
ever, does  not  preclude  the  existence  of  considerable  irregu- 
larities in  the  actual  movements.  Now,  at  the  surface  of  the 
liquid,  it  may  happen  that  a  particle,  by  a  peculiar  combina- 
tion of  the  rectilinear,  rotatory,  and  vibratory  movements,  may 
be  projected  from  the  neighbouring  molecules  with  such  force 
as  to  throw  it  completely  out  of  their  sphere  of  action,  before 
its  projectile  velocity  can  be  annihilated  by  the  attractive 
force  which  they  exert  upon  it.  The  molecule  will  then 
be  driven  forward  into  the  space  above  the  liquid,  as  if  it 
belonged  to  a  gas,  and  that  space,  if  originally  empty,  will, 
in  consequence  of  the  action  just  described,  become  more 
and  more  filled  with  these  projected  molecules,  which  will 
comport  themselves  within  it  exactly  like  a  gas,  impinging 
and  exerting  pressure  upon  the  sides  of  the  envelope.  One 
of  these  sides,  however,  is  formed  by  the  surface  of  the 
liquid ;  and  when  a  molecule  impinges  upon  this  surface,  it 


DYNAMICAL  THEORY  OF  HEAT.  455 

will,  in  general,  not  be  driven  back,  but  retained  by  the 
attractive  forces  of  the  other  molecules.  A  state  of  equili- 
brium, not  static,  but  dynamic,  will  therefore  be  attained, 
when  the  number  of  molecules  projected  in  a  given  time 
into  the  space  above,  is  equal  to  the  number  which  in  the 
same  time  impinge  upon  and  are  retained  by  the  surface  of 
the  liquid.  This  is  the  process  of  vaporisation.  The  density 
of  the  vapour  required  to  ensure  the  compensation  just 
mentioned,  depends  upon  the  rate  at  which  the  particles  are 
projected  from  the  surface  of  the  liquid,  and  this  again  upon 
the  rapidity  of  their  movement  within  the  liquid,  that  is  to 
say,  upon  the  temperature.  It  is  clear,  therefore,  that  the 
density  of  a  saturated  vapour  must  increase  with  the  tem- 
perature. 

If  the  space  above  the  liquid  is  previously  filled  with  a  gas, 
the  molecules  of  this  gas  will  impinge  upon  the  surface  of  the 
liquid,  and  thereby  exert  pressure  upon  it ;  but  as  these  gas- 
molecules  occupy  but  an  extremely  small  proportion  of  the 
space  above  the  liquid,  the  particles  of  the  liquid  will  be  pro- 
jected into  that  space  almost  as  if  it  were  empty.  In  the 
middle  of  the  liquid,  however,  the  external  pressure  of  the 
gas  acts  in  a  different  manner.  There  also  it  may  happen 
that  the  molecules  may  be  separated  with  such  force  as  to 
produce  a  small  vacuum  in  the  midst  of  the  liquid.  But  this 
space  is  surrounded  on  all  sides  by  masses  which  afford  no 
passage  to  the  disturbed  molecules;  and  in  order  that  they 
may  increase  to  a  permanent  vapour-bubble,  the  number  of 
molecules  projected  from  the  inner  surface  of  the  vessel  must 
be  such  as  to  produce  a  pressure  outwards,  equal  to  the 
external  pressure  tending  to  compress  the  vapour-bubble. 
The  boiling  point  of  the  liquid  will,  therefore,  be  higher  as 
the  external  pressure  is  greater. 

According  to  this  view  of  the  process  of  vaporisation,  it  is 
possible  that  vapour  may  rise  from  a  solid  as  well  as  from  a 
liquid ;  but  it  by  no  means  necessarily  follows  that  vapour 

R  K    2 


456^  DYNAMICAL  THEORY  OF  HEAT. 

must  be  formed  from  all  bodies  at  all  temperatures.  The 
force  which  holds  together  the  molecules  of  a  body  may  be 
too  great  to  be  overcome  by  any  combination  of  molecular 
movements,  so  long  as  the  temperature  does  not  exceed  a 
certain  limit. 

The  production  and  consumption  of  heat  which  accompany 
changes  in  the  state  of  aggregation,  or  of  the  volume  of  bodies, 
are  easily  explained,  according  to  the  preceding  principles, 
by  taking  account  of  the  work  done  by  the  acting  forces. 
This  work  is  partly  external  to  the  body,  partly  internal  To 
consider  first  the  internal  work  : 

When  the  molecules  of  a  body  change  their  relative  posi- 
tions, the  change  may  take  place  either  in  accordance  with 
or  in  opposition  to  the  action  of  the  molecular  forces  existing 
within  the  body.  In  the  former  case,  the  molecules,  during 
the  passage  from  one  state  to  the  other,  have  a  certain 
velocity  imparted  to  them,  which  is  immediately  converted 
into  heat ;  in  the  latter  case,  the  velocity  of  their  movement, 
and  consequently  the  temperature  of  the  body,  is  diminished. 
In  the  passage  from  the  solid  to  the  liquid  state,  the  mole- 
cules, although  not  removed  from  the  spheres  of  their  mutual 
attractions,  nevertheless  change  their  relative  positions  in 
opposition  to  the  molecular  forces,  which  forces  have, 
therefore,  to  be  overcome.  In  evaporation,  a  certain  number 
of  the  molecules  are  completely  separated  from  the  remainder, 
which  again  implies  the  overcoming  of  opposing  forces.  In 
both  cases,  therefore,  work  is  done,  and  a  certain  portion  of 
the  vis  viva  of  the  molecules,  that  is,  of  the  heat  of  the  body, 
is  lost.  But  when  once  the  perfect  gaseous  state  is  attained, 
the  molecular  forces  are  completely  overcome,  and  any- 
further  expansion  may  take  place  without  internal  work, 
and,  therefore,  without  loss  of  heat,  provided  there  is  no 
external  resistance. 

But  in  nearly  all  cases  of  change  of  state  or  volume,  there 
is  a  certain  amount  of  external  resistance  to  be  overcoiue. 


POLARISATION   OP   LIGHT.  457 

and  a  corresponding  loss  of  heat.  When  the  pressure  of  a 
gas,  that  is  to  say,  the  impact  of  its  atoms,  is  exerted  against 
a  movable  obstacle,  such  as  a  piston,  the  molecules  lose  just 
so  much  of  their  moving  power  as  they  have  imparted  to  the 
piston,  and,  consequently,  their  velocity  is  diminished  and 
the  temperature  lowered.  On  the  contrary,  when  a  gas  is 
compressed  by  the  motion  of  a  piston,  its  molecules  are 
driven  back  with  greater  velocity  than  that  with  which  they 
impinged  on  the  piston,  and,  consequently,  the  temperature 
of  the  gas  is  raised. 

When  a  liquid  is  converted  into  vapour,  the  molecules 
have  to  overcome  the  atmospheric  pressure  or  other  external 
resistance,  and,  in  consequence  of  this,  together  with  the 
internal  work  already  spoken  of,  a  large  quantity  of  heat 
disappears,  or  is  rendered  latent,  the  quantity  thus  consumed 
being  to  a  considerable  extent  affected  by  the  external  pres- 
sure. The  liquefaction  of  a  solid  not  being  attended  with 
much  increase  of  volume,  involves  but  little  work ;  never- 
theless, the  atmospheric  pressure  does  influence,  in  a  slight 
amount,  both  the  latent  heat  of  fusion  and  the  melting 
point. 


LIGHT. 


POLARISATION. 


The  phenomena  of  circular  polarisation  have  lately  ac- 
quired so  much  importance  in  chemistry,  as  to  make  it  highly 
necessary  for  the  student  to  be  acquainted  with  them.  But 
to  render  a  description  of  these  phenomena  intelligible,  a 
a  few  elementary  explanations  of  the  subject  of  polarisation 
in  general  must  first  be  offered. 

Suppose  a  ray  of  light,  A  C  (fig.  24),  to  fall  upon  a  plate 

K  K    3 


458 


POLARISATION   OF   LIGHT. 


of  glass  (not  silvered,  but  blackened  at  the  lower  surface)  at 
C,  making  an  angle  of  54^°  with  the  normal  P  C,  or  35^° 

Fig.  24. 


with  the  reflecting  surface.  This  ray  will  be  reflected  in  tho 
direction  C  D,  making  an  angle  P  C  D  =  A  C  P,  and  in  the 
same  plane  as  A  C  and  C  P.  Now  suppose  the  reflected  rajr 
to  fall  upon  a  second  surface  of  glass  at  the  same  angle  of 
54^°  with  the  normal.  If,  then,  the  second  mirror  be  so 
placed,  that  its  plane  of  reflection  is  parallel  to  the  plane  of 
reflection  from  the  first  surface  (see  left-hand  figure),  then 
the  ray  will  be  reflected  from  the  second  surface  in  the 
direction  D  E,  just  as  if  it  proceeded  directly  from  a  luminous 
source,  and  had  not  undergone  previous  reflection;  but  if 
the  second  mirror  be  so  adjusted  that  its  plane  of  reflection 
is  perpendicular  to  that  of  the  first  (see  right-hand  figure), 
then  the  ray,  CD,  will  not  be  reflected  from  it  at  all.  In 
intermediate  positions,  still  at  the  same  angle  of  incidence, 
the  ray,  C  D,  will  be  partially  reflected,  the  quantity  of  light 
in  the  reflected  ray,  D  E,  being  greater  as  the  planes  of 
reflection  of  the  two  mirrors  are  more  nearly  parallel. 

The  ray,  after  reflection  from  glass  at  an  angle  of  54-|-*' 
appears  then  to  exhibit  difi'erent  properties,  according  to  the 
direction  in  which  it  is  a  second  time  reflected;  one  side  of 
the  ray  appearing  to  be  reflectible,  and  the  other  side  not  so. 
The  ray  has  now  different  properties  on  different  sides,  and 
is  said  to  be  polarised. 

The  angle,  54^°,  is  called  the  polarising  angle  for  glass. 


POLARISATION   OF    LIGHT.  459 

For  every  medium  there  is  a  particular  polarising  angle,  the 
magnitude  of  which  depends  upon  the  refracting  power  of 
the  medium.*  Now,  as  the  different  coloured  rajs  which 
compose  white  light,  differ  in  refrangibility  (i.  104),  there  must 
be  for  each  coloured  ray  a  distinct  polarising  angle.  Hence 
it  is  evident  that  only  homogeneous  light  can  be  completely 
polarised  by  reflection.  Solar  light,  or  ordinary  gas  or 
candle-light,  can  never  be  made  to  disappear  completely  in 
the  manner  above  mentioned. 

The  plane  in  which  a  polarised  ray  is  most  easily  reflected 
is  called  its  plane  of  polarisation :  it  coincides  with  the 
plane  of  reflection  (or  of  incidence). 

Light  is  also  polarised  by  refraction,  and  the  refracted  ray 
is  polarised  in  a  plane  perpendicular  to  the  plane  of  refrac- 
tion, or  of  incidence,  and,  therefore,  also  perpendicular  to  the 
plane  of  polarisation  of  the  reflected  ray ;  so  that  it  would  be 
reflected  from  a  surface  of  glass  at  an  angle  of  54^°,  just 
under  the  circumstances  in  which  the  ray  polarised  by  re- 
flection would  not.  Light,  however,  is  never  completely 
polarised  by  one  refraction ;  but  by  successive  refractions 
through  a  number  of  surfaces  of  glass,  or  other  medium, 
it  may  be  brought  within  any  assigned  limit  of  complete 
polarisation. 

*  In  all  cases,  the  polarisinfr  angle,  A  C  P  (fig.  25),  is  that  for  which  the 
refracted  ray,  C  D,  is  perpendicular  to  the  reflected  ray,  C  B.  Let  m  denote 
the  index  of  refraction,  then : 

m  =  ""^  AC  P.  Fig.  25. 

sin  qciV 

but  angle  A.C  P  =  B  CP  [=  0]  ;  and 
since  B  C  is  perpendicular  to  C  D,  and  QC 
to  CN,  angle  QCD  =  BCN  =  90°  -  e  ; 
therefore 

cosO 
that  is  to  say,  the  polarising  avgle  is  t/ie 
angle  whose  tanyent  is  equal  to  the  index 
of  refraction. 

K  K    4 


46U  POLARISATION    OF    LIGHT. 

All  crystalline  bodies  not  belonging  to  the  regular  system, 
possess  the  power  of  double  refraction  (i.  103),  that  is  to  say, 
a  ray  of  light  entering  such  a  medium  is  split  up  into  two 
rays  of  equal  intensity,  which  traverse  the  crystal  in  different 
directions.  In  all  such  media,  however,  there  are  either 
one  or  two  directions  in  which  double  refraction  does  not 
take  place,  and  these  lines  are  called  the  optic  axes  of  the 
crystal.  Transparent  calcspar,  or  Iceland  spar,  which  crys- 
tallises in  rhombohedrons,  and  exhibits  double  refraction 
more  distinctly  than  any  other  substance,  is  a  crystal  with 
one  optic  axis,  the  direction  of  that  axis  being  parallel  to 
the  line  joining  the  obtuse  summits  of  the  rhomb.  A  ray 
traversing  the  crystal  in  a  direction  parallel  to  this  axis  is  not 
divided  into  two ;  but  in  all  other  directions  the  ray  is  doubly 
refracted  ;  and  the  two  rays  into  which  it  is  thus  divided  are 
both  completely  polarised,  the  one  in  the  principal  section, 
that  is  to  say,  in  a  plane  passing  through  the  optic  axis  and 
the  direction  in  which  the  ray  traverses  the  crystal ;  the 
other  at  right  angles  to  that  plane.  The  ray  which  is 
polarised  in  the  principal  section  follows  the  ordinary  laws 
of  refraction,  remaining  always  in  the  plane  of  incidence,  and 
having  for  all  incidences  a  constant  index  of  refraction ;  but 
the  ray  polarised  perpendicularly  to  the  principal  section 
follows  different  laws  of  refraction,  its  direction  not  being 
confined  within  the  plane  of  incidence,  unless  that  plane  coin- 
cides with  or  is  perpendicular  to  the  principal  section,  and 
its  index  of  refraction,  excepting  in  the  last-mentioned  case, 
varying  continually  with  the  angle  of  incidence.  The  former 
of  these  rays  is  called  the  ordinaryy  the  latter  the  extra- 
ordinary ray. 

When  these  two  oppositely  polarised  rays  fall  on  a  plate 
of  glass  at  the  angle  of  54^-°,  so  placed  that  the  plane  of 
reflection  is  parallel  to  the  principal  section  of  the  crystal,  the 
ordinary  ray  is  reflected,  and  the  extraordinary  ray  is  not, 
the  contrary  effect  taking  place  when  these  planes  are  at 


POLARISATION   OP   LIGHT. 


461 


right  angles  to  each  other.  When  the  plane  of  reflection  is 
inclined  to  the  principal  section  at  any  angle  between  0°  and 
90°,  both  rays  are  reflected,  but  with  diff*erent  intensities. 

NichoVs  Prism, — It  is  often  desirable  to  get  rid  of  one  of 
the  images  produced  by  a  double-refracting  crystal.  This  is 
efi*ected  by  the  arrangement  shown  in  ^''S-  26. 

fig.  26,  which  consists  of  two  similar 
prisms  of  calcspar,  A  B  C  D,  C  D  E  F,  ce- 
mented together  with  Canada  balsam  at 
the  faces,  C  D.  The  faces,  A  B,  E  F,  are 
cut  so  as  to  make  an  angle  of  68°  with 
the  obtuse  edges,  A  E,  B  F,  of  the  na- 
tural crystal  (the  natural  faces  make  an 
angle  of  71°  with  the  obtuse  edges),  and 
the  faces,  C  D,  are  perpendicular  to  A  B 
and  E  F.  With  this  arrangement,  it  is 
found  that  of  the  two  rays,  no,  ne,  into 
which  an  incident  ray,  m  n,  is  divided, 
the  ordinary  ray,  n  o,  on  reaching  the 
surface  of  Canada  balsam  (whose  index 
of  refraction  is  less  than  that  of  the 
ordinary  and  greater  than  that  of  the 
extraordinary  ray),  suffers  total  reflection 
in  the  direction  o  P,  while  the  extraordinary  ray  passes  on 
in  the  direction  ef,  and  emerges  in/^,  parallel  to  m  n.  An  eye 
placed  at  /,  therefore,  sees  but  one  image,  viz.,  that  formed  by 
the  extraordinary  ray.  This  apparatus,  called  a  Nichol's  prism, 
is  of  great  use  in  experiments  with  polarised  light.  For,  as 
it  transmits  only  the  extraordinary  ray,  a  beam  of  ordinary 
light  passing  through  it  will  be  polarised  in  a  plane  perpen- 
dicular to  the  principal  section — that  is  to  Fig.  27. 
say,  to  the  shorter  diagonal  of  the  rhomb,  ab  ^ 
(fig.  27);  and  a  ray,  already  polarised,  will 
be  stopped  by  the  prism  if  its  plane  of  polari- 
sation is  parallel  to  a  b,  but  will  pass  freely 


462  POLARISATION    OF    LIGHT. 

through  it  when  the  plane  of  polarisation  is  perpendicular  to 
ah,  or  parallel  to  the  longer  diagonal,  cd.  Hence,  also, 
two  NichoPs  prisms,  placed  one  behind  the  other,  appear 
perfectly  opaque  when  their  principal  sections  are  at  right 
angles  to  each  other,  perfectly  transparent  when  the  principal 
sections  are  parallel,  and  transmit  light  with  diminished  inten- 
sity in  intermediate  positions. 

Polarisaiion  hy  Tourmalines.  —  The  tourmaline,  which  is 
a  crystallised  mineral  having  one  optic  axis,  possesses  the 
remarkable  property  of  transmitting  liglit  only  when  polar- 
ised in  a  plane  perpendicular  to  that  axis.  Hence,  a  plate  of 
tourmaline  cut  with  faces  parallel  to  the  optic  axis,  acts 
exactly  like  a  Nichol's  prism,  and  may  be  used  in  the  same 
manner.  It  is,  however,  less  convenient,  on  account  of 
its  colour,  which,  in  the  best  tourmalines,  is  rather  a  dark 
yellow-brown. 

Nature  of  Polarised  Light, — Light  is  supposed  to  consist 
of  undulations  excited  in  an  ethereal  medium  pervading  all 
space,  and  filling  up  the  intervals  between  the  particles  of 
ponderable  bodies.  Moreover,  the  particles  of  this  ether  are 
supposed  to  vibrate,  not  in  the  direction  of  the  ray,  like  the 
particles  of  air  in  conveying  sound,  but  in  planes  at  right 
angles  to  the  length  of  the  ray,  like  the  transverse  vibrations 
of  a  stretched  cord. 

Further,  the  difference   between  ordinary   and   polarised 
light,  is  supposed  to  be  this ;    that  in  the  former,  the  particles 
Fig.  28.  of  the  ether  vibrate  in  all  imagi- 

nable directions,  at  right  angles, 
to  the  length  of  the  ray ;  while, 
in  the  latter,  they  are  confined  to 
one  particular  plane.  Thus,  if  A 
(fig.  28)  represents  the  projection 
of  an  unpolarised  ray,  travelling 
at  right  angles  to  the  plane  of  the 
paper,  the  particles  of  the  ether  at 


POLARISATION   OF   LIGHT.  463 

all  points  of  this  ray  vibrate  parallel  to  the  plane  of  the  paper, 
but  some  may  move  in  the  direction  a  a',  others  in  h  b',  c  c\ 
d  df,  &c.  Now  imagine  all  these  vibrations  to  be  reduced  to 
one  plane,  in  the  direction  a  a',  for  example.  Then  the  ray 
will  become  polarised.  In  fact,  since  its  particles  now  vibrate 
in  one  direction  only,  it  is  no  longer  a  matter  of  indifference 
whether  the  ray  is  presented  to  a  reflecting  surface  on  one 
side  or  the  other ;  whereas  the  unpolarised  ray,  whose  particles 
vibrate  in  all  directions,  will  be  reflected  in  the  same  manner 
on  whichever  side  it  meets  the  surface  of  any  medium. 

Now,  from  considerations  into  which  we  cannot  at  present 
enter,  it  is  found  that  a  plate  of  tourmaline  transmits  only 
those  vibrations  which  are  parallel  to  its  axis.  Since  then,  a 
ray  of  polarised  light  is  transmitted  through  a  tourmaline 
only  when  its  plane  of  polarisation  is  perpendicular  to  the 
axis  of  the  tourmaline  (p.  461),  it  follows  that  the  plane  of 
polarisation  of  the  ray  is  perpendicular  to  the  plane  of  vibration. 
Hence,  also,  the  plane  of  vibration  of  a  ray  polarised  by 
reflection  is  at  right  angles  to  the  plane  of  incidence  (or  of 
reflection) ;  the  plane  of  vibration  of  a  ray  polarised  by 
refraction  is  parallel  to  the  plane  of  incidence ;  and  of  the 
two  rays  into  which  a  beam  of  light  is  divided  by  double  re- 
fraction through  a  rhomb  of  calcspar,  the  ordinary  ray  vibrates 
at  right  angles  to  the  principal  section,  and  the  extraordinary 
ray  parallel  to  that  section.  The  vibrations  of  a  ray  polarised 
by  passing  through  a  Nichol's 
prism,  are,  therefore,  parallel  to 
to  the  principal  section,  that  is,  to 
the  shorter  diagonal  of  the  prism 
(fig.  27). 

Let  mn  (fig.  29),  be  the  plane 
of  vibration  of  a  polarised  ray 
moving  at  right  angles  to  the 
plane  of  the  paper,  and  meeting  it 
at  the  point  a.    If  this  ray  enters 


464  CIRCULAR   POLARISATION. 

a  plate  of  tourmaline,  whose  axis  is  parallel  to  m  n,  or  a 
Nicbol's  prism,  whose  principal  section  is  in  that  direction, 
the  ray  will  be  transmitted  with  its  full  intensity.  But  if 
the  axis  of  the  tourmaline  or  the  principal  section  of  the 
prism  be  turned  round  into  the  position  rnfii',  the  intensity 
of  the  transmitted  light  will  be  diminished,  because  the 
tourmaline  or  the  prism  will  only  transmit  vibrations  in  the 
direction  a  m,  and  there  is  always  a  loss  of  power  in  changing 
the  direction  of  motion.  Let  ah  represent  the  utmost 
length  of  the  excursion  of  a  particle  of  the  ether  in  the 
original  direction  of  vibration,  in  other  words,  the  original 
intensity  of  the  light.  Draw  i  c  at  right  angles  to  a  m' ;  then 
a  c  represents  the  component  of  the  force  a  b  in  the  direction 
a  m',  and  a  c  is  clearly  less  than  a  b.  If  the  tourmaline  or 
the  prism  be  turned  still  further  into  the  position  m''  w''  the 
reduced  portion  of  the  intensity  a  c'  will  be  found  to  be  still 
less;  and,  lastly,  when  the  axis  or  the  principal  section  is 
perpendicular  to  mw,  the  reduced  portion  of  the  motion 
becomes  equal  to  nothing,  and  there  is  no  light  transmitted. 
Generally,  if  u  be  the  original  intensity  of  the  light,  and 
6  the  angle  between  the  old  and  new  planes  of  vibration, 
the  reduced  intensity  will  be  u  cos  6. 

Circular  Polarisation. — Some  media  possess  the  singular 
property  of  changing  the  direction  of  vibration  of  a  ray  of 
polarised  light ;  in  other  words,  of  causing  the  plane  of  pola- 
risation to  rotate  through  a  certain  angle,  either  to  the 
right  or  to  the  left.  This  property  is  exhibited  in  a  remark- 
able degree,  by  quartz  or  rock-crystal,  a  mineral  which 
crystallises  in  six-sided  prisms  terminated  by  six-sided  pyra- 
mids, the  axis  being  a  straight  line  joining  the  two  pyramidal 
summits.  Suppose  now,  a  ray  polarised  by  passing  through 
a  Nichol's  prism  to  be  viewed  through  another  such  prism, 
having  its  principal  section  at  right  angles  to  that  of  the 
first.  The  field  will,  of  course,  appear  dark.  Then  let 
a  plate  of  quartz,  bounded  by  parallel  faces  cut  perpen- 
dicularly to  its  axis,  be  interposed  between  tlie  two  prisms. 


CIRCULAR   POLARISATION.  465 

Immediately  the  field  of  view  will  appear  brilliantly  illumi- 
nated and  coloured,  exliibiting  a  tint  of  red,  yellow,  green, 
blue,  &c.,  according  to  the  thickness  of  the  quartz-plate. 
If  the  Nichol's  prism,  which  serves  as  the  eye-piece,  be 
turned  on  its  axis,  the  colours  will  go  through  the  regular 
prismatic  series,  from  red  to  violet,  or  the  contrary,  according 
to  the  direction  of  rotation;  but  no  alteration  of  colour  is 
produced  by  rotating  the  quartz-plate  while  the  eye-piece 
remains  stationary.  Exactly  similar  effects  are  produced  if 
either  of  the  Nichol's  prisms  be  replaced  by  a  tourmaline  or 
a  glass  reflector,  or  a  bundle  of  glass  plates  which  polarise 
by  ordinary  refraction ;  but  the  two  NichoPs  prisms  form  by 
far  the  most  convenient  apparatus,  and  we  shall  therefore 
suppose  them  to  be  always  used.  For  distinction,  the  one 
is  called  the  polarising  prism  or  polariser,  the  other,  the 
eye-piece. 

To  understand  the  phenomena  just  described,  we  must 
examine  what  takes  place  when  homogeneous  light  is  used. 
Suppose,  then,  a  plate  of  dark-red  glass  coloured  with  red 
oxide  of  copper,  to  be  interposed  anywhere  between  the  two 
prisms  placed  as  before,  with  their  principal  sections  at  right 
angles,  so  that  no  light  is  transmitted  by  the  eye-piece.  On 
interposing  the  plate  of  quartz,  a  red  light  immediately 
makes  its  appearance,  and,  to  render  the  field  again  dark,  it 
is  necessary  to  turn  the  eye-piece  through  a  certain  angle, 
either  to  the  right  or  to  the  left.  Now,  as  the  Nichol's 
prism  stops  a  ray  of  light  only  when  the  plane  of  vibration 
of  that  ray  is  perpendicular  to  its  principal  section,  it  follows 
that  the  ray  which  has  traversed  the  quartz  must  have  had 
its  plane  of  vibration  thereby  deflected  through  an  angle 
equal  to  that  through  which  the  eye-piece  has  been  moved. 
This  effect  is  called  circular  polarisation. 

Precisely  similar  effects  are  produced  with  yellow,  green, 
violet,  or  any  other  kind  of  homogeneous  light;  but  the 
angle  of  rotation  varies  according  to  the  nature  of  the  ray, 
being  least  for  red,  and  greatest  for  violet  light. 


466 


CIRCULAR   POLARISATION. 


Some  crystals  of  quartz  rotate  the  plane  of  polarisation  of 
a  ray  to  the  right,  others  to  the  left ;  the  former  are  called 
right-handed,  the  latter  left-handed  quartz.  But  in  whichever 
direction  the  rotation  takes  place,  a  plate  of  quartz  of  given 
thickness  always  produces  the  same  amount  of  angular 
deviation  for  a  ray  of  given  refrangibility ;  and  for  plates  of 
different  thickness,  the  deviation  for  any  particular  ray 
increases  in  direct  proportion  to  the  thickness.  The  following 
table  gives  the  angles  of  deviation  for  the  principal  rays  of 
the  spectrum  produced  by  plates  of  quartz  of  the  thickness  of 
1  millimeter  and  3*75  millimeters. 


Angle  of  Rotation. 

Colour*. 

Plate 

Plate 

1  mm.  thick. 

3-75  mm.  thick. 

Medium  red      .... 

15° 

.561° 

„        orange 

19 

71i 

„        yellow 

24 

90 

green 

27 

101] 

blue    . 

32 

120 

„        indigo 

38 

142^ 

„        violet  . 

44 

165 

Fig.  30. 


We  can  now  explain  the  succession  of  colours  produced 
when  ordinary  daylight   is  used.     Suppose  a  beam  of  white 

light,  polarised  by  a  Nichol's 
prism,  whose  principal  section  is 
parallel  to  A  A'  (fig.  30  ),  to 
pass  through  a  plate  of  right- 
handed  quartz,  3*75  mm.  thick. 
The  vibrations  of  the  several 
coloured  rays  composing  the 
beam  of  polarised  light,  are  all 
at  first  parallel  to  A  A' ;  but 
by  passing  through  the  quartz, 
their  planes  of  vibration  are 
deflected  through  the  several 
angles  given  in  the  above  table, 


CIRCULAR   POLARISATION.  467 

the  red  ray  then  vibrating  in  the  line  rv',  the  yellow  in  yy, 
the  violet  in  v  v',  &c.  Now,  let  the  ray  be  viewed  through 
another  Nichol's  prism,  placed  with  its  principal  section  also 
parallel  to  A  A' ;  then,  by  reference  to  the  explanation  given 
at  page  463,  it  will  be  seen  that  the  red  and  violet  rays  w^ill 
be  transmitted  with  but  slightly  diminished  intensity,  the 
orange  and  blue  with  less,  the  yellow  with  still  less,  and  the 
green  not  at  all.  The  result  will,  therefore,  be  a  purple 
tint.  Now  let  the  eye-piece  be  turned  from  left  to  right. 
As  the  principal  section  passes  successively  over  the  lines 
rr,  oo\  &c.,  the  red,  orange,  yellow,  &c.,  will,  in  suc- 
cession, be  more  fully  transmitted  than  the  other  rays,  so 
that  a  succession  of  tints  will  be  produced  agreeing  nearly 
with  the  colours  of  the  spectrum  and  following  in  the  same 
order,  from  red  through  yellow  to  violet.  If  the  eye-piece 
be  turned  the  contrary  w^ay,  the  order  of  the  tints  will  be 
reversed.  If  the  quartz  were  left-handed,  the  phenomena 
would  be  precisely  similar,  excepting  that  the  colours  would 
change  from  red  through  yellow  to  violet,  when  the  eye-piece 
was  turned  from  right  to  left. 

Similar  changes  of  colour  will  be  produced  with  a  plate 
of  quartz  of  any  other  thickness ;  but  the  tint  produced  at 
any  given  inclination  of  the  polariser  and  eye-piece,  will  of 
course  be  different. 

The  tint  produced  with  a  quartz-plate  S'15  mm.  thick, 
when  the  prncipal  sections  of  the  polariser  and  eye-piece 
are  parallel  to  one  another,  deserves  particular  notice. 
This  tint,  as  already  observed,  is  a  purple,  and  more- 
over changes  ver}^  quickly  to  red  or  to  violet,  when  the  eye- 
piece is  turned  one  way  or  the  other,  the  change  of  colour 
thus  produced  being,  in  fact,  very  much  more  rapid  and  de- 
cided than  in  any  other  part  of  the  circuit.  It  is  accordingly 
distinguished  by  the  term  sensitive  tint,  or  transition-tint 
{couleur  sensible,  teinte  de  passage).  On  account  of  the  facility 
and  certainty  with  which  it  may  be  recognised,  it  is  frequently 


468  CIRCULAR   POLARISATION. 

adopted  as  the  standard  tint  in  measuring  the  angles  of 
rotation  produced  by  different  substances  ;  it  is,  in  fact,  much 
easier  to  determine  when  this  particular  colour  makes  its  ap- 
pearance, than  to  seize  the  exact  moment  when  a  ray  of  red, 
yellow,  or  other  homogeneous  light  completely  disappears. 

The  rotatory  power  of  quartz  is  essentially  related  to  its 
crystalline  forml  It  is  not  exhibited  by  opal,  or  any  other 
amorphous  variety  of  silica,  or  by  silica  dissolved  in  potash 
or  fused  by  the  oxy-hydrogen  blowpipe.  The  same  is  true 
with  regard  to  a  few  other  inorganic  compounds  possessing 
the  rotatory  power,  viz.  chlorate  of  soda,  bromate  of  soda, 
and  acetate  of  uranic  oxide  and  soda  ;  these  salts  exhibiting 
that  power  only  when  crystallised,  not  in  solution. 

Circular  Polarisation  in  Organic  Bodies. — The  power  of 
rotating  the  plane  of  vibration  of  a  polarised  ray,  is  much 
more  widely  diffused  in  the  organic,  than  in  the  inorganic 
world ;  moreover,  inorganic  bodies  possess  it  in  the  liqui4> 
as  well  as  in  the  crystalline  state.  Among  organic  compounds 
which  rotate  the  plane  of  polarisation  to  the  right,  may  be  men- 
tioned: —  Cane-sugar,  grape-sugar,  diabetic  sugar, milk-sugar, 
dextrin,  camphor,  asparagin,  cinchonine,  quinidine,  narcotine, 
tartaric  acid,  camphoric  acid,  aspartic  acid,  oil  of  lemons, 
castor-oil,  croton-oil.  The  following  rotate  to  the  left: — 
uncrystallisable  sugar  of  fruits,  starch,  albumen,  amygdalin, 
quinine,  nicotine,  strychnine,  brucine,  morphine,  codeine,  malic 
acid,  anti-tartaric  acid,  oil  of  turpentine,  oil  of  valerian. 

By  passing  a  polarised  ray  through  tubes  of  different 
lengths,  filled  with  the  same  solution  of  cane-sugar,  or  other 
rotatory  substance,  it  is  found  that  the  angle  of  deviation  is 
proportional  to  the  length  of  the  column  of  liquid ;  and,  by 
filling  the  same  tube  with  solutions  containing  different  quan- 
tities of  sugar,  &c.,  it  is  found  that  the  angle  of  deviation  is 
proportional  to  the  quantity  of  the  substance  contained  in  a 
column  of  given  length.  Generally,  then,  the  angle  of 
deviation  is  proportionate  to  the  number  of  active  particles 
which  the  light  has  to  pass. 


CIRCULAR   POLARISATION.  469 

If,  then,  s  be  the  quantity  of  active  substance  contained  in 
a  unit  of  weight  of  the  solution,  I  the  length  of  the  column, 
and  a  the  observed  angle  of  rotation  for  a  particular  tint, 
the  transition-tint,  for  example,  the  angle  of  rotation  for  the 
unit  of  length,  and  supposing  the  entire  column  to  be  filled 

with  the  optically  active  substance,  will  be  — -.      But  as  the 

solution  of  a  substance  is  often  attended  with  condensation  of 
volume,  it  is  best,  in  order  to  obtain  a  measure  of  the 
rotatory  power,  independent  of  such  irregularities,  to  refer 
the   observed  angle  of  deviation  to  a  hypothetical   unit  of 

density,  that  is  to  say,  to  divide  the  quantitv by  the 

"     s  I 

density  8  of  the  solution.  The  fraction  thus  obtained,  viz., 
[a]  =  — ttj  is  called  the  specific  rotatory  'power,  and  expresses 

the  angle  of  rotation  which  the  pure  substance  in  a  column 
of  the  unit  of  length  and  density  =  1  would  impart  to  the  ray 
corresponding  to  the  transition-tint.  For  example,  a  solution 
containing  155  milligrammes  of  cane-sugar  in  a  gramme  of 
liquid,  has  a  specific  gravity  =  1  '06,  and  deflects  the  tran- 
sition-tint by  24°,  in  a  column  20  centimeters  long ;  its  specific 
rotatory  power  is  therefore  — 

[a]  = '^ 7-3° 

^  ^       0-155  .  20  .  106 

Saccharimetry,  —  An  important  practical  application  of  the 
principles  just  explained  relates  to  the  determination  of  the 
quantity  of  sugar  contained  in  saccharine  solutions.  The 
apparatus  used  for  this  purpose  consists  of  a  glass  tube 
(fig.  31),  surrounded  with  a  case  of  wood  or  brass,  and  closed 

Fig.  31. 


at  both  ends  with  plate-glass  discs  ground  to  fit  water-tight 

VOL.  II.  L  L 


470 


CIRCULAR  POLARISATION. 


and  pressed  against  the  tube  by  mOans  of  screw-caps.  The 
tube  being  completely  filled  with  the  liquid,  is  placed  on  the 
supports,  cd  (fig.  32),  between  two  Nichol's  prisms,  one 
of  which,  A,  serves  as  a  polariser,  the  other,  B,  as  an  eye- 
piece.     The  latter  carries  a  vernier,  7n,  moving  round  a 

Fig.  32. 


graduated  circle.  The  simplest  way  of  using  this  apparatus 
is  to  interpose  between  the  tube  and  the  polariser  a  glass 
coloured  with  sub-oxide  of  copper,  the  tint  of  which  corre- 
sponds with  the  red  of  the  fixed  line  C  of  the  spectrum — 
and  having  set  the  eye-piece  with  its  principal  section  at 
right  angles  to  that  of  the  polariser  (which  makes  the  field  of 
view  dark  so  long  as  the  tube  is  not  interposed),  to  adjust 
the  tube  in  its  place,  and  turn  the  eye-piece  round  till  the 
red  light  completely  disappears.  The  angle  through  which 
the  eye-piece  is  turned  measures  the  deviation  produced  by 
the  saccharine  liquid. 

A  solution  of  164*71  grammes  of  pure  and  dry  cane-sugar 
in  a  litre  of  water,  produces  in  a  tube,  20  centimeters  long. 


^ 


CIRCULAR  POLARISATION.  471 

an  optical  effect  equal  to  that  of  a  plate  of  right-handed 
quartz,  1  millimeter  thick,  that  is  to  say,  it  turns  the  plane  of 
polarisation  of  the  red  ray  corresponding  to  the  fixed  line  C, 
through  an  angle  of  15*3°.  Hence,  if  any  other  solution  of 
cane-sugar  in  a  tube  of  the  same  length  produces  a  deviation 
of  a  degrees,  one  litre  of  that  solution  will  contain 

.  164*71  grammes  of  sugar. 

lO'o 

The  direct  measurement  of  the  rotation  of  the  red  ray  is, 
however,  by  no  means  the  best  mode  of  observation,  because, 
as  already  observed  (p.  468),  it  is  difficult  to  tell  with  pre- 
cision when  the  light  completely  disappears.  For  this  reason 
it  is  better  to  introduce  behind  the  polarising  prism,  instead 
of  the  red  glass,  a  plate  of  quartz  3*75  millimeters  thick, 
which,  when  the  polariser  and  eye-piece  are  set  with  their 
principal  sections  parallel,  exhibits  the  transition-tint  The 
interposition  of  the  saccharine  liquid,  which  rotates  to  the 
right,  causes  this  tint  to  change ;  and  the  rotation  is  measured 
by  the  number  of  degrees  through  which  the  prism  must  be 
turned  to  restore  the  transition-tint. 

Greater  exactness  is  obtained  by  using  a  double  plate  of 
quartz  3*75  millimeters  thick,  one-half  being  composed  of 
right-handed,  the  other  half  of  left-handed  quartz.  •  Such  a 
plate  will  exhibit  the  transition-tint  with  perfect  uniformity 
on  both  halves,  when  the  polariser  and  eye-piece  are  set  with 
their  principal  sections  parallel ;  but  on  turning  the  eye-piece 
to  the  right,  one-half  of  the  plate  will  incline  to  red,  and  the 
other  to  blue.  The  same  change  will,  of  course,  take  place 
on  introducing  the  tube  containing  the  saccharine  liquid ; 
and  to  restore  the  uniformity  of  tint,  the  eye-piece  must  be 
turned  a  certain  number  of  degrees  the  contrary  way.  If  the 
liquid  has  but  a  slight  rotatory  power,  this  method  is  quite 
satisfactory ;  but  if  the  rotatory  power  is  considerable,  an 

LL  2 


472  CIRCULAR  POLARISATION. 

error  arises  from  the  different  angles  of  rotation  imparted  to 
the  different  coloured  rays. 

To  obviate  this  last  source  of  inaccuracy,  a  contrivance^ 
called  the  compensatory  has  been  invented.  It  consists  of  two 
prismatic  plates  of  quartz,  r/  (fig.  33),  having  their  faces, 


>"''|""""".miM!mi:iiiiimii'niiiiii 


c  c',  perpendicular  to  the  crystallographic  axis,  and  the  oppo- 
site faces  inclined  to  this  axis  at  equal  angles.  These  prisms 
are  introduced  into  the  polarising  apparatus  between  the  tube 
and  the  eye-piece,  and  one  of  them  is  made  to  slide  over  the 
other  by  means  of  a  rack  and  pinion,  so  that  the  two  together 
form  a  plate  of  variable  thickness.  To  the  frame  of  one  of 
these  prisms  is  attached  a  linear  scale,  a  h,  and  to  the  other 
an  index,  or  a  vernier,  v  v'.  One  hundred  divisions  of  the 
scale  correspond  to  an  increase  of  1  millimeter  in  the  thick- 
ness of  the  compound  plate.  Suppose  now  these  two  prisms 
to  consist  of  left-handed  quartz  ;  a  flat  plate  of  right-handed 
quartz,  whose  thickness  is  equal  to  that  of  the  two  compen- 
sating prisms  together  when  the  index  points  to  0°,  is  likewise 
introduced  between  the  tube  and  the  eye-piece.  This  plate 
then  completely  neutralises  the  action  of  the  compensator, 
and  the  effect  is  the  same  as  if  neither  the  compensator 
nor  the  plate  of  right-handed  quartz  were  introduced,  the 
double  quartz-plate  (p.  471)  still  exhibiting  the  transition- 
tint  on  its  two  halves,  when  the  tube  containing  the  saccha- 
rine solution  is  not  in  its  place.  Now  let  the  tube  containing 
the  dextro-rotatory  saccharine  liquid  be  introduced.  Imme- 
diately the  two  halves  of  the  double-plate  assume  different 


CIRCULAR  POLARISATIOlSr.  473 

colours ;  and  to  restore  the  uniformity  of  tint,  the  compensator 
must  be  shifted  so  as  to  give  the  combined  left-handed  prisms 
a  greater  thickness.  Suppose  that,  to  produce  this  compen- 
sation, the  index  is  moved  through  eighteen  divisions  of  the 
scale.  Then  the  rotatory  action  of  the  liquid  in  the  tube  is 
equal  to  that  of  a  quartz-plate  having  a  thickness  of  -^^  of 
a  millimeter,  that  is  to  say,  it  turns  the  red  ray  through  an 
angle  of  15-3°  x  -^\  =  2f . 

.  In  order  that  the  preceding  method  may  be  directly  applied 
to  determine  the  strength  of  a  solution  of  any  optically  active 
substance,  it  is  necessary :  1.  That  the  solution  contain 
only  one  such  substance.  2.  That  the  quantity  of  the  active 
substance  present  be  proportioned  to  the  angle  of  rotation. 
3.  That  the  rotation  of  the  red  ray  be  known  for  one  given 
degree  of  concentration. 

Now,  in  determining  the  quantity  of  crystallisable  sugar 
in  the  syrups  obtained  from  plants,  in  molasses,  &c.,  a  diffi- 
culty arises  from  the  presence  of  other  kinds  of  sugar,  viz., 
glucose,  and,  more  especially,  the  uncrystallisable  sugar  of 
fruits,  which  rotates  to  the  left.  This  difficulty  may,  in  most 
cases,  be  obviated  by  boiling  the  liquid  with  hydrochloric 
acid,  whereby  the  crystallisable  sugar  (cane-sugar)  is  con- 
verted into  the  las vo- rotatory  sugar  of  fruits,  while  the  other 
kinds  of  sugar  remain  unaltered.  The  rotatory  power  of 
cane-sugar  is  not  sensibly  affected  by  heat ;  but  that  of  un- 
crystallisable sugar  decreases  considerably  as  the  tempera- 
ture rises.  Thus,  when  cane-sugar  is  heated  with  hydrochloric 
acid  to  68°  C,  the  resulting  fruit-sugar  exhibits  at  different 
temperatures  the  following  rotatory  powers  : — 

Temperature      10°        15°        20°        25°        30°        35° 

Rotatory  power  (that  of  cane- 1    g 

sugar)=100° J"^^  "^^  "^^  ^^^       2^  2^^ 

Suppose,  now,  a  solution  of  cane-sugar  containing  164*71 
grammes  in  a  litre,  which,  in  a  column  20  centimeters  long, 

L  L  3 


474  CIRCULAR  POLARISATION. 

deflects  the  red   ray  15*3°  to  the   right,   to   be  heated  to 

68°  C,  with  -^  of  its  volume  of  hydrochloric  acid,  and  the 

liquid,  after   cooling  to  15°  C,  to  be  introduced  into  the 

polarising  apparatus  in  a  tube  22  centimeters  long,  which 

will  contain  the  same  number  of  atoms  of  sugar  as  a  tube 

20   centimeters   long   of  the   liquid  before   the  addition   of 

the  acid.      The  red  ray  will  then  be  deflected  to  the  left 

by  0-36  X  15-3°  =  d'S''.     Consequently,  the  diff*erence  in  the 

positions  of  the  eye-piece   before   and  after  the  conversion 

will  amount  to  15-3°  +  d-d""  =  20-8°. 

If,  then,  any  mixed  solution  of  cane-sugar  and  uncrys- 

tallisable  fruit-sugar,  containing  164*71  grammes  of  sugar  in  a 

litre,  be  treated  as  above,  and  the  difference  in  the  positions 

in  the  eye-piece  before  and  after  the  conversion  be  5*2°,  tho 

temperature  being  15°  C,  the  amount  of  crystallisable  sugar 

5*2 
in  the  mixture  is .  164*71  =  41*2  grammes.* 

20-8 

If  the  mixture  contains  grape  or  starch-sugar  mixed  with 
cane-sugar,  it  must  be  heated  to  80°  C.  before  being  intro- 
duced into  the  saccharimeter,  because  the  rotatory  power  of 
grape  or  starch-sugar  decreases  considerably  after  a  while 

•  Let  n  be  the  observed  deviation  before  inversion,  n'  the  dcxtro- rotation 
produced  by  the  crystallisable  sugar,  n"  the  laivo-rotation  produced  by  tho 
uncrystallisable  fruit-sugar.  Also,  let  n,  be  the  observed  deviation  in  a  column 
of  liquid  of  the  same  length,  after  the  liquid  has  been  heated  with  -^^  of  its 
volume  of  hydrochloric  acid  ;  and  suppose  that  a  quantity  of  cane-sugar  which 
produces  a  deviation  of  n'  to  the  right,  yields,  when  thus  treated,  a  quantity 
of  uncrystallisable  sugar,  which  produces  a  deviation  of  Kn'  to  the  left  (at 
15°C.,  JT  =  0-36).  Then,  for  the  determination  of  n'  and  n",  we  have  the  two 
equations  : — 

n    =n'  -  n" 

A  mixture  of  cane-sugar  with  starch-sugar  or  grape-sugar  may  be  treated 
in  exactly  the  same  manner,  since  only  the  cane-sugar  has  its  direction  of 
rotation  reversed  ;  and  in  this  case,  n'  and  n"  will  be  determined  by  the 
equations  : — 

n     =  n'  +  n" 

'-in,=n"-Kn! 


CIRCULAR  POLARISATION. 


475 


at  ordinary  temperatures,  but  quickly  attains  its  minimum 
value  when  the  liquid  is  heated  to  80°. 

If  grape  or  starch  sugar  is  present  together  with  uncrys- 
tallisable  fruit-sugar,  the  problem  is  indeterminate,  because 
neither  of  these  sugars  has  its  rotating  action  reversed  by 
treatment  with  acids. 

The  following  table  contains  a  few  of  the  results  obtained 
by  the  method  just  described.  If  the  liquid  to  be  examined 
contains  nothing  but  crystallisable  sugar,  we  have  merely  to 
look  in  the  last  column  but  one  for  the  number  of  degrees 
read  off  on  the  compensator ;  and  the  corresponding  number 
in  the  last  column  gives  the  number  of  grammes  of  sugar 
in  a  litre  of  the  liquid.  If  other  optically  active  substances 
are  present,  and  inversion  is  consequently  necessary,  the 
results  are  found  by  means  of  the  readings  in  the  first  six 
columns. 

Table  for  the  Analysis  op  Sacchakine  Solutions.* 


Sum  or  difference  of  the  readings  before  and  after  the  inversion  of 
the  sugar,  the  last  reading  being  made  at  the  temperature  of 

Degrees. 

Grammes 
of  sugar 
in  a  litre. 

lOO 

150 

20° 

250 

30O 

35° 

1-4 

1-4 

1-3 

1-3 

1-3 

1-3 

1 

1-64 

13-9 

13-6 

13-4 

13-1 

12-9 

12-6 

10 

16-47 

27-8 

27-3 

26-8 

26-3 

25-8 

25-3 

20 

32-94 

41-7 

40-9 

40-2 

39-4 

38-7 

37-9 

30 

49-41 

55-6 

54-6 

53-6 

52-6 

51-6 

50-6 

40 

65-88 

69-5 

68-2 

67-0 

65-7 

64-5 

63-2 

50 

82-35 

83-4 

81-9 

80-4 

78-9 

77-4 

75-9 

60 

98-82 

97-3 

95-5 

93-8 

92-0 

90-3 

88-5 

70 

115-29 

111-2 

109-2 

107-2 

105-2 

103-2 

1012 

80 

131-76 

125-1 

122-8 

120-6 

118-3 

116-1 

113-9 

90 

148-23 

139-0 

136-5 

134-0 

131-5 

1290 

126-5 

100 

164-71 

152-9 

150-1 

147-4 

144-6 

141-9 

139-1 

110 

181-18 

166-8 

163-8 

160-8 

157-8 

154-8 

151-8 

120 

197-65 

180-7 

177-4 

174-2 

170-9 

167-7 

164-4 

130 

214-21 

♦  This  table  is  extracted  from  the  much  more  extensive  one  given  in  the 
"  Traitc  de  Chimie  Goneralo "  par  Pelouzo  ct  Fremy.  Paris,  1855,  t  It. 
pp.  620—622. 

L  L  4 


476 


CIRCULAR  POLARISATION. 


Relations  between  Rotatory  Power  and  Crystalline  Form, — 
It  has  already  been  observed  that  silica  and  a  few  other 
inorganic  bodies  exhibit  circular  polarisation,  only  when 
crystallised.  Moreover,  crystals  of  the  same  substance  — 
quartz,  for  example — which  exert  opposite  actions  on  polarised 
light,  often  exhibit  a  remarkable  opposition  in  their  crys- 
talline forms.  Thus,  the  ordinary  form  of  quartz,  the  six- 
sided  prism  with  pjTamidal  six-sided  summits,  is  sometimes 
found  modified  in  the  manner  shown  in  figs.  34,  35,  the  solid 
angles  formed  by  the  meeting  of  two  pyramidal  with  two 

Fig.  34.  Fig.  35. 


prismatic  faces,  being  truncated  with  faces,  a,  obliquely 
inclined  to  the  faces  of  the  prism ;  these  truncation  faces, 
however,  are  only  six  in  number,  whereas  to  form  a  complete 
holohedral  combination  (since  these  faces  are  unequally 
inclined  to  those  of  the  prism),  there  should  be  twenty-four 
of  them,  two  at  each  of  the  twelve  angles  above-mentioned  : 
the   form   is   therefore  tetartohedral.*      But,  further,  these 

*  Hdohedral  forms  are  those  which  are  bounded  by  similar  faces  occurring 
in  the  greatest  possible  number  consistent  with  the  law  of  symmetry  which  de- 
termines their  position  ;  if  the  number  of  such  faces  is  only  one-half  of  what  it 
might  be,  the  form  is  hemihedral ;  if  only  one-fourth,  it  is  tetartohedral.  The 
regular  octohedron  is  a  holohedral  crystal,  and  tlie  tetrahedron  is  the  hemi- 
hedral form  coiTcsponding  to  it ;  similarly,  the  rhombohedron  is  the  hemihedral 
form  of  the  double  six-sided  pyramid.  Hemihedral  and  tetartohedral  forms 
often  occur  associated  with  holohedral  fonus  in  the  same  crystal. 


CIRCULAR  POLARISATION.  477 

tetartohedral  faces  are  not  always  placed  alike,  occurring  in 
some  crystals  on  the  right  of  a  prismatic  face  above,  and  on 
the  left  below,  and  the  contrary  in  others,  as  shown  in  the 
above  figures.  The  two  forms  of  crystal  thus  produced, 
though  their  faces  are  alike  in  number  and  in  form,  are 
evidently  not  superposible,  but  the  one  may  be  regarded  as 
the  reflected  image  of  the  other.  Now,  the  crystals  of  the 
one  kind  invariably  exhibit  dextro-rotatory,  and  those  of  the 
other  kind  Isevo-rotatory,  power.  The  same  kind  of  opposite 
tetartohedry,  and  accompanied  by  a  corresponding  opposition 
of  rotatory  power,  is  found  in  the  few  other  inorganic  com- 
pounds (p.  468)  which  exhibit  circular  polarisation. 

This  remarkable  relation  between  rotatory  power  and 
crystalline  form  is,  however,  much  more  strikingly  exhibited 
by  certain  organic  compounds. 

Tartaric  acid  and  its  salts  turn  the  plane  of  polarisation  to 
the  right ;  racemic  acid,  which  is  identical  in  chemical  com- 
position with  tartaric  acid,  and  agrees  with  it  in  nearly  all  its 
chemical  relations,  has  no  action  whatever  on  polarised  light, 
either  in  the  free  state  of  the  acid  or  when  combined  with 
bases.  Now,  the  crystals  of  tartaric  acid  and  the  tartrates  are 
hemihedral,  those  of  racemic  acid  and  the  racemates,  with  one 
exception,  are  holohedral  The  exception  alluded  to  is  the 
racemate  of  soda  and  ammonia.  A  solution  of  racemate  of 
soda  and  racemate  of  ammonia,  in  equivalent  proportions, 
yields  by  evaporation  crystals  of  a  double  salt,  the  form  of 
which  is  represented  in  figs.  36,  37. 

It  is  a  right  rectangular  prism  P,  M,  T,  having  its  lateral 
edges  replaced  by  the  faces  b^,  and  the  intersection  of  these 
latter  faces,  with  the  face  T,  replaced  by  a  face  A.  If  the 
crystal  were  holohedral,  there  would  be  eight  of  these  faces, 
four  above,  and  four  below  ;  but,  as  the  figures  show,  there 
are  but  four  of  them,  placed  alternately:  moreover,  these 
hemihedral  faces  occupy  in  different  crystals,  not  similar, 
but  opposite  positions ;  so  that,  as  in  the  case  of  quartz,  the 


478 


CIRCULAR   POLARISATION. 


one  kind  of  crystal  is,  as  it  were,  the  reflected  image  of  the 
other. 

Fig.  36.  Fig.  37. 


But  further ;  by  carefully  picking  out  the  two  kinds  of 
crystals,  and  dissolving  them  separately  in  water,  solutions 
are  obtained,  which,  at  the  same  degree  of  concentration, 
exert  equal  and  opposite  actions  upon  polarised  light,  the 
one  deflecting  the  plane  of  polarisation  to  the  right,  the 
other,  by  an  equal  amount,  to  the  left.  Moreover,  the  solu- 
tions of  the  right  and  left-handed  crystals,  yield,  by  evapora- 
tion, crystals,  each  of  its  own  kind  only ;  and  by  mixing  tho 
solutions  of  these  crystals  with  chloride  of  calcium,  lime-salts 
are  obtained,  which,  when  decomposed  by  sulphuric  acid, 
yield  acids,  agreeing  with  each  other  in  composition,  and 
in  every  other  respect,  except  that  their  crystalline  forms 
exhibit  opposite  hemihedral  modifications,  and  their  solutions, 
when  reduced  to  the  same  degree  of  concentration,  exhibit 
equal  and  opposite  effects  on  polarised  light. 

Of  the  two  acids  thus  obtained,  the  one  which  turns  the 
plane  of  polarisation  to  the  right  is  identical  in  every  respect 
with  ordinary  tartaric  acid.  The  other  may  be  called,  for 
distinction,  antitartaric  acid.  When  equal  weights  of  these 
two  acids  are  dissolved  in  water,  and  the  solutions  mixed,  a 
liquid  is  obtained,  which  has  no  action  whatever  on  polarised 
light,  and  yields  by  evaporation,  holohedral  crystals  of  racemic 
acid,  A  similar  result  is  obtained  by  mixing  equal  quantities 
of  any  of  the  salts  of  the  two  acids,  excepting  the  double 
salt  of  soda  and  ammonia. 


CIRCULAR  POLARISATION.  470 

Hence  it  appears  that  racemic  acid,  a  body  which  has  no 
action  upon  polarised  light,  and  crystallises  in  holohedral 
forms,  is  a  compound  of  two  acids  (tartaric  and  antitar- 
taric*),  which  have  equal  and  opposite  effects  on  polarised 
light,  and  crystallise  in  similar  but  opposite  hemihedral 
forms.  There  is  also  another  property  in  which  these  acids 
differ,  viz.  in  their  pyro-electric  relations.  The  crystals  of 
both  these  acids  become  electric  when  heated,  but  the  corre- 
sponding extremities  of  the  two  exhibit  opposite  electrical 
states.     Racemic  acid  is  not  pyro-electric. 

Tartaric  acid  may  be  converted  into  racemic  acid  by  the 
action  of  heat,  provided  only  it  be  associated  with  some  sub- 
stance which  will  enable  it  to  bear  a  somewhat  high  tempe- 
rature without  decomposing.  There  are  many  substances 
whose  effect  on  polarised  light  is  altered  by  heat.  This  is 
remarkably  the  case  with  the  alkaloids  of  the  cinchona  bark. 
When  cinchonine,  or  any  of  its  salts  (which  rotate  to  the  right), 
is  heated  in  such  a  manner  as  not  to  produce  decomposition, 
it  is  transformed  into  an  isomeric  alkaloid,  cinchonicine, 
which  turns  the  plane  of  polarisation  to  the  left.  Similarly, 
quinine,  which  rotates  the  plane  of  polarisation  to  the  left, 
is  converted  by  heat  into  quinicine,  which  turns  it  to  the 
right.  Now,  when  tartrate  of  cinchonine  is  heated,  it  is 
first  converted  into  tartrate  of  cinchonicine,  and  if  the  heat  be 
then  continued,  the  change  extends  to  the  tartaric  acid,  half 
of  which  is  converted  into  antitartaric  acid.  If  the  process 
be  stopped  at  a  certain  point,  and  the  fused  mass  treated  with 
water,  a  solution  is  obtained  which  yields,  first,  crystals  of 
antitartrate,  and  afterwards,  of  tartrate  of  cinchonicine. 
But  if  the  heat  be  longer  continued,  the  two  acids  unite,  and 
form  racemate  of  cinchonicine,  from  which  racemic  acid  may 
be  prepared,  identical  in  every  respect  with  ordinary  race- 
mic acid,  and  separable  by  the  same  means  into  the  two 
opposite  tartaric  acids. 

*  Thence  also  called  respectively  dextro-racemie  and  lavo-raceniic  acids. 


480  CIRCULAR    rOLARlSATION. 

But,  what  is  very  remarkable,  there  is  formed  at  the  same 
time  a  modification  of  tartaric  acid,  which  has  no  action 
whatever  on  polarised  light,  and  yet  is  not  separable  into  the 
two  opposite  acids.  In  fact,  when  the  fused  mass  obtained 
by  heating  tartrate  of  cinchonine  is  treated  with  water,  and 
chloride  of  calcium  added,  a  precipitate  is  formed,  consisting 
of  racemate  of  lime,  and  the  filtrate,  if  left  at  rest,  deposits 
crystals  of  the  lime-salt  of  inactive  tartaric  acid. 

There  are  other  organic  compounds  which  are  also  opti- 
cally active  in  their  ordinary  forms,  but  exhibit  inactive  and 
inseparable  modifications.  Malic  acid,  as  it  exists  in  fruits, 
turns  the  plane  of  polarisation  to  the  right ;  so  likewise  does 
aspartic  acid  obtained  by  the  action  of  acids  and  alkalies  on 
asparagin.  Now  both  these  acids  may  be  formed  from  fu- 
maric  acid,  an  optically  inactive  substance.  Acid  fumarate 
of  ammonia  is  C8H3(NH4)08=C8H7N08,  which  is  also  the 
formula  of  aspartic  acid,  and  this  acid  is  actually  formed  by 
heating  the  acid  fumarate  of  ammonia.  But  the  aspartic 
acid  thus  produced  is,  like  fumaric  acid,  optically  inactive. 
Again,  aspartic  acid  is  converted  into  malic  acid  by  the 
action  of  nitrous  acid  : — 

CgH^NOg  +  NO3  =  CgHgOjo  +  2N  +  IIO. 

Aspartic  acid.  Malic  acid. 

Both  active  and  inactive  aspartic  acids  undergo  this  trans- 
formation ;  but  active  aspartic  acid  yields  active  malic  acid, 
and  inactive  aspartic  acid  yields  inactive  malic  acid.  Neither 
inactive  aspartic  nor  inactive  malic  acid  can  be  separated  into 
two  acids  oppositely  active. 

Common  oil  of  turpentine  possesses  considerable  dextro- 
rotatory power;  but  the  isomeric  substance  obtained  by 
heating  the  artificial  solid  camphor  of  turpentine  with  quick- 
lime is  optically  inactive. 

Fusel  oil  has  lately  been  shown  by  Pasteur  to  be  a  mix- 
ture of  two  kinds  of  amylic  alcohol,  which  differ  slightly  in 


FLUORESCENCE.  481 

boiling  point.     One  of  these  alcohols  is  optically  active,  the 
other  inactive. 

Rotatory  Power  induced  by  Magnetic  Action. —  Faraday  lias 
made  the  remarkable  discovery,  that  bodies  which,  in  their 
ordinary  state,  exert  no  particular  action  on  polarised  light, 
acquire  the  circular-polarising  structure  when  subjected  to 
the  action  of  powerful  electric  or  magnetic  forces.  A  polar- 
ised ray  passing  along  the  axis  of  a  prism  or  cylinder  of  any 
transparent  substance,  such  as  water  or  glass,  has  its  plane 
of  polarisation  deflected  to  the  right  or  left,  as  soon  as  the 
medium  is  subjected  to  the  action  of  an  electric  current 
passing  round  it  at  right  angles  to  the  axis,  or  to  that  of  two 
powerful  opposite  magnetic  poles,  so  placed  that  their  line  of 
junction  shall  be  parallel  to  the  axis  of  the  column  of  the 
transparent  substance.  The  rotation  ceases  as  soon  as  the 
electric  or  magnetic  force  ceases  to  act ;  its  amount  varies 
directly  as  the  strength  of  the  current;  and  its  direction 
changes  with  that  of  the  current  or  of  the  magnetic  force. 
If  the  medium  has  a  rotatory  power  of  its  own,  the  total 
effect  is  equal  to  the  sum  or  difference  of  the  natural  and 
induced  rotations,  according  as  the  electric  or  magnetic  force 
acts  with  or  against  the  natural  rotatory  power  of  the  medium. 


CHANGE  OF  REFRANGIBILITY  OF  LIGHT.  —  FLUORESCENCE. 

It  was  observed  some  years  ago  by  Sir  John  Herschel,  that 
a  solution  of  sulphate  of  quinine,  though  perfectly  colourless 
by  transmitted  light,  exhibits  in  certain  aspects  a  peculiar  blue 
colour.  This  blue  light  was  found  to  be  produced  only  by 
a  very  thin  stratum  of  the  liquid  adjacent  to  the  surface  by 
which  the  light  entered ;  and  the  incident  beam,  after  having 
passed  through  the  stratum  from  which  the  blue  light  came, 
was  not  sensibly  weakened  or  coloured,  but  had  lost  the  power 
of  producing  the  usual  blue  colour  when  admitted  into  another 


482  FLUOKESCENCE. 

solution  of  sulphate  of  quinine.     Light  thus  modified  was 
said  by  Sir  J.  Herschel  to  be  epipolised. 

Similar  phenomena  were  observed  by  Sir  D.  Brewster  in 
an  alcoholic  solution  of  chlorophyll,  the  green  colouring 
matter  of  leaves,  the  path  of  a  beam  of  sunlight  admitted  into 
the  green  solution  being  marked  by  a  bright  light  of  a  blood- 
red  colour.  The  same  appearance  was  afterwards  observed 
in  various  vegetable  solutions  and  essential  oils,  and  in  some 
solids.  Brewster  distinguished  this  phenomenon  by  the  name 
of  internal  dispersion,  attributing  it  to  the  irregular  reflection 
of  the  light  from  coloured  particles  suspended  in  the  liquid, 
and  was  of  opinion  that  Herschel's  epipolic  dispersion  was  only 
a  particular  case  of  this  internal  dispersion. 

The  true  explanation  of  these  remarkable  phenomena  has, 
however,  been  given  by  Professor  Stokes*,  who  has  submitted 
the  whole  subject  to  the  most  searching  investigation,  and 
shown  that  the  peculiar  dispersion  produced  by  sulphate  of 
quinine,  and  the  other  liquids  above  mentioned,  is  due  to  a 
change  of  refrangihility  in  the  rays  of  light.  The  following 
experiment  renders  this  evident : — 

A  solar  spectrum  is  formed  by  means  of  an  achromatic  lens, 
and  one  or  more  prisms  of  flint  glass,  sufficiently  pure  to 
render  visible  the  principal  fixed  lines,  and  a  tube  filled  with 
a  solution  of  sulphate  of  quinine  is  passed  along  this  spectrum, 
from  the  red  towards  the  violet  end.  Nothing  peculiar  is 
observed  while  the  tube  is  held  in  the  less  refrangible  part  of 
the  spectrum,  the  light  passing  through  it  freely  and  without 
sensible  modification  ;  but  just  before  it  reaches  the  extremity 
of  the  violet,  a  peculiar  blue  diffused  light  makes  its  appear- 
ance at  the  surface  of  the  fluid  by  which  the  light  enters,  and 
remains  visible  even  after  the  tube  has  passed  beyond  the 
violet  into  the  invisible  portion  of  the  spectrum,  acquiring  in 
fact  its  greatest  intensity  at  a  certain  distance  beyond  the  ex- 
treme violet. 

*  Phil.  Trans.  1852.  ii.  463. 


FLUORESCENCE.  48S 

The  stratum  of  liquid  from  which  the  diffused  blue  light 
emanates  is  thinner  in  proportion  as  the  incident  rajs  are 
more  refrangible ;  and,  from  a  little  beyond  the  extreme  violet 
to  the  end  of  the  spectrum,  the  blue  space  is  reduced  to  an 
excessively  thin  stratum  adjacent  to  the  surface  by  which  the 
rays  enter.  It  appears,  therefore,  that  the  solution,  though 
transparent  with  respect  to  nearly  the  whole  of  the  visible  rays, 
is  of  an  inky  blackness  with  respect  to  the  invisible  rays  more 
refrangible  than  the  violet.  Nevertheless,  these  rays,  when 
once  they  have  been  converted  into  the  visible  blue  light, 
pass  through  the  liquid  with  facility.  They  must,  therefore,  be 
essentially  altered  in  character.  Now  a  change  in  the  quality 
of  light  must  consist,  either  in  a  modification  of  its  state  of 
polarisation,  or  in  its  period  of  undulation.  The  former  sup- 
position is  excluded  by  the  fact  that  the  light  thus  modified  is 
not  polarised  at  all.  It  must,  therefore,  have  undergone  a 
change  in  its  rate  of  vibration,  and  consequently  a  change  of 
refrangibility.  The  existence  of  this  change  is,  moreover, 
distinctly  proved  by  examining  the  diffused  light  with  a  prism. 
It  is  then  found  to  be  by  no  means  homogeneous,  but  to  be 
resolvable  into  rays  of  unequal  refrangibility,  the  whole  of 
which  are  however  comprised  within  the  limits  of  the  visible 
spectrum.  The  diffused  blue  light  consists  of  the  chemical  rays 
rendered  visible  by  a  change  in  their  refrangibility. 

The  diffusion  thus  produced  is  entirely  distinct  from  that 
which  is  due  to  reflection  from  irregularities  or  suspended 
particles.  The  two  phenomena  are  often  produced  together 
in  the  same  medium ;  but  they  are  easily  distinguished  by  the 
fact  that  the  light  diffused  by  irregular  reflection  is  more  or 
less  polarised,  whereas  the  light  diffused  in  the  manner  above 
described  is  entirely  unpolarised,  even  if  the  incident  rays 
were  themselves  polarised.  This  phenomenon,  to  which  Pro- 
fessor Stokes  originally  gave  the  name  of  true  diffusion,  to 
distinguish  it  from  the  false  diffusion  produced  by  irregular 
reflection,  is  now  called  Fluorescence. 


484  FLUORESCENCE. 

It  is  exhibited  by  many  solutions,  and  by  many  solid  bodies, 
opaque  as  well  as  transparent,  the  colour  of  the  diffused  light 
varying  with  the  nature  of  the  medium.  An  aqueous  infusion 
of  horse-chestnut  bark  exhibits  it  very  strongly,  producing  the 
same  blue  colour  as  sulphate  of  quinine.  Many  compounds  of 
sesquioxide  of  uranium  are  also  highly  fluorescent,  and  diffuse 
a  greenish-blue  light,  especially  the  nitrate,  and  canary-glass 
(ii.  256).  A  decoction  of  madder  mixed  with  alum  gives  a 
yellow  or  orange-yellow  fluorescence ;  tincture  of  turmeric 
and  alcoholic  extract  of  thorn-apple  seeds  diffuse  a  greenish 
light ;  an  alcoholic  solution  of  chlorophyll,  a  red  light. 

When  the  fluorescence  is  strong,  as  with  sulphate  of  qui- 
nine, it  may  be  seen  by  merely  viewing  the  substance  by 
ordinary  diffused  daylight.  For  more  accurate  observation, 
and  for  detecting  fluorescence  when  it  exists  only  in  a  slight 
degree,  the  following  method  is  recommended  by  Professor 
Stokes*:  — 

Light  is  admitted  into  a  darkened  room  through  a  hole 
several  inches  in  diameter  in  the  window  shutter,  and  the 
object  to  be  examined  is  placed  on  a  small  shelf,  blackened  at 
the  top,  and  fixed  just  below.  The  hole  is  covered  with  an 
absorbing  medium,  called  the  pHncipal  absorbent,  so  selected 
as  to  transmit  only  the  feebly  luminous  and  invisible  rays  of 
high  refrangibility.  The  body  on  the  shelf  is  viewed  through 
the  second  medium,  the  complementary  absorbent,  which  is 
chosen  so  as  to  be  as  transparent  as  possible  to  those  rays  which 
are  absorbed  by  the  first,  and  to  absorb  all  the  rays  which 
are  transmitted  by  the  first.  If  the  media  are  well  selected, 
they  produce  a  very  near  approach  to  perfect  darkness  ;  and 
if  the  object  appears  unduly  luminous,  that  effect  most  pro- 
bably arises  from  fluorescence.  To  determine  whether  the 
illumination  is  really  due  to  that  cause,  the  complementary 
absorbent  is  removed  from  before  the  eyes  to  the  front  of  the 
aperture,  when  the  illumination,  if  really  due  to  fluorescence, 

*  Phil.  Mag.  [4],  vi.  304, 


FLUORESCENCE.  485 

almost  wholly  disappears ;  whereas,  if  it  be  due  merely  to 
scattered  light  capable  of  passing  through  both  media,  it 
remains.  In  examining  feebly  fluorescent  substances,  how- 
ever, it  is  better  to  keep  the  second  medium  in  its  place  before 
the  eye,  and  to  us©  a  third  medium,  the  transfer-medium, 
placing  the  last  alternately  in  the  path  of  the  incident  rays, 
and  between  the  object  and  the  eye.  Still  greater  delicacy  of 
observation  is  attained  by  placing  the  substance  side  by  side 
with  a  small  white  porcelain  tablet,  which  is  quite  destitute 
of  fluorescence,  and  examining  the  two  as  above.  Or,  again, 
the  object  being  placed  on  the  tablet,  a  slit  is  held  close  to  it, 
in  such  a  position  as  to  be  seen  projected,  partly  on  the  object, 
partly  on  the  tablet,  and  the  slit  is  viewed  through  a  prism. 
The  fluorescence  of  the  object  is  evidenced  by  light  appearing 
in  regions  of  the  spectrum,  in  which  the  rays  coming  through 
the  principal  absorbent,  and  scattered  by  the  tablet,  produce 
nothing  but  darkness.  These  methods  are  delicate  enough 
to  show  the  fluorescence  of  white  paper,  even  on  a  very 
gloomy  day. 

It  is  not  merely  the  most  refrangible  rays  that  are  capable 
of  producing  fluorescence ;  the  rays  of  any  part  of  the  spec- 
trum may  undergo  this  change.  By  examining  different 
media  with  the  spectrum  in  the  manner  already  described,  it 
is  seen  that  the  fluorescence  begins,  sometimes  in  the  blue, 
sometimes  in  the  yellow.  With  an  alcoholic  solution  of 
chlorophyll,  it  begins  in  the  red.  But  wherever  the  change 
of  refrangibility  may  begin,  it  is  always  in  one  direction,  con- 
sisting in  a  diminution  of  the  index  of  refraction,  and  a  con- 
sequent depression  of  the  light  in  the  scale  of  colours.  In 
other  words,  the  length  of  the  wave  w  increased,  and  its  velocity 
of  undulation  diminished.  The  vibrations  of  the  ether  in  the 
incident  ray  appear  to  excite  disturbances  within  the  complex 
molecules  of  the  fluorescent  medium,  whereby  new  vibrations 
are  excited  in  the  ether,  differing  in  period  from  those  of  the 
incident  ray.     The  portion  of  the  light  which  has  produced 

VOL.  IL  M  M 


486  FLUORESCENCE. 

this  molecular  disturbance  is  used  up,  or  absorbed,  and 
thereby  lost  to  visual  perception,  just  as  heat  is  converted 
into  mechanical  work.  It  is  probable  that  the  absorption  of 
light  always  takes  place  in  this  manner.  The  well-known 
fact  of  the  conversion  of  luminous  rays  into  invisible  calorific 
rays,  is  a  striking  instance  of  diminution  of  refrangibility 
accompanied  by  absorption. 

As  the  most  refrangible  rays  are  the  most  active  in  pro- 
ducing fluorescence,  it  is  natural  that  this  effect  should  be 
most  strikingly  exhibited  by  the  light  of  flames  which  are 
rich  in  those  rays,  —  the  flame  of  alcohol  and  of  sulphur,  for 
example.  These  flames  do,  in  fact,  produce  the  effect  in  a 
higher  degree  even  than  sunlight.  An  extremely  beautiful 
effect  is  produced  by  exposing  a  number  of  highly  fluorescent 
media,  such  as  sulphate  of  quinine,  infusion  of  horse-chestnut 
bark,  and  canary-glass,  to  the  flame  of  sulphur  burning  in 
oxygen  in  a  dark  room. 

The  similarity  of  the  blue  light  diffused  by  most  fluorescent 
media  to  the  phosphorescence  exhibited  by  certain  bodies,  might 
lead  us  to  suppose  that  the  two  phenomena  proceed  from  the 
same  cause.  Such,  however,  is  not  the  case:  for  fluorescence 
is  entirely  dependent  on  the  incidence  of  certain  rays,  whereas 
phosphorescence  is  not ;  and,  moreover,  there  is  no  apparent 
connection  between  fluorescent  and  phosphorescent  bodies. 
So  far  as  observation  has  yet  gone,  phosphorescent  bodies  are 
not  fluorescent. 


SPECTRA   EXHIBITED   BY   COLOURED   MEDIA. 

The  colour  of  an  object  depends  upon  the  rays  which  it 
reflects  or  transmits  to  the  eye ;  it  is,  in  fact,  the  mixture  or 
resultant  of  all  the  rays  which  the  body  does  not  absorb. 
We  cannot,  however,  from  observation  with  the  unassisted 
eye,  judge  with  certainty  of  the  rays  which  are  transmitted 
or  reflected ;  because  the  same,  or  nearly  the  same,  com- 


SPECTRA   PRODUCED   BY   COLOURED   MEDIA.  487 

pound  tint  may  result  from  the  union  of  very  different  pri- 
mary colours.  Thus  a  body  may  exhibit  an  indigo  or  violet 
tint,  either  because  it  absorbs  all  the  rays  excepting  those 
which  form  the  indigo  or  violet  portions  of  the  spectrum,  or 
because  it  reflects  or  transmits  the  red  and  blue  rays  in  cer- 
tain proportions ;  similarly,  a  green  colour  may  be  the  pure 
green  of  the  spectrum,  or  a  mixture  of  yellow  and  blue.  In 
such  cases,  examination  with  the  prism  will  show  of  what 
primary  rays  the  colour  is  composed,  and  may  thus  afford  the 
means  of  distinguishing  between  substances  which,  to  ordinary 
observation,  appear  of  the  same  colour. 

Dr.  Gladstone,  who  has  lately  made  some  very  inte- 
resting observations  on  the  absorption  of  light  by  coloured 
liquids*,  introduces  the  liquid  into  a  wedge-shaped  vessel 
placed  before  a  slit  in  the  window-shutter  of  a  darkened 
room,  so  that  the  line  of  light  may  be  seen  through  various 
thicknesses  of  the  liquid,  from  the  thinnest  possible  fihn 
to  a  stratum  perhaps  three-quarters  of  an  inch  thick, 
and  examines  this  line  of  coloured  light  with  a  prism  held 
with  its  refracting  angle  parallel  to  the  line  of  light.  The 
whitish  portion  of  the  line,  where  the  light  traverses  but 
a  thin  film  of  the  liquid,  is  thereby  expanded  into  a  spectrum 
differing  but  little  from  that  which  is  given  by  unaltered  day- 
light;  but  as  the  line  of  light  is  viewed  through  deeper 
portions  of  the  liquid,  some  rays  are  seen  to  diminish  in 
intensity,  others  gradually  to  die  out,  while  others  almost  im- 
mediately disappear,  giving  place  to  perfect  darkness.  With 
a  good  prism,  on  a  tolerably  clear  day,  the  most  conspicuous 
of  Fraunhofer's  lines  may  be  seen.  The  appearances  pre- 
sented may  be  understood  from  the  following  representations 
of  the  effects  produced  by  solutions  of  sesquichloride  of 
chromium  (Fig.  38)  and  permanganate  of  potash  (Fig.  39).t 


*  Chem.  Soc.  Qu.  J.  x.  79. 

f  For  representations  of  the  spectra  exhibited  by  a  considerab'o  number  of 
^Imiv^H  liniiirla   spft  Dr.  Cilsiflstone's  nsiner  nhnvp.  rp.fp.rrp.d  to. 


]»  M  2 


488 


LIGHT. 


The  right-hand  side  of  these  figures  corresponds  with  the  red 
extremity  of  the  spectrum  :  the  letters  refer  to  Fraunhofer's 
lines. 


Fig.  38. 


Fig.  39. 


G^      F        Ji  B 


A  comparison  of  the  spectra  exhibited  by  different  salts, 
only  one  constituent  of  which  is  coloured,  shows  that,  with 
very  few  exceptions,  all  the  compounds  of  the  same  base  or 
acid  have  the  same  effect  on  the  rays  of  light.  This  law  is 
seen  to  hold  good  in  many  instances  which  at  first  sight 
appear  exceptional.  Thus  it  is  well  known  that  some  salts  of 
chromic  oxide  are  green,  others  red  or  purple.  Now  these 
differently-coloured  chromic  salts  all  exhibit  the  same  general 
form  of  spectrum  (Fig.  38),  in  which  the  violet  and  indigo 
rays  are  very  soon  cut  off;  and  as  the  thickness  increases,  the 
light  is  more  and  more  concentrated  about  two  points,  one  in 
the  red,  the  other  in  the  bluish  green,  the  red  ray  penetrating 
with  the  greatest  facility.  Hence  it  is  that  the  chloride  and 
other  salts  of  chromium,  which  are  green  in  moderately 
dilute  solutions,  appear  purple  or  red  when  we  look  through 
a  strong  or  very  deep  solution.  The  acetate  absorbs  the 
green  rays  more  readily,  and  therefore  appears  green  only  in 
very  weak  solutions,  or  in  thin  strata,  while  the  "  red  potassio- 
oxalate"  absorbs  the  green  so  speedily  that  the  thinnest 
portion  of  it  appears  bluish  red. 


SPECTRA   PRODUCED  BY  COLOURED   MEDIA.  489 

Salts  composed  of  a  coloured  base  and  a  coloured  acid 
exhibit  colours  compounded  of  the  rays  which  are  not  absorbed 
by  either,  the  resultant  colour  bearing,  in  many  instances,  but 
little  resemblance  to  the  original  colours.  Thus,  the  acid  chro- 
mate  of  chromic  oxide,  a  compound  of  two  substances  which 
give  respectively  yellow  and  green  solutions,  is  not  bright 
green,  but  brownish-red,  because  the  chromic  acid  cuts  off 
nearly  all  the  blue  and  violet  rays,  while  the  oxide  of 
chromium  absorbs  the  yellow  and  the  greater  part  of  the 
green. 

Some  salts,  which  are  but  slightly  coloured,  nevertheless 
exhibit  very  characteristic  spectra.  Thus,  a  solution  of  sul- 
phate of  didyraium,  which  has  but  a  faint  rose  colour,  exhibits, 
when  examined  by  the  hollow  wedge  and  prism,  a  spectrum 
containing  two  very  black  lines,  one  in  the  yellow,  the  other 
in  the  green.  These  lines  are  visible  in  very  weak  solutions 
of  didymium,  and  therefore  serve  as  a  delicate  test  for  that 
metal ;  they  moreover  afford  the  means  of  distinguishing  it 
from  cerium  and  lanthanum,  in  the  spectra  of  which  they 
do  not  occur. 


MEASUREMENT   OF   THE   CHEMICAL   ACTION   OF    LIGHT. 

Chlorine  and  hydrogen  combine  under  the  influence  of  light, 
and  form  hydrochloric  acid.  Moreover,  if  the  gaseous  mix- 
ture is  in  contact  with  water,  the  resulting  hydrochloric  acid 
is  immediately  absorbed,  and  the  diminution  of  volume  thus 
produced  affords  a  measure  of  the  amount  of  chemical  action. 
This  mode  of  measurement  was  first  adopted  by  Dr.  Draper, 
of  New  York,  whose  experiments  led  to  the  important  con- 
clusion that  the  chemical  action  of  light  varies  in  direct  propor- 
tion to  the  intensity  of  the  light,  and  to  the  time  of  exposure. 

But  to  give  to  this  method  all  the  exactness  of  which  it  is 
susceptible,  certain  conditions  require  to  be  fulfilled;  the 
chief  of  which  are  perfect  uniformity  in  the  gaseous  mixture, 

M  M   3 


490  MEASUREMENT    OF    TUB 

constancy  of  pressure  on  the  gas  and  liquids  througliout  the 
apparatus,  and  elimination  of  the  disturbing  action  of  radiant 
heat.  These  and  other  essential  conditions  are  completely 
fulfilled  in  the  apparatus  used  by  Professor  Bunsen  and  Dr. 
H.  Roscoe  in  their  late  elaborate  researches  on  the  chemical 
action  of  light.* 

This  apparatus  is  represented  in  figure  40.  To  furnish 
the  mixture  of  chlorine  and  hydrogen  gases  required,  hydro- 
chloric acid  is  decomposed  in  the  glass  vessel  a,  containing  two 
carbon  poles,  connected  by  platinum  wires  with  the  four- 
celled  Bunsen's  battery,  C.  Between  the  battery  and  this 
vessel  is  interposed  an  instrument  called  the  gyrotrope,  by 
means  of  which  the  current  may  be  made  to  pass  either 
directly  through  the  acid  vessel  a,  or  previously  through  the 
vessel  d  containing  very  slightly  acidulated  water,  whereby  the 
current  is  greatly  weakened,  and  the  evolution  of  gas  in  the 
vessel  a  reduced  to  a  small  amount.  The  mixture  of  chlorine 
and  hydrogen  passes  from  the  vessel  a  through  the  washing- 
tube  to,  containing  water,  then  forward  through  a  horizontal 
tube  provided  with  a  glass  cock,  h,  into  the  insolation  vessel  i, 
where  the  gases  are  exposed  to  the  action  of  light.  The  lower 
part  of  this  vessel,  containing  water,  is  blackened  to  protect 
it  from  the  action  of  the  light.  From  the  insolation  vessel, 
the  gas  passes  through  the  horizontal  measuring-tube  K,  pro- 
vided with  a  millimeter  scale,  then  through  the  water  in  the 
small  vessel  /,  and  finally  into  a  vessel  filled  with  fragments 
of  charcoal  and  hydrate  of  lime,  to  absorb  the  excess  of 
chlorino 

When  the  gas  is  made  to  stream  through  the  apparatus,  the 
liquids  in  «,  to,  z,  and  /,  become  gradually  saturated  w^ith  gas; 
and  as  the  saturation  goes  on,  the  composition  of  the  gas  varies. 
At  length,  however,  after  the  stream  of  gas  has  been  continued 
for  three  or  four  days,  the  liquids  become  saturated,  and  then 
the  evolved  gas  is  found  to  consist  of  exactly  equal  volumes 

*  Pogg.  Ann.  c.  43,  481  ;  abstr.       Proceedings  of  the  Royal  Society,  viii. 
235,  23G,  516. 


CHEMICAL    ACTION    OP    LIGHT. 


491 


of  chlorine  and  hydrogen.     This  normal  state  having  been 

attained,  the  apparatus  is  ready  for  use,  and  retains  its  constant 

sensibility  for  weeks, 

req  uiring  only  a  short 

saturation  each  day, 

previous  to  the  actual 

observations. 

To  make  an  obser- 
vation, the  stop-cock 
h  is  closed,  and  the 
light  allowed  to  act 
on  the  gas  in  the 
upper  part  of  the 
vessel  z.  Combina- 
tion then  takes  place, 
accompanied  by  di- 
minution of  volume, 
and  the  external  pres- 
sure forces  the  water 
in  I  through  the  tube 
K  towards  i.  The 
position  of  the  end 
of  the  column  in  the 
scale  measures  the 
diminution  of  vo- 
lume. 

The  pressure  on 
the  gas  in  the  in- 
solation vessel  and 
the  measurinfj-tube 
during  the  observa- 
tions, is  necessarily 
uniform  from  the 
construction  of  the  apparatus ;  but  it  is  further  necessary  that 
uniformity  of  pressure  be  ensured  in  all  parts  of  the  apparatus 

M  3f   4 


492  CHEMICAL  ACTION   OF   LIGHT. 

in  the  intervals  between  the  observations  ;  otherwise  the  com- 
position of  the  gaseous  mixture  will  be  altered,  and  the  results 
will  no  longer  be  exact.  To  ensure  this  uniformity  of  pres- 
sure, the  gas,  after  the  stopcock  h  is  closed,  is  made  to  pass 
through  the  bent  tube  m  v  v,  containing  water,  and  thence 
through  the  tube  p,  which  dips  under  the  water  in  the  vessel 
F,  the  pressure  being  regulated  by  raising  or  depressing  this 
tube  through  the  caoutchouc  mouthpiece  t.  From  the  vessel 
F  the  gas  is  conveyed  by  a  flexible  tube  into  the  condensing 
vessel  G,  containing  charcoal  and  hydrate  of  lime.  As  soon 
as  the  stopcock  h  is  closed,  the  gyrotrope  wire  is  turned,  so 
as  to  cause  the  current  to  pass  through  the  vessel  (Z,  and 
thereby  slacken  the  evolution  of  gas.  When  the  stopcock 
h  is  open,  the  gas  will  pass  one  way  or  the  other,  according 
to  the  depth  at  which  the  tube  p  is  immersed  below  the 
water  in  F. 

To  prevent  any  disturbance  from  the  effects  of  radiant  heat, 
the  light  from  a  coal  gas  flame,  or  other  source,  after  being 
condensed  by  the  convex  lens  tti,  is  made  to  pass  through  the 
cylinder  n,  closed  with  plate-glass  ends,  and  filled  with  water. 
A  screen  is  placed  in  front  of  the  insolation  vessel,  to  prevent 
radiation  of  heat  from  the  body  of  the  observer ;  and  this, 
together  with  the  screen  L,  serves  also  to  prevent  radiation 
from  extenial  objects.  The  heat  evolved  in  the  insolation 
vessel  by  the  combustion  of  the  mixed  gases,  was  found  by 
direct  experiment,  not  to  exert  any  sensible  influence  on  the 
results.  All  the  parts  of  the  apparatus  between  a  and  I  are 
connected  by  ground-glass  joints  or  by  fusing;  no  caoutchouc, 
or  any  other  organic  matter,  which  could  be  acted  upon  by 
the  chlorine,  being  introduced,  excepting  in  those  parts  which 
merely  serve  to  carry  away  the  waste  gas. 

Fhoto-chemical  Induction, — On  exposing  the  gas  to  the  light, 
the  quantity  of  hydrochloric  acid  formed  does  not  at  once 
attain  the  maximum  :  a  certain  time  always  elapses  before  any 


PHOTO-CHEMICAL   INDUCTION.  493 

alteration  of  volume  is  perceptible;  a  slight  alteration  is, 
however,  soon  observed,  and  this  gradually  increases  till  the 
permanent  maximum  is  reached*  This  remarkable  fact  was 
first  observed  by  Draper,  who  explained  it  by  supposing  that 
the  chlorine  underwent,  by  exposure  to  light,  a  permanent 
allotropic  modification,  in  which  it  possessed  more  than  usually 
active  properties.  But  Bunsen  and  Roscoe  have  shown  that 
neither  chlorine  nor  hydrogen,  when  separately  insolated, 
undergoes  any  such  modification,  no  difference  being  indeed 
perceptible  between  the  action  of  light  on  a  mixture  of  the  gases 
which  have  been  separately  insolated  before  mixing,  and  on  a 
mixture  of  the  same  gases  evolved  and  previously  kept  in  the 
dark.  The  light  appears  then  to  act  by  increasing  the  attraction 
between  the  chemically  active  molecules,  or  by  overcoming 
certain  resistances  which  oppose  their  combination.  This 
peculiar  action  is  called  photo-chemical  induction. 

The  time  which  elapses  from  the  beginning  of  the  exposure 
till  the  maximum  action  is  attained,  varies  considerably  accord- 
ing to  circumstances,  the  maximum  being  sometimes  reached 
in  fifteen  minutes,  sometimes  in  three  or  four  minutes.  In 
one  instance,  the  first  action  was  visible  only  after  six  minutes' 
insolation,  whilst  in  some  experiments  a  considerable  action 
was  observed  in  the  first  minute. 

The  duration  of  the  inductive  action  varies  with  the  mass 
of  the  gas,  and  with  the  amount  of  light.  With  a  constant 
quantity  of  light,  it  increases  with  the  volume  of  the  exposed 
gas.  With  a  constant  volume  of  gas  it  is  found : — 1,  That  the 
time  necessary  to  effect  the  first  action  decreases  with  increase 
of  light,  and  in  a  greater  ratio  than  the  increase  of  light. — 

2.  That  the  time  which  elapses  until  the  maximum  is  attained, 
also  decreases  with  increase  of  light,  but  in  a  less  ratio. — 

3.  That  the  increase  of  the  induction  proceeds  at  first  in  an  ex- 
panding series,  and  then  converges  till  the  true  maximum  is 
attained. 

The  condition  of  increased  combining  power  into  which  the 
mixture  of  chlorine  and  hydrogen  is  brought  by  the  action  of 


494  CHEMICAL   ACTION    OF    LIGHT. 

light,  is  not  permanent ;  on  the  contrary,  the  resistance  to 
combination  overcome  by  the  influence  of  the  light,  is  soon 
restored  when  the  gas  is  allowed  to  stand  in  the  dark. 

The  resistance  to  combination  which  prevents  the  union  of 
the  gases  until  the  action  is  assisted  by  light,  may  be  increased 
by  various  circumstances,  especially  by  the  presence  of  foreign 
gases,  even  in  very  small  quantity.  An  excess  of  y^oT  ^^ 
hydrogen  above  that  contained  in  the  normal  mixture,  reduces 
the  action  from  100  to  38.  Oxygen,  in  quantity  amounting 
to  only  j-^-o  of  the  total  volume  of  gas,  diminishes  the  action 
from  100  to  4*7  ;  and  yoq-q  reduces  it  from  100  to  1'3.  An 
excess  of  Y^^  of  chlorine  reduces  the  action  from  100  to 
60-2;  and  f^  from  100  to  41-3.  A  small  quantity  of 
hydrochloric  acid  gas  does  not  produce  any  appreciable 
diminution ;  y^q-q  of  the  non-insolated  mixture  reduces  the 
action  from  100  to  55. 

■  The  increase  in  the  rate  at  which  combination  goes  on  up 
to  a  certain  point  under  the  influence  of  light,  appears  to  arise, 
not  from  any  peculiar  property  of  light,  but  rather  from  the 
mode  of  action  of  chemical  affinity  itself.  Chemical  induction 
is  in  fact  observed  in  cases  in  which  there  is  nothing  but  pure 
chemical  action  to  produce  the  alteration.  Thus,  when  a 
dilute  aqueous  solution  of  bromine  mixed  with  tartaric  acid  is 
left  in  the  dark,  hydrobromic  acid  is  formed  ;  and,  by  deter- 
mining the  amount  of  free  bromine  present  in  the  liquid  at 
different  times,  it  is  found  that  the  rate  at  which  the  produc- 
tion of  hydrobromic  acid  goes  on  is  not  uniform,  but  increases 
up  to  a  certain  point,  according  to  a  law  similar  to  that  which 
is  observed  in  photo-chemical  induction. 

These  phenomena  seem  to  point  to  the  conclusion  that  the 
affinity  between  any  two  bodies  is  in  itself  a  force  of  constant 
amount,  but  that  its  action  is  liable  to  be  modified  by  opposing 
forces,  similar  to  those  which  affect  the  conduction  of  heat  or 
electricity,  or  the  distribution  of  magnetism  in  steel.  We 
overcome  these  resistances  when  we  accelerate  the  formation 
of  a  precipitate  by  agitation,  or  a  decomposition  by  insolation. 


EXTINCTION   OF   THE   CHEMICAL   RAYS.  495 

Optical  and  Chemical  Extinction  of  the  Chemical  Rays, — 
When  light  passes  through  any  medium/  part  of  it  is  lost  by 
reflection  at  the  surface,  another  portion  by  absorption  within 
the  medium,  so  that  the  quantity  of  emergent  light  is  only  a 
fraction  of  the  incident  light.  This  is  true  with  regard  to  the 
chemical  as  well  as  to  the  luminous  rays.  By  passing  light 
from  a  constant  source  through  cylinders  with  plate-glass 
ends  filled  with  dry  chlorine,  it  is  found  that,  with  a  given 
length  of  cylinder,  the  quantity  of  the  chemical  rays  trans- 
mitted, when  no  chemical  action  takes  place,  is  to  the  quan- 
tity in  the  incident  light  in  a  constant  ratio  ;  in  other  words, 
the  absorption  of  the  chemical  rays  is  proportional  to  the  in- 
tensity of  the  light.  It  is  also  found  that  the  quantity  of 
chemical  rays  transmitted  varies  proportionally  to  the  density 
of  the  absorbing  medium. 

But  further,  when  light  passes  through  a  medium  in  which 
it  excites  chemical  action,  it  is  found  that,  in  addition  to  the 
optical  extinction  already  spoken  of,  a  quantity  of  light  is  lost 
proportional  to  the  amount  of  chemical  action  produced.  The 
depth  of  pure  chlorine  at  0°  C  and  0*76  mm.  pressure,  through 
which  the  light  of  a  coal-gas  flame  must  pass  in  order  to  be 
reduced  to  ^,  is  found  to  be  173*3  millimeters.  Hence, 
since  the  quantity  of  light  absorbed  varies  as  the  density,  the 
depth  of  chlorine  diluted  with  an  equal  volume  of  air,  or  other 
chemically  inactive  gas,  required  to  produce  the  same  amount 
of  extinction,  would  be  346*6  mm.  But  when  the  sensitive 
mixture  of  equal  volumes  of  chlorine  and  hydrogen  is  used, 
the  depth  of  the  mixture  which  the  light  must  penetrate  to  be 
reduced  to  J^-,  is  found  to  be  only  234  mm.  Hence,  it  appears 
that  light  is  absorbed  in  doing  chemical  work. 

With  light  from  other  sources,  results  are  obtained  similar 
in  character,  but  differing  in  amount.  Diffuse  morning  light 
reflected  from  the  zenith  of  a  cloudless  sky  is  reduced  to  -^^ 
by  passing  through  45 '6  mm.  of  chlorine,  and  through  73*5 
mm.  of  the  sensitive  mixture  ;  diffuse  evening  light  is  reduced 
to  j\  by  passing  through  19*7  mm.  of  chlorine  and  through 


496  ELECTRICITY. 

57*4  mm.  of  the  standard  mixture.  Hence  it  appears  that 
the  chemical  rays  of  diffuse  morning  light  are  absorbed  by 
chlorine  much  more  quickly  than  those  of  lamp-light ;  and 
those  of  evening  light  with  still  greater  facility.  From  this 
we  may  conclude  that  the  chemical  rays  reflected  at  different 
times  and  hours,  possess,  not  only  quantitative  but  also  quali- 
tative differences,  similar  to  the  various  coloured  rays  of  the 
visible  spectrum.  It  is  a  fact  well  known  to  photographers, 
that  the  amount  of  light  photometrically  estimated  gives  no 
measure  of  the  time  in  which  a  given  photochemical  effect  is 
produced.  For  the  taking  of  pictures,  a  less  intense  morning 
light  is  always  preferred  to  a  bright  evening  light. 


ELECTRICITY. 


Measurement  of  the  Force  of  Electric  Currents,  —  There  are 
two  methods  by  which  the  forces  of  electric  currents  are  com- 
pared with  each  other,  viz.,  the  chemical  or  electrolytic,  and 
the  electromagnetic  methods. 

Faraday  has  shown  that  the  amount  of  chemical  work  done 
is  the  same  in  all  parts  of  the  circuit ;  that,  if  two  decomposing 
cells  be  introduced,  one  containing  dilute  sulphuric,  the  other 
hydrochloric  acid,  the  quantity  of  hydrogen  evolved  is  the 
same  in  both,  and  equal  to  the  hydrogen  evolved  (by  true 
current  action)  in  each  cell  of  the  battery ;  moreover,  that 
the  quantities  of  different  elements  eliminated  in  any  part  of 
the  circuit,  are  always  in  the  ratio  of  their  equivalent  weights. 
The  voltameter  (I.  290)  affords,  therefore,  a  true  and  exact 
measure  of  the  amount  of  the  chemical  or  electrical  force 
developed  by  the  battery.  But  its  indications  are  not  always 
sufficiently  rapid.  In  fact,  in  using  this  instrument,  it  is 
necessary  to  wait  till  a  measurable  quantity  of  gas  is  collected. 
It  will,  therefore,  indicate  the  relative  quantity  of  electricity 


THE   TANGENT   COMPASS. 


497 


which  has  passed  through  the  circuit  in  a  certain  j&nite  inter- 
val, say  in  a  minute;  but  it  gives  no  information  of  any 
variations  that  may  have  taken  place  during  that  interval ; 
moreover,  it  can  only  be  used  to  measure  currents  of  con- 
siderable strength. 


The  Tangent-compass, — To  supply  these  deficiencies,  and 
obtain  exact  and  instantaneous  indications  of  the  relative 
forces  of  electric  currents,  recourse  is  had  to  the  electro- 
magnetic method,  which  consists  in  observing  the  deflection 
of  a  magnetic  needle  produced  by  the  current.  Instruments 
for  this  purpose  are  called  Galvanometers  or  Rheometers,  The 
effect  of  a  coil  of  wire  in  intensifying  the  effect  of  the  current 
upon  a  magnetic  needle,  is  described  at  page  290.  Vol.  I.,  of 
this  work.  But  the  kind  of  instrument  there  described, 
though  commonly  called  a  galvanometer,  is  really  only  a 
galvanoscope,  or  multiplier.  It  indicates  with  great  delicacy 
the  existence  and  direction  of  an  electric  current,  but  it  is  not 
constructed  for  quantitative  determinations. 

In  the  true  galvanometer  (Fig.  41)  the  current,  instead  of 
passing  through  a  long  coil  of  wire  placed  close  to  the  needle, 
is  made  to  pass  through  a  broad 
circular  band  of  brass  or  copper, 
p  Q,  of  considerable  dimensions,  in 
the  centre  of  which  is  placed  a  mag- 
netic needle,  n,  the  length  of  which 
is  very  small  in  comparison  with 
the  diameter  of  the  circular  con- 
ductor, so  that  the  distance  of  the 
extremity  of  the  needle  from  the 
conductor  P  Q,  and  consequently 
the  force  exerted  upon  it  by  the  cur- 
rent, is  sensibly  the  same  at  all 
angles  of  deflection.  The  instrument 


498 


ELECTRICITY. 


is  so  placed  that  the  plane  of  the  circle  P  Q  coincides  with  the 
magnetic  meridian.  To  determine  the  relation  which  exists 
under  these  circumstances  between  the  deflection  of  the 
needle  and  the  force  of  the  current,  let  p  q  (Fig.  42)  repre- 
sent the  circular  conductor  seen  from  above ;  a  z  the  direction 
of  the  needle  under  the  influence  of  the  current.  The  extre- 
mity of  the  needle  is  then  acted  upon  by  two  forces,  viz,  the 
force  of  terrestrial  magnetism  acting  Fijr.  42. 

parallel  to  P  Q,  and  the  force  of 
the  current  acting  at  right  angles  to 
that  direction.  Let  these  forces  be 
represented  in  magnitude  and  direc- 
tion by  the  lines  ah,  a  c.  Draw 
also  the  line /a  d  perpendicular  to 
a  z,  and  hf,  c  d,  perpendicular  to  df. 
Then  the  lines  af,  a  d  represent  the 
resolved  portions  of  the  forces  a  b, 
a  c,  which  act  at  right  angles  to  the 
needle,  and  tend  to  turn  it  one  way 
or  the  other.  In  order,  therefore, 
that  the  needle  may  be  at  rest,  a  d 
must  be  equal  to  af,  or 

a  c  .  cos    c  a  d  =  ah,  sin  ah  f. 

Now  the  angle  c  a  cZ  is  equal  to  v, 

the  angle  of  deflection  of  the  needle 

from  the  meridian,  because  a  c  is 

perpendicular  to  p  Q,  and  a  d  to  a  z ;  and  the  angle  a  h  f 

is  also  equal  to  u,  because  a  6  is  parallel  to  p  Q,  and  hfXo  a  z. 

Hence  the  preceding  equation  becomes 


a  c 


sin  V 


therefore 


cos  V  ^  a  h 
a  c  :=  a  h  ,  tan  v. 

Or,  if  we  denote  the  force  of  the  earth's  magnetism  by  M,  and 
that  of  the  electric  current  by  E,  we  have 

E  =  M  tan  v. 


ohm's  formulae.  499 

Consequently,  since  the  magnetic  force  of  the  earth  is  constant 
at  the  same  place  (at  least  for  short  intervals  of  time),  the 
magnetic  force  of  the  current  is  proportional  to  the  tangent  of  the 
angle  of  deflection :  hence  the  name  of  the  instrument. 

Comparison  between  the  chemical  and  magnetic  actions  of 
the  current,  —  By  introducing  into  the  same  voltaic  curcuit,  a 
voltameter  and  a  tangent-compass,  it  is  found  that  the  chemical 
action  of  the  current  is  directly  proportional  to  its  magnetic 
action.  The  tangent-compass  affords,  therefore,  a  measure  of 
the  chemical  as  well  as  of  the  magnetic  force  of  the  current, 
the  quantity  of  chemical  or  electrical  force  in  the  circuit 
being  proportional  to  the  tangent  of  the  angle  of  deflection  of 
the  needle. 

If  m  milligrammes  of  hydrogen  are  evolved  in  a  second 
in  the  voltameter,  when  the  galvanometer  exhibits  a  de- 
flection of  45°,  and  therefore  a  current  force  =  1  (since 
tan  45°  =  1),  then,  when  the  same  galvanometer  shows  a 
deflection  =  a,  the  quantity  of  hydrogen  evolved  in  t 
seconds  will  be  m  .  ^  .  tan  a.  The  quantity  of  any  other 
element  eliminated  in  the  same  circuit,  will  be  found  by 
multiplying  this  quantity  by  the  equivalent  weight  of  that 
element. 

With  a  tangent -compass,  the  diameter  of  whose  conductor 
measures  one  decimeter,  it  is  found  that,  when  the  deflection 
is  45°,  one  milligramme,  or  11*2  cubic  centimeters  (at  0°  C. 
and  Bar.  0*76  met.)  of  hydrogen  is  eliminated  in  32*3  seconds. 
Hence  with  any  other  circular  current  whose  radius  is  r  deci- 
meters and  force  =  tan  ot,  the  time  t  in  which  1  milligramme 
of  hydrogen  is  evolved,  or  9  milligrammes  of  water  are 
decomposed,  is 

32-3 


t  = 


tan  et 


OhrrCs  Formulce.  —  The  amount  of  electrical  or  chemical 
power  developed  in  the  voltaic  circuit,  —  or,  in  other  words. 


500  ELECTRICITY. 

the  quantity  of  electricity  which  passes  through  a  transverse 
section  of  the  circuit,  in  a  unit  of  time,  evidently  depends 
upon  two  conditions ;  viz.,  the  power,  or  electromotive  force 
of  the  battery,  and  the  resistance  offered  to  the  passage  of  the 
current  by  the  conductors,  liquid  or  solid,  which  it  has  to 
traverse.  With  a  given  amount  of  resistance,  the  power  of 
the  battery  is  proportional  to  the  quantity  of  electricity  deve- 
loped in  a  given  time ;  and  by  a  double  or  treble  resistance, 
we  mean  simply  that  which,  with  a  given  amount  of  exciting 
power  in  the  battery,  reduces  the  quantity  of  electricity  deve- 
loped, or  work  done,  to  one-half  or  one-third.  If,  then,  we 
denote  the  electromotive  force  of  the  battery  by  Ey  and  the 
resistance  by  72,  we  have,  for  the  quantity  of  electricity  pass- 
ing through  the  circuit  in  a  unit  of  time,  the  expression  : 

^=i w 

This  is  called  Ohm's  law,  from  the  name  of  the  distinguished 
mathematician  who  first  announced  it.  It  must  be  under- 
stood, not  as  a  theorem,  but  as  a  definition.  To  say  that  the 
strength  of  the  current  varies  directly  as  the  electromotive 
force,  and  inversely  as  the  resistance,  is  simply  to  define 
what  we  mean  by  electromotive  force  and  what  we  mean  by 
resistance.* 

Let  us  now  endeavour,  by  means  of  the  formula  (1),  to 
estimate  the  effect  produced  on  the  strength  of  the  current 
by  increasing  the  number  and  size  of  the  plates  of  the  battery. 
The  resistance  R  consists  of  two  parts ;  viz.  that  which  the 
current  experiences  in  passing  through  the  cells  of  the  battery 
itself,  and  that  which  is  offered  by  the  external  conductor 
which  joins  the  poles.  This  conductor  may  consist  either  wholly 
of  metal,  or  partly  of  metal  and  partly  of  electrolytic  liquids. 

♦  It  must  be  remembered  that  we  are  here  merely  comparing  the  strength 
of  electric  currents  one  with  the  other,  not  reducing  the  current  force  to  ab- 
solute mechanical  measure,  or  even  comparing  it  with  the  electro-static  forces 
of  attraction  and  repulsion.    (See  page  506.) 


ohm's  formula.  501 

Let  the  resistance  within  the  battery  be  r,  and  the  external 
resistance  v' ;  then,  in  the  one-celled  battery,  we  have 

1  =  VT^ (2) 

Now  suppose  the  battery  to  consist  of  n  cells  perfectly  similar ; 
then  the"  electromotive  force  becomes  nE,  the  resistance  within 
the  battery  nri  if,  then,  the  external  resistance  remains  the 
same,  the  strength  of  the  current  will  be  denoted  by 
nE  E 


nr  -\-  t'  ,    r' 

r  +- 
n 


(3) 


If  r'  be  small,  this  expression  has  nearly  the  same  value 

jp 
as    ^ ;  that  is  to  say,  if  the  circuit  be  closed  by  a  good 

conductor,  such  as  a  short  thick  wire,  the  quantity  of  elec- 
tricity developed  by  the  compound  battery  of  n  cells,  is 
sensibly  the  same  as  that  evolved  by  a  single  cell  of  the  same 
dimensions.  But  if  r'  is  of  considerable  amount,  as  when  the 
circuit  is  closed  by  a  long  thin  wire,  or  when  an  electrolyte  is 
interposed,  the  strength  of  the  current  increases  considerably 
with  the  number  of  plates.  In  fact,  the  expression  (3)  is 
always  greater  than  (2)  ;  for  — 

nE         __         E         ^  {n  -I)  Er" 

^  ^  _l_  /  7*  +  r'  (nr  -^  r')(r  -\-  r') ' 

a  quantity  which  is  necessarily  positive  when  n  is  greater 
than  unity. 

Suppose,  in  the  next  place,  that  the  size  of  the  plates  is 
increased,  while  their  number  remains  the  same.  Then, 
according  to  the  chemical  theory,  an  increase  in  the  surface  of 
metal  acted  upon  must  produce  a  proportionate  increase  in  the 
quantity  of  electricity  developed,  provided  the  conducting 
power  of  the  circuit  is  sufficient  to  give  it  passage.  According 
to  the  theory  which  attributes  the  development  of  the  elec- 

VOL.  II.  N  N 


502  ELECTRICITY. 

tricity  to  tlie  contact  of  dissimilar  metals,  an  increase  in  tlie 
size  of  the  plates  does  not  increase  the  electromotive  force, 
but  it  diminishes  the  resistance  within  the  cells  of  the  battery 
by  offering  a  wider  passage  to  the  electricity.  Hence  in  the 
single  cell,  if  the  surface  of  the  plates,  and  therefore  the  trans- 
verse section  of  the  liquid,  be  increased  m  times,  the  expression 
for  the  strength  of  the  current  becomes 

E  _  mE 

r    ,     ,  •  r  -\-  mr^' 

—  4-  r 

m 

If  /  be  small,  this  expression  is  nearly  the  same  as ,, 

that  is  to  say,  the  quantity  of  electricity  in  the  current  in- 
creases very  nearly  in  the  same  ratio  as  the  size  of  the  plates ; 
but  when  the  external  resistance  is  considerable,  the  advantage 
gained  by  increasing  the  size  of  the  plates  is  much  less. 

We  may  conclude,  then,  that  when  the  resistance  in  the 
circuit  is  small,  as  in  electro-magnetic  experiments,  a  small 
number  of  large  plates  is  the  most  advantageous  form  of 
battery ;  but  in  overcoming  great  resistances,  power  is  gained 
by  increasing  the  number  rather  than  the  size  of  the  plates. 

Electric  Resutance  of  Metals.  —  The  preceding  principles 
enable  us  to  determine  the  manner  in  which  the  resistance  of 
a  metallic  wire  varies  with  its  length.  For  this  purpose 
suppose  a  one-celled  battery  (Daniell's)  to  be  used,  which 
maintains  a  constant  action  during  the  time  of  the  experiment. 
First  let  the  current  be  made  to  pass  directly  through  the. 
tangent- compass,  and  afterwards  let  wires,  of  uniform  thick- 
ness and  of  the  lengths  of  5,  10,  40,  70,  and  100  meters,  be 
interposed  in  the  circuit,  and  the  resulting  deflections  ob- 
served. Now,  as  the  force  of  the  battery  is  constant,  the 
resistance  is  inversely  as  the  strength  of  the  current.  But 
the  total  resistance  is  made  up  of  that  of  the  interposed  wires, 
together  with  that  of  the  battery  itself,  and  that  of  the  con- 
ductor of  the  tangent-compass.      These  last  two  resistances 


ELECTRIC   RESISTANCE   OF   METALS. 


503 


we  may  suppose  to  be  equal  to  that  of  a  wire  of  the  same 
thickness  as  the  above,  and  of  a  certain  unknown  length,  x. 
Instead,  therefore,  of  the  lengths  of  wire  5,  10,  40,  &c.,  we 
must  substitute  x  +  5^  os  +  \0,  x  +  AOy  &c.  An  experiment 
of  this  kind*  gave  the  following  results :  — 


Length  of  Wire. 

Observed  Deflection. 

Tangent  of  Deflection. 

X  meters 

62°     0' 

1-880 

X  +       5 

40     20 

0-849 

X  +     10 

28     30 

0  543 

x  +     40 

9     45 

0-172 

X  +      Id 

6        0 

0-105 

X  +   100 

4     15 

0074 

Now,  let  us  assume,  as  most  probable,  that  the  resistance 
of  a  wire  increases  in  direct  proportion  to  its  length,  then, 
according  to  Ohm's  law,  the  first  two  experiments  give :  — 

^   :   ^  +  5   =   0-849    :    1*880 

whence,  x  =  4*11.  And,  by  combining  in  a  similar  manner 
the  first  experiment  with  all  the  others,  we  obtain  for  x  the 
several  values  4*06,  4*03,  4*14,  4*09,  the  mean  of  the  whole 
being  4-08.  Substituting  this  value  for  x  in  the  preceding 
table,  and  calculating  the  corresponding  deflections  on  the 
supposition  that  the  strength  of  the  current  varies  inversely 
as  the  resistance,  that  is  as  the  length  of  the  conductor,  we 
obtain  the  following  results :  — 


Length  of 
Conductor. 

Calculated 
Deflection. 

Observed 
Deflection. 

Difference. 

4-08  meters 

62°      0' 

62°     0' 

9-08 

40      18 

40     20 

+      2' 

14-08 

28      41 

28     30 

-   11 

44-08 

9      56 

9     45 

-   11 

7408 

5     57 

6       0 

+     3 

104-08 

4     14 

4     15 

+      1 

*  Miiller,  Lehrbuch  der  Physik.  1853,  ii.  177. 

NN  2 


504  ELECTRICITY. 

From  the  results  of  this  and  similar  experiments,  it  is 
inferred  that — the  resistance  of  a  conductor  of  uniform  thickness 
varies  directly  as  its  length. 

The  Rheostat  or  Current-regulator, — The  various  forms  of 
the  so-called  constant  battery,  Daniell's  for  example  (I.  284), 
attain  their  end  but  imperfectly,  a  galvanometer  included  in 
the  circuit  always  exhibiting  more  or  less  variation.  A  really 
constant  current  can  only  be  obtained  by  interposing  in  the 
circuit  a  conducting  wire  of  variable  length,  so  that  the 
resistance  may  be  increased  or  diminished  as  the  action  of  the 
battery  becomes  stronger  or  weaker.  Various  instruments 
have  been  contrived  for  this  purpose.  The  one  most  used, 
invented  by  Professor  Wheatstone,  is  represented  in  fig.  43. 
A  and  B  are  two  cylinders  of  the  pjg,  43. 

same  dimensions  —  the  first  of 
dry  wood,  the  second  of  brass  — 
placed  with  their  axes  parallel 
to  each  other.  The  wooden 
cylinder  A  has  a  fine  screw 
cut  on  its  surface,  and  around 
it,  following  tlie  thread  of  the 
screw,  is  coiled  a  thin  ht^ss 
wire.  One  extremity  of  this  wire 
is  attached  to  a  brass  ring,  r,  at  the  nearer  end  of  the  wooden 
cylinder,  and  the  other  to  the  farther  extremity  of  the  brass 
cylinder.  The  ring  v  and  the  nearer  end  of  the  brass  cylin- 
der are  connected  with  the  wires  of  the  battery  through 
the  medium  of  the  screw-joints  CD.  A  movable  handle, 
/i,  serves  to  turn  the  cylinders  alternately  round  their  axes. 
By  turning  b  to  the  right,  the  wire  is  uncoiled  from  A  and 
coiled  upon  B ;  and  the  contrary  when  A  is  turned  to  the  left. 
The  number  of  coils  of  wire  upon  A  are  indicated  by  a  scale 
placed  between  the  cylinders,  the  fractions  of  a  turn  being 
measured  by  an  index  moving  round  the  ring  v,  which  is 
graduated  accordingly.     As  the  coils  of  the  wire  are  insulated 


THE   KHEOSTAT.  505 

on  the  wooden  cylinder,  but  not  on  the  brass,  it  is  evident 
that  the  path  of  the  current  will  be  longer,  and  therefore  the 
resistance  greater,  in  proportion  to  the  number  of  coils  of  wire 
upon  the  wooden  cylinder. 

By  means  of  the  rheostat  and  the  tangent-compass,  the 
resistances  afforded  by  different  conductors  to  the  passage  of 
the  current  may  be  measured  with  great  facility.  Suppose 
that  when  the  wire  of  the  rheostat  is  completely  uncoiled 
from  the  wooden  cylinder  (the  index  then  standing  at  0°),  a 
tangent-compass  introduced  into  the  circuit  shows  a  deflection 
of  46°.  Then  let  a  copper  wire  four  yards  long  and  -^ih  of 
an  inch  thick,  be  introduced  into  any  part  of  the  same  circuit. 
The  galvanometer-needle  will  then  exhibit  a  smaller  deflection, 
say  37°.  On  removing  the  wire,  the  galvanometer  will  again 
exhibit  its  former  deflection  of  46°.  Now  let  the  rheostat  wire 
be  coiled  round  the  wooden  cylinder  till  the  needle  returns  to 
37°,  and  suppose  that  to  produce  this  effect  twenty  turns 
of  the  rheostat  wire  are  necessary.  This  length  of  the 
rheostat  wire  produces  a  resistance  equal  to  that  of  the  wire 
under  examination.  Next  let  a  similar  experiment  be  made 
with  a  wire  of  the  same  length  but  of  twice  the  thickness,  and 
consequently  having  a  transverse  section  four  times  as  great 
as  that  of  the  former.  It  will  be  found  that  five  turns  of  the 
rheostat  wire,  or  one-fourth  of  the  former  length,  are  sufficient 
to  produce  a  resistance  equal  to  that  of  the  second  wire.  By 
experiments  thus  conducted  it  is  found  that:  The  resistance 
of  a  wire  or  any  other  conductor  of  given  length  varies  inversely 
as  its  transverse  section.  And  comparing  this  result  with  that 
which  was  established  at  page  503,  we  find  that :  Conductors 
of  the  same  inaterial  offer  equal  resistances,  when  their  lengths 
are  to  one  another  in  the  same  proportion  as  their  transverse 
sections. 

In  a  similar  manner,  the  relative  conducting  powers  of 
different  metals  may  be  ascertained.  Taking  the  resistance 
of  pure  copper  as  the  unit,  it  is  found  that  that  of  iron  is 

N  N    3 


506  ELECTRICITY. 

7*02,  of  brass  3*95,  of  German  silver  15-47.     The  conducting 
powers  are  of  course  inversely  as  these  numbers  (II.  441). 

Heating  Power  of  the  Voltaic  Current,  —  The  degree  of  heat 
excited  in  a  metallic  wire  by  the  passage  of  the  current, 
increases  with  the  strength  of  the  current  and  with  the 
resistance  of  the  wire.  To  determine  the  numerical  relations 
of  this  phenomenon,  the  wire  to  be  heated  is  formed  into  a 
spiral  and  enclosed  within  a  vessel  containing  strong  alcohol, 
or  some  other  non-conducting  liquid,  in  order  that  the  cur- 
rent may  pass  entirely  through  the  wire,  and  not  through  the 
liquid  itself.  The  rise  of  temperature  in  the  liquid  is  noted 
by  a  delicate  thermometer ;  the  strength  of  the  current  mea- 
sured by  the  tangent-compass ;  and  the  resistance  of  the  wire 
afterwards  determined  in  the  manner  above  described.  By 
this  method  Lenz*  has  shown  that:  — 

The  quantity  of  heat  evolved  in  a  given  time  is  directly  propor- 
tioned to  the  resistance  of  the  wire,  and  to  the  square  of  the  quan- 
tity of  electricity  lohich  passes  through  it. 

The  same  result  has  been  obtained  by  Joule  f,  both  for 
wires  and  liquid  conductors  ;  by  E.  Becquerel  for  liquids  ;  and 
by  RiessJ  for  the  heat  produced  by  the  discharge  of  the 
electricity  accumulated  in  a  Leydcn  jar. 

Reduction  of  the  Force  of  the  Current  to  absolute  mechanical 
Measure:  —  This  important  determination  has  been  made  the 
subject  of  an  extensive  research  by  Weber  and  Kohlrausch.  § 
To  understand  tlio  results  obtained  by  these  philosophers,  it  is 
necessary  to  define  exactly  the  several  units  of  measurement 
adopted : 

a.  The  unit  of.  electric  fluid  is  the  quantity  which,  when 
concentrated  in  a  point,  and  acting  on  an  equal  quantity  of 

*  Pogg.  Ann.  Ixi.  18.  f  Phil.  Mag.  [3],  xix.  210. 

X  Pogg.  Ann.  xl.  335  ;  xliil  47  ;  xlv.  1. 

§  Abhandlungen  derMathematisch-physischcn  Classe  der  Kiinigl.  Sachsis- 
chen  Gescllsch.  d.  Wiss.     Leipzig.  1856. 


FORCE  OF  THE  VOLTAIC  CURRENT  MEASURED.   507 

the  same  fluid  also  concentrated  in  a  point,  and  at  the  unit  of 
distance,  exerts  a  repulsion  equal  to  the  unit  of  force. 

b.  The  unit  of  electrochemical  intensity  is  the  force  of  the 
current  which,  in  a  unit  of  time,  decomposes  a  unit  of  weight 
of  water,  or  an  equivalent  quantity  of  any  other  electrolyte. 

c.  The  unit  of  electromagnetic  force,  is  the  force  of  a 
current  which — when  it  traverses  a  circular  conductor 
whose  area  is  equal  to  the  unit  of  surface,  and  acts  upon  a 
magnet  whose  magnetic  moment  is  equal  to  unity,  the  magnet 
being  placed  at  a  great  distance,  and  In  such  a  manner  that 
its  axis  is  parallel  to  the  plane  of  the  conductor,  and  its  centre 
on  a  line  drawn  through  the  centre  of  the  circular  conductor, 
and  perpendicular  to  its  plane  —  exerts  upon  the  magnet  a 
rotatory  force  equal  to  unity  divided  by  the  cube  of  the  dis- 
tance between  the  centre  of  the  needle  and  the  centre  of  the 
conductor. 

"Weber  had  shown  by  previous  experiments  that  the  unit  of 
electrochemical  force  is  to  that  of  electromagnetic  force  as 
106f  to  1.  It  remained,  therefore,  to  determine  the  relation 
between  the  electromagnetic  unit  and  the  electrostatic  unit 
(1),  and  thus  to  establish  a  numerical  relation  between  statical 
and  dynamical  electricity.  The  mode  of  experimenting  was 
as  follows :  — 

1.  A  Leyden  jar  having  been  strongly  charged,  its  knob 
was  touched  with  a  large  metallic  ball,  which  took  from  it  a 
certain  portion  of  its  charge,  determined  by  previous  experi- 
ments. The  charge  of  the  ball  was  then  transferred  to  the 
torsion-balance,  and  the  repulsive  force  measured.  At  the 
same  time,  the  remainder  of  the  charge  of  the  jar  was  made  to 
traverse  the  wire  of  a  galvanometer,  previously,  however, 
having  been  passed  through  a  long  column  of  water,  in  order 
to  give  it  a  sensible  duration,  and  prevent  it  from  passing 
from  one  coil  of  the  wire  to  another  in  the  form  of  a  spark. 
In  this  manner,  a  relation  was  established  between  the  statical 
and  dynamical  effects  of  the  charge  of   the  jar. — 2.    The 

N  N  4 


508  ELECTRICITY. 

intensity  and  duration  of  a  voltaic  current  were  determined, 
which  imparted  to  the  galvanometer  needle  the  same  deflection 
as  that  produced  hy  the  discharge  of  the  Ley  den  jar. 

The  results  of  the  experiments  were  as  follows:  — 

Through  each  section  of  a  conductor  traversed  by  a  current 
whose  force  is  equal  to  the  electromagnetic  unit,  there  passes 
in  a  second  of  time  a  quantity  of  positive  electricity  equal  to 
155,370  X  10^  statical  units  (p.  506,  a),  and  an  equal  quantity 
of  negative  electricity  travelling  in  the  opposite  direction. 

The  quantity  of  electricity  required  to  decompose  one 
milligramme  of  water,  amounts  to  106f  times  this  quantity, 
or  16,573  x  10^  units  of  electricity,  of  each  kind.  To  decom- 
pose nine  milligrammes  of  water,  or  one  equivalent,  requires 
of  course  nine  times  this  amount  of  electricity.  This  quantity 
of  positive  electricity  (9  x  16,573  x  10^)  accumulated  on  a 
cloud  situated  1000  meters  above  the  surface  of  the  earth,  and 
acting  on  an  equal  quantity  of  negative  electricity  on  the 
surface  of  the  earth  below  the  cloud,  would  exert  an  attrac- 
tive force  equal  to  226,800  kilogrammes,  or  208  tons. 

From  the  same  data  it  is  calculated  that,  if  all  the  particles 
of  hydrogen  in  one  milligramme  of  water  in  the  form  of  a 
column  one  millimeter  long,  were  attached  to  a  thread,  and 
all  the  particles  of  oxygen  to  another  thread,  then,  to  effect  the 
decomposition  of  the  water  in  a  second,  the  two  threads  would 
require  to  be  drawn  in  opposite  directions,  each  with  a  force 
of  147,380  kilogrammes,  or  145  tons.  If  the  water  were 
decomposed  with  less  velocity,  the  tension  would  be  propor- 
tionally less. 


509 


CHEMICAL    NOTATION    AND    CLASSIFICATION. 


ATOMS   AND   EQUIVALENTS. 

Equivalent  quantities  of  any  two  substances  are  such  as 
can  replace  one  another  in  combination,  producing  compounds 
of  similar  chemical  character.  Thus,  when  copper  is  immersed 
in  a  solution  of  nitrate  of  silver,  31*7  parts  of  copper  take  the 
place  of  108  parts  of  silver,  forming  a  neutral  nitrate  of 
copper.  Similarly,  the  31*7  parts  of  copper  may  be  replaced 
by  32*5  parts  of  zinc,  and  these  again  by  39  parts  of  potassium, 
the  product  of  the  substitution  being  in  each  case  a  neutral 
salt.  These  quantities  of  silver,  copper,  zinc,  and  potassium, 
are  therefore  equivalent  to  one  another :  they  discharge 
analogous  chemical  functions.  In  like  manner,  47  parts  of 
potash,  and  31  parts  of  soda  are  equivalent,  because  they 
unite  with  the  same  quantity  of  an  acid  to  form  neutral  salts. 
Equivalent  numbers  cannot,  however,  be  always  determined 
by  actual  substitution.  Six  parts  of  carbon  are  said  to  be 
equivalent  to  14  parts  of  nitrogen;  but  there  is  no  known 
instance  of  the  direct  replacement  of  nitrogen  by  carbon. 
Moreover,  certain  quantities  of  sulphuric  acid  and  soda  are 
spoken  of  as  equivalent  to  one  another,  although  it  is  plainly 
impossible  that  bodies  so  opposite  in  character  should  dis- 
charge the  same  chemical  function.  In  fact,  the  term  equi- 
valent is  frequently  used,  not  in  its  strict  etymological  sense, 
but  as  synonymous  with  combinirig  number.  Eight  parts  of 
oxygen  are  said  to  be  equivalent  to  1  part  of  hydrogen,  because 
the  bodies  unite  in  this  proportion  to  form  water  (I.  123). 
This  confusion  of  the  terms  equivalent  and  combining  number. 


510  .       CHEMICAL    NOTATION. 

arises  from  tlie  circumstance  that  the  combining  numbers  in 

o 

most  general  use  have  been  selected  so  as  to  represent,  in 
many  cases,  the  true  equivalents.  Nevertheless,  the  ideas  of 
equivalent  and  combining  proportion  are  essentially  different, 
and  the  numbers  which  relate  to  them  cannot  be  made  to 
coincide  in  all  cases.  The  numbers  which  represent  the  pro- 
portions in  which  bodies  combine,  though  to  a  certain  extent 
arbitrary,  may  be  regarded  as  fixed  when  once  selected ;  but 
the  equivalent  of  a  body  varies  according  to  the  chemical 
function  which  it  discharges.  When  iron  dissolves  in  hydro- 
chloric acid,  producing  ferrous  chloride,  FeCl,  every  grain  of 
hydrogen  expelled  from  the  acid  is  replaced  by  28  grains  of  iron; 
but  when  the  same  metal  dissolves  in  aqudregia,  forming  ferric 
chloride,  FcgClg  or  Fe^Cl,  each  grain  of  hydrogen  in  the  acid  is 
replaced  by  18^  grains  of  iron ;  in  other  words,  the  equivalent 
of  iron  (H  =  1)  is  28  in  the  ferrous  acid,  18f  in  the  ferric 
compounds.  Similarly,  the  equivalent  of  mercury  is  200  in  the 
mercurous,  100  in  the  mercuric  compounds.  By  comparing  the 
perchlorates  with  the  permanganates,  it  appears  that  55*7  parts 
of  manganese  are  equivalent  to  35*5  parts  of  chlorine.  Now 
this  same  quantity  of  chlorine  is  equivalent  to  8  parts  of 
oxygen,  and  to  16  parts  of  sulphur  :  moreover,  the  analogy  of 
the  sulphates  and  manganates  shows  that  16  parts  of  sulphur 
are  equivalent  to  27*7  parts  of  manganese,  i.  e,  half  the  former 
quantity.  Lastly,  by  comparing  the  manganous  with  the 
manganic  salts,  it  appears  that  if  the  equivalent  of  man- 
ganese be  27*7  in  the  former,  it  must  be  18*5  in  the  latter. 
Manganese  has,  therefore,  three  different  equivalents, 
according  to  the  kind  of  compound  into  which  it  enters ; 
and,  generally,  the  number  of  equivalents  which  may  be 
assigned  to  a  body  is  equal  to  the  number  of  chemical  func- 
tions which  it  discharges. 

The  so-called  tables  of  equivalents  are  really,  as  already 
observed,  tables  of  combining  proportion.  How  are  these 
combining  proportions  determined  ?     Most  bodies  unite  with 


ATOMS   AND  EQUIVALENTS.  511 

others  in  more  than  one  proportion.     Eight  parts  of  oxygen 
combine  with   14,  7,  4*7,   3*5,  and   2*8   parts   of  nitrogen. 
Which  of  these  numbers  is  to  be  taken  as  the  combining 
number  of  nitrogen?     Again, — 1   part  of  hydrogen  unites 
with  4|-  parts  of  nitrogen,  and  yet  the  combining  number  of 
nitrogen  (H  =  1),  is  said  to  be  not  4f,  but  three  times  that 
number,  viz.  14.     Why  is  this  last  number  adopted?      The 
solution  of  such  questions  leads  to  a  variety  of  considerations. 
Obviously,  the  combining  numbers  should  be  so  selected  as  to 
represent  all  series  of  compounds  by  the  simplest  formulae, 
and  to  express  analogous  combinations  by  similar  formulae. 
Practically,  however,  this  rule  is  not  found  to  be  a  sufficient 
guide  in  all  cases ;  and,  in  the  actual  determination  of  com- 
bining numbers,  reference  is  constantly  made  to  considerations 
intimately  related  to  the  atomic  theory,  such  as  isomorphism, 
the  specific  heat  of  atoms,  vapour-densities,  and  the  basicity 
of  acids.     Suppose,  for  example,  the  combining  number  of  an 
acid  is  to  be  determined ;  the  first  thing  to  be  ascertained  is  its 
saturating  pow-er.     But  then  arises  the  question, — is  the  acid 
monobasic,  bibasic,  or  tribasic  ?     Now,  on  the  system  of  com- 
bining numbers  or  equivalents,  viewed  without  reference  to 
atomic  constitution,  such  a  question  has  no  meaning.     Why, 
for  example,  is  citric  acid  said  to  be  tribasic  ?     Because  the 
formula  of  a  neutral  citrate  is  C12M3O14 ;  a  formula  which 
does  not  admit  of  division  by  3,  without  introducing  a  frac- 
tional number  of  oxygen-atoms.     But  if  the  symbols  merely 
denote  combining  numbers  or  equivalents,  there  can  be  no 
valid  objection  to  the  use  of  such  fractional  numbers.     There 
is  nothing  absurd  in  the  idea  of  ^  of  the  quantity  of  oxygen 
which  unites  with  one  pound  of  hydrogen  to  form  water. 
But  if  the  symbols  denote  atoms,  the  case  is  altered,  the  idea 
of  a  divided  atom  being  self-contradictory. 

This  is  but  one  instance  out  of  many  of  the  influence  exerted 
by  the  atomic  theory  on  the  construction  of  chemical  formulae, 
and  consequently  on  the  determination  of  combining  numbers. 


512  CHEMICAL    NOTATION. 

These  numbers  do,  in  fact,  represent  the  supposed  relative 
weights  of  atoms.  Different  views  may  be  entertained  of  the 
atomic  constitution  of  bodies ;  and,  in  the  present  state  of 
chemical  knowledge,  the  determinations  of  the  atomic  weight  of 
a  body  from  different  points  of  view  may  not  always  agree :  the 
specific  heat,  for  example,  sometimes  leading  to  one  conclusion, 
the  vapour-density  to  another ;  but  the  idea  of  atoms  and  of 
their  relative  weights,  and  of  the  building  up  of  compounds 
by  the  juxta-position  of  elementary  atoms,  is  perfectly  definite, 
and  affords  the  only  satisfactory  explanation  yet  given  of  the 
observed  laws  of  chemical  combination  (I.  135). 


GERHARDTS   UNITARY    SYSTEM. 

There  are  three  systems  of  atomic  weight  in  use  among 
chemists: — 1.  The  system  adopted  in  this  work,  which  is  the 
same  as  that  in  Gmelin's  Hand-book.  In  this  system,  water 
is  represented  by  the  formula  HO,  and  the  metallic  oxides 
(protoxides)  most  resembling  it  by  the  formula  MO.  The 
atomic  weights  correspond,  for  the  most  part,  with  the  equi- 
valents, substitution  being  supposed  to  take  place,  atom  for 
atom. 

2.  The  system  of  Berzelius,  based  upon  the  hypothesis 
that  all  elementary  gases  contain  equal  numbers  of  atoms  in 
equal  volumes,  so  that  the  atomic  constitution  of  a  compound 
corresponds  with  its  constitution  by  volume.  Thus,  water 
being  composed  of  2  vol.  H  to  1  vol.  O,  is  HgO  ;  hydrochloric 
acid,  being  composed  of  equal  volumes  of  chlorine  and  hydro- 
gen, is  HCl,  &c.  The  atomic  weights  in  this  system  are  the 
same  as  those  in  the  former  (I.  108),  excepting  those  of 
hydrogen,  nitrogen,  phosphorus,  chlorine,  bromine,  iodine, 
and  fluorine,  which  have  half  the  values  there  assigned  to 
them,  viz. :  —  (O  =  8) ;  H  =  0-5  ;  N  =  7  ;  P  =  16-01  ; 
CI  =  17-75;    I  =  63-18;    Br  =  40;    F  =  9*35.     Metallic 


gerhardt's  unitary  system.  513 

protoxides  are  represented  by  the  formula  MO :  e.  g,  potash 
=  KO  ;  black  oxide   of  copper  =  CuO, 

3.  The  system  of  Gerhardt,  based,  like  that  of  Berzelius,  on 
the  hypothesis  that  all  simple  gases  contain  equal  numbers  of 
atoms  in  equal  volumes,  but  carrying  out  that  system  more 
consistently.  The  formula  of  water  in  Gerhardt's  system  is 
HgO,  as  in  that  of  Berzelius.  Moreover,  as  the  vapour-density 
of  mercury  is  to  that  of  oxygen  as  6976  :  1106  (I.  149),  and 
mercuric  oxide  contains  8  parts  by  weight  of  oxygen  to  100 
parts  of  mercury,  it  follows  that  the  proportions  by  volume 
of  mercury-vapour  and  oxygen  which  compose  this  oxide 
must  be  2  vol.  mercury  to  1  vol.  oxygen  :  for  2  x  6976  :  1106 
=  100  :  8  (nearly).  Hence  mercuric  oxide  is  HggO  ;  and 
from  the  analogy  of  cupric  oxide,  ferrous  oxide,  potash,  soda, 
&c.,  with  mercuric  oxide,  it  follows  that  these  oxides  must  be 
CugO,  FcgO,  KgO,  NagO,  &c. ;  or,  generally,  the  formula 
of  a  protoxide  is  MgO,  analogous  to  that  of  water,  HgO. 

If  O  =  8,  the  atomic  weights  of  sulphur,  selenium,  tel- 
lurium, and  carbon  are  the  same  in  Gerhardt's  system  as  in 
that  adopted  in  the  present  work,  but  those  of  all  the  other 
elements  have  only  half  the  usual  values:  —  H  =  0-5,  CI 
=  17 '75,  K  =  19  5,  &c.  Or,  what  is  more  convenient, 
assuming  PI  =  1,  the  atomic  weights  of  O,  S,  Se,  Te,  and  C 
will  be  doubled,  while  those  of  all  the  other  elements  will 
remain  the  same.* 

In  the  following  explanations  and  applications  of  Gerhardt's 
system,  these  double  atomic  weights  of  oxygen,  &c.,  will, 
to  avoid  confusion,  be  denoted  by  letters  with  bars  through 
the  middle  :  thus,  O  =  16,  -S  =  32,  €•  =  12. 

The  following  table  presents  a  comparative  view   of  the 


*  Gmelin,  in  his  Handbook  (Translation,  vol.  vii.  p.  27),  objects  to  Gerhardt's 
atomic  weights,  that  they  do  not  correspond  with  the  equivalent  numbers ;  but 
this,  as  already  shown  (p.  510),  must  necessarily  be  the  case  with  all  systems  of 
atomic  weights  or  combining  numbers,  inasmuch  as  a  body  may  have  several 
equivalents,  but  can  have  only  one  atomic  weight. 


514 


CHEMICAL   NOTATION. 


formulao  of  some  of  the  most  important  chemical  compounds 
in  the  ordinary  notation,  and  in  that  of  Gerhardt. 


Ordinary  System. 

Gerliardt's  System. 

Water 

HO 

H,f> 

Peroxide  of  hydrogen 

H0„ 

HO 

Hydrosulphuric  acid 

HS 

H28 

Sulphuric  acid  (anhydrous) 

SO, 

Htfj 

„     (hydrated) 

.     /   . 

SHO, 

KH,e, 

Hydrochloric  acid    . 

HCl 

HCl 

Hypochlorous  acid  (anhydrous 

CIO 

9»^ 

„     (hydrated) 

C1H0» 

CIHO 

Carbonic  oxide 

CO 

•ee 

Carbonic  acid  (anhydrous) 

co„ 

€f>a 

Nitric  acid  (anhydrous)    . 

NO, 

xM* 

„        „     (hydrated)      . 

NHOg 

NHOa 

Phosphoric  acid  (anhydrous) 

PO, 

P,e. 

„            „    (hydrated) 

PH3O, 

^M* 

Protoxides  (anhydrous)    . 

MO 

M^e 

„  .        (hydrated)      . 

r       MHO,       "l 
t   or  MO. HO   J 

MHO 

Sesquioxides  (anhydrous) 

M,0, 

M,03 

Sulphate  of  potash  (neutral) 

SKO^ 

SK,tt, 

„       (acid) 

s,Kno« 

■SKHO, 

Nitrate  of  potash 

NKO« 

J^^^^.. 

Alum  (anhydrous)   . 

S.KAl^O.o 

-&,KALe8 

Hydrocyanic  acid     . 

C,NH 

eNH 

Cyanic  acid 

C,NIIOa 

eNH-O 

Cyanate  of  soda 

CjNNaOj 

€NNaO 

Hydrosulphocyanic  acid  . 

CsNHS, 

eNLis  , 

Siilphocyanidc  of  silver     . 

C^NAgS, 

-GNAg* 

Alcohol 

C,H,0, 

0,11,0 

Ether       

C,H,0 

^.H.oO 

Acetic  acid  (hydrated)     . 

cji.o, 

€,H,4>, 

„     (anhydrous)  . 

C4H3O3 

eji.e. 

Benzoic  acid  (hydrated)   . 

CuHeO, 

€,H,0, 

„          „     (anhydrous) 

C.,H,03 

Ou".o^3 

Benzoate  of  potash    . 

C.,H,K0, 

■e^H^KOa 
4,H,0, 

Oxalic  acid 

C,H,0« 

These  two  systems  of  notation  possess  in  common  tlie 
advantage  of  representing  the  metallic  protoxides  by  formulae 
analogous  to  that  of  water,  whereas  in  the  system  of  Ber- 
zelius,  this  analogy  is  lost,  water  being  represented  by  Hg-Q, 
and  the  protoxides  of  the  metals  by  MO.  But  the  repre- 
sentation of  water  by  HHO,  as  in  Gerliardt's  system,  pos- 
sesses the  additional  advantage   of  corresponding  with  the 


515 

important  fact,  that  it  is  possible  to  replace  either  the  half  or 
the  whole  of  the  hydrogen  in  water  by  a  metal.  Thus 
potassium  thrown  into  water  displaces  half  the  hydrogen,  and 
forms  hydrate  of  potash,  HKO ;  and  when  this  compound,  in 
the  solid  state,  is  heated  with  an  additional  quantity  of  potas- 
sium, the  remaining  half  of  the  hydrogen  is  displaced,  and  an- 
hydrous potash,  KKO,  is  formed.  On  the  contrary,  when 
potassium  acts  on  hydrochloric  acid,  HCl,  it  displaces  the 
whole  of  the  hydrogen,  and  forms  chloride  of  potassium 
KCl.  This  is  an  important  difference,  which  is  easily  under- 
stood on  the  supposition  that  water  contains  two  atoms  and 
hydrochloric  acid  only  one  atom  of  hydrogen ;  whereas, 
if  these  two  compounds  are  represented  by  the  analogous 
formulas  HO  and  HCl,  the  cause  of  the  difference  of  action 
is  by  no  means  apparent. 

Assuming  as  the  unit  of  vapour- volume  the  space  occupied 
by  1  gramme  of  hydrogen  (or  by  16  grammes  of  oxygen,  14  of 
nitrogen,  35*5  of  chlorine,  &c.),  and  calculating  by  formulae 
analogous  to  those  in  the  third  column  of  the  preceding  table, 
the  weights  of  the  compound  atoms  or  molecules  of  those  com- 
pounds which  are  capable  of  assuming  the  gaseous  form,  it  will 
be  found  that  they  correspond  to  2  volumes  of  vapour.  Thus, 
for  hydrochloric  acid:  H  +  Cl  =  1  +35*5  =  36*5;  and  as  the 
density  of  hydrochloric  acid  gas  is  18*25  times  that  of  hy- 
drogen (see  Table  I.  p.  150.),  it  follows,  that  the  number  36*5 
represents  the  weight  of  2  volumes  of  vapour.  Similarly,  for 
water:  H20=  2  +  16  =  18, which  is  also  the  weight  of  2  volumes 
of  vapour,  the  specific  gravity  of  aqueous  vapour  compared 
with  hydrogen  as  the  unit  being  9.  Alcohol  =  -G2HgO= 24  +  6 
+ 16=46  :  and  the  specific  gravity  of  alcohol  vapour  (H=  1) 
is  23.  Ether=-G4Hioa=48  + 10  + 16  =  74,  which  is  twice  37, 
the  weight  of  a  unit- volume  of  ether- vapour. 

In  the  formula?  of  the  second  column,  this  uniformity  of 
vapour-volume  is  not  observed.  Some  of  them,  as  those  of 
water  HO,  ether  C^HgO,  anhydrous  acetic  acid  C4II3O3,  and 


516  CHEMICAL   NOTATION. 

lijdrated  sulphuric  acid  SHO^,  represent  1  volume  of  vapour, 
when  referred  to  the  unit  above-mentioned,  viz.  the  space  occu- 
pied by  1  gramme  of  hydrogen,  or  2  volumes,  if  compared  with 
the  volume  of  half  a  gramme  of  hydrogen,  or  8  grammes  of 
oxygen;  while  the  rest,  for  example,  hydrochloric  acid,  HCl, 
and  hydrated  acetic  acid,  C^H^O^,  represent  2  volumes 
or  4  volumes  of  vapour,  according  to  the  unit  adopted.  (See 
the  table  in  Vol.  L,  pp.  149-155.)  To  bring  all  these  for- 
mulae to  the  same  standard  of  vapour- volume,  it  is  necessary, 
therefore,  to  double  those  first  mentioned,  thus :  water  =  HgO^ ; 
ether,  C8H,o02 ;  anhydrous  acetic  acid,  CgHgOg ;  hydrated 
sulphuric  acid,  SgHgOg,  &c. ;  and  if  the  corresponding  change 
be  made  in  the  formulae  of  the  analogous  compounds,  which 
are  not  known  to  exist  in  the  gaseous  state,  e.  g.  anhydrous 
metallic  protoxides,  MgOg*,  neutral  sulphate  of  potash,  S2K2O8, 
&c.,  it  will  be  found  that  Gerhardt's  formulae  may,  in  all  cases, 
be  converted  into  those  of  the  ordinary  notation,  by  doubling 
the  number  of  atoms  of  carbon,  oxygen,  sulphur,  selenium, 
and  tellurium.* 

There  is  yet  one  class  of  bodies  whose  atomic  weights  repre- 
sent, not  two,  but  one  volume  of  vapour,  viz.  the  elementary 
bodies.  To  reduce  these  bodies  to  the  same  standard,  it  is 
necessary  to  assume  that  each  molecule  of  an  elementary  body 
in  the  free  state  consists  of  two  elementary  atoms,  e.  g.  hy- 
drogen, HH ;  chlorine,  ClCl. 

This  hypothesis  is  justified  by  numerous  considerations. 
First:  It  accords  with  the  polar  view  of  the  constitution  of 
bodies  suggested  by  the  phenomena  of  electrolysis  (I.  238). 
Secondly:  It  is  justified  by  certain  relations  of  boiling  point 

*  Gerhardt  applied  the  term  unitary  to  his  system  of  notation,  because  it  is 
based  on  the  reduction  of  all  formulae  to  one  common  standard,  the  formulaj 
being  derived  one  from  the  other  by  substitution.  The  ordinary  system,  being 
founded  rather  on  the  formation  of  compounds  in  successive  binary  groups 
(c.  g.  potash  =  KO  ;  sulphuric  acid  =  SO3 ;  sulphate  of  potash  =  KG .  SO3),  is 
called  the  Dualistic  system. 


erhardt's  unitary  system.  517 

and  vapour-density,  to  be  considered  hereafter.  Thirdly: 
There  are  numerous  instances  of  chemical  action  in  which  two 
atoms  of  an  elementary  body  unite  together  at  the  moment  of 
chemical  change,  just  like  heterogeneous  atoms.  Thus,  when 
the  hydride  of  copper,  CU2H,  is  decomposed  by  hydrochloric 
acid,  cuprous  chloride  is  formed,  and  a  quantity  of  hydrogen 
evolved  equal  to  twice  that  which  is  contained  in  the  hydride 
itself: — 

Cu^H  +  HCl  =  Cu^Cl  +  HH. 

This  action  is  analogous  to  that  of  hydrochloric  acid  on  cuprous 
oxide : — 

Cu,0  +  2HC1  =  2CU2CI  +  H^a. 

In  the  latter  case,  the  hydrogen  separated  from  the  hydro- 
chloric acid  unites  with  oxygen ;  in  the  former,  with  hydrogen. 
When  solutions  of  sulphurous  and  hydrosulphuric  acids  are 
mixed,  the  whole  of  the  sulphur  is  precipitated: — 

SOa  +  2H2S  =  2H2a  +  S.  S2, 

the  action  being  similar  to  that  of  sulphurous  acid  on  hydro- 
selenic  acid : — 

SO2  +  2H2^  =  2U^Q  +  S .  Se^. 

In  the  one  case,  a  sulphide  of  selenium  is  formed;  in  the 
other,  a  sulphide  of  sulphur.  The  precipitation  of  iodine  which 
takes  place  on  mixing  hydriodic  with  iodic  acid,  affords  a 
similar  instance  of  the  combination  of  homogeneous  atoms. 
The  reduction  of  certain  metallic  oxides  by  peroxide  of  hy- 
drogen, is  another  striking  example  of  this  kind  of  action. 
When  oxide  of  silver  is  thrown  into  this  liquid,  water  is  formed ; 
the  silver  is  reduced  to  the  metallic  state ;  and  a  quantity  of 
oxygen  is  evolved  equal  to  twice  that  which  is  contained  in 
the  oxide  of  silver.  It  appears,  indeed,  as  if  atoms  could  not 
exist  in  a  state  of  isolation.     An  atom  of  an  elementary  body 

VOL.  II.  O  O 


518 


CHEMICAL   NOTATIOJf. 


must  unite,  either  with  an  atom  of  another  element,  or  witli  one 
of  its  own  kind. 

The  same  tendency  of  homogeneous  atoms  to  combine 
together  is  exhibited  by  certain  groups  of  atoms  called  com- 
pound radicals,  which  behave  in  most  respects  like  elementary 
substances,  and  pass  as  entire  groups  from  one  state  of  com- 
bination to  another.  Thus  there  is  a  series  of  hydrocarbons 
called  the  alcohol-radicals  (p.  531),  e.g.  methyl,  ^^Hg ;  ethyl, 
^2^5,  which  may  be  regarded  as  compound  metals,  capable 
of  taking  the  place  of  hydrogen  in  combination  with  chlorine, 
iodine,  oxygen,  &c.,  just  as  simple  metals  do.  Now  when 
zinc-ethyl,  ^^^HaZn,  and  iodide  of  methyl,  ^^Ilgl,  are  heated 
together,  double  decomposition  takes  place,  the  products 
being  iodide  of  zinc,  and  methyl- ethyl : — 

C,H,.Zn  +  CH,I  =  Znl  +  (4:,H,) .  (GH,). 

And  when  zinc-ethyl  is  heated  with  iodide  of  ethyl,  a  similar 
action  takes  place,  but  attended  with  formation  of  free  ethyl :  — 

C,H..Zn  +  e.HJ  =:  Znl  +  (<;,H,) .  (e,H,). 

Moreover,  the  boiling  points  and  vapour-densities  of  these 
radicals  are  related  to  each  other  and  to  those  of  the  com- 
pound radicals,  methyl-ethyl,  butyl-amyl,  &c.,  in  a  manner 
which  can  only  be  explained  by  supposing  the  radicals  in  the 
free  state  to  consist  of  double  atoms.  This  will  be  seen  from 
the  following  Table ; — 


Sp.  gr.  at  ( P  C. 

Vapour-density. 

Boiling-point. 

Ethyl-butyl    . 

e,H, 

.  0,H, 

0-7011 

3053 

62°  C. 

Ethyl- amy  1     . 

^H, 

.  ^.H„ 

0-7069 

3522 

88 

Butyl 

<^.H, 

•    ^4H9 

0-7057 

4070 

106 

Butyl-amyl     . 

^.H, 

.  <^sH„ 

0-7247 

4-465 

132 

Amyl      . 

^.H„ 

•  ^.H, 

0-7413 

4-956 

158 

Butyl-caproyl 

4i,U, 

.  ^«H„ 

? 

4-917 

155 

Caproyl  . 

<^6U,3 

.  0,H.3 

0-7564 

5-983 

202 

gerhardt's  unitary  system.  519 

The  regular  gradation  of  these  densities  and  boiling  points 
plainly  shows  that  the  proper  places  of  butyl,  amyl,  and 
caproyi  in  the  series,  are  those  which  they  occupy  in  the 
table,  and  consequently  that  their  atomic  weights  in  the  free 
state  are  double  of  those  which  appertain  to  them  in  com- 
bination: e.g.,  amyl  in  combination  =  ^-^n  =  71;  free 
amjl  =  (C,H„),  =  142. 

Fourthly :  Elementary  bodies  frequently  act  upon  others 
as  if  their  atoms  were  associated  in  binary  groups.  Thus 
chlorine  acting  upon  potash  forms  two  compounds,  chloride  of 
potassium  and  hypochlorite  of  potash : — 

KKa  +  ClCl  =  CIK  +  CIKO; 

just  as  chloride  of  cj'anogen  would  form  chloride  of  potas- 
sium and  cyanate  of  potash.  The  quantity  of  chlorine  which 
acts  upon  an  atom  of  potash,  is  not  1  at.  =  35 '5,  but 
2  at.  =  70.  Similarly,  when  metallic  sulphides  oxidise  in 
the  air,  both  the  metal  and  the  sulphur  enter  into  combina- 
tion with  oxygen.  Sulphur  acting  upon  potash  forms  a 
sulphide  and  a  hyposulphite.  Lastly,  when  zinc-ethyl  is 
exposed  to  the  action  of  chlorine,  iodine,  &c.,  these  elements 
unite  separately  with  the  zinc  and  with  the  ethyl,  thus : — 

Qr^H.Zn  +  ClCl  =  ^^H.Cl  +  ZnCL 

Double  Decomposition  regarded  as  the  Type  of  Chemical  Action 
in  general. — Double  decomposition  is  generally  understood  as 
an  action  taking  place  between  four  elements  or  groups  of 
elements ;  but  since  it  appears  that  homogeneous  atoms  may 
exhibit  towards  one  another  the  same  chemical  relations  as 
atoms  of  different  bodies,  it  follows  that  the  same  kind  of 
action  may  be  supposed  to  take  place  when  less  than  four 
bodies  are  concerned.  The  extension  of  this  view  of  chemical 
action  to  cases  in  which  three  elements  or  groups  of  elements 
come  into  play,  is  sufficiently  illustrated  by  the  examples 
just  given.     But  w^e  may  proceed  still  further  in  the  same 

o  o  2 


520  CHEMICAL   NOTATION. 

direction,  and  regard  as  double  decompositions  those  reactions 
which  are  commonly  viewed  as  the  simple  combination  or 
separation  of  two  elements,  or  as  the  substitution  of  one  ele- 
ment for  another.  Thus,  when  potassium  burns  in  chlorine 
gas,  the  reaction  may  be  supposed  to  take  place  between  two 
atoms  of  chlorine  and  two  atoms  of  potassium: — 

KK  +  ClCl  =  KCl  +  KCl. 

Again,  the  decomposition  of  cyanide  of  mercury  by  heat  may 
be  represented  thus: — 

CyHg.  CyHg  =  CyCy  +  Hgllg. 

The  simple  replacement  of  one  element  by  another  may  also 
be  regarded  as  a  double  decomposition,  by  supposing  the  for- 
mation of  an  intermediate  compound  to  take  place.  Thus, 
the  action  of  zinc  upon  hydrochloric  acid  may  be  supposed 
to  consist  of  two  stages :  — 

ZnZn  +  HCl  =  ZnH  +  ZnCl, 
and  ZnH    +  HCl  =  ZnCl  +  HH. 

It  is  true  that  the  formation  of  the  intermediate  compound, 
the  hydride  of  zinc,  cannot  be  actually  demonstrated  in  this 
case,  because  it  is  decomposed  as  fast  as  it  is  formed ;  but  in 
other  cases  the  two  stages  of  the  action  can  be  distinctly 
traced.  Thus,  it  is  well  known  that  hydrochloric  acid  does 
not  dissolve  copper ;  but  an  alloy  of  zinc  and  copper,  CugZn, 
dissolves  in  it  readily,  with  evolution  of  hydrogen.  Here  it 
may  be  supposed  that  the  first  products  are  chloride  of  zinc 
and  hydride  of  copper,  a  known  compound  : — 

Cu^Zn  +  HCl  =  Cu^H  +  ZnCl; 

and  that  the  hydride  is  afterwards  acted  upon  by  the  acid 
in  the  manner  already  explained.  Again,  when  zinc  and 
iodide  of  ethyl  are  heated  together  in  a  sealed  tube,  iodide  of 
zinc  and  zinc-ethyl  are  obtained,  thus: — 

ZnZn  4-  (^2^5).  I  =  Znl  +  Zn  (^^JIJ; 


TYPES  AND   RADICALS.  521 

and  the  zinc-ethyl,  when  heated  with  excess   of  iodide   of 
ethjl,  yields  iodide  of  zinc  and  free  ethyl :  — 

Zn  (G,H,)  +  (C,HJ.  I  =  Znl  +  (e,H,)  (C,H,). 

In  this  manner,  all  chemical  reactions  may  be  reduced  to 
one  type,  viz.,  a  mutual  interchange  of  atoms  between  two 
binary  groups. 


TYPES  AND  RADICALS. — RATIONAL  FORMULA. 

The  rational  formula  of  a  compound  is  inferred  from  its 
modes  of  formation  and  decomposition.  When  cyanide  of 
sodium  is  mixed  with  nitrate  of  silver,  an  interchange  of 
elements  takes  place,  resulting  in  the  formation  of  nitrate  of 
soda  and  cyanide  of  silver  :  — 

^N.  Na  +  NO3.  Ag  =  ^N .  Ag  +  NOg.Na. 

Here  the  group,  or  radical  NO3  passes  from  the  silver  to  the 
sodium,  and  in  a  similar  manner  it  may  be  transferred  to 
potassium,  barium,  copper,  &c.  Hence  it  may  be  inferred 
that  the  nitrates  consist  of  NO3  associated  with  a  metal. 
Similarly,  -GN  may  be  regarded  as  the  radical  of  the  cyanides; 
■SO^  of  the  sulphates,  &c.  When  alcohol,  -GgHgO,  is  treated 
with  potassium,  one-sixth  of  the  hydrogen  is  evolved,  and  the 
compound  Q^H^KQ^  is  formed.  Again, — alcohol  treated  with 
chloride,  bromide,  and  iodide  of  phosphorus,  yields  the  com- 
pounds, •G2H5CI,  Q,fifir,  and  -G-gH^I  ;  and  when  the  com- 
pound -G-gngKO  is  treated  with  -GgHgT,  iodide  of  potassium 
and  ether  are  formed :  — 

G,HJ  +  •^»5'}0  =  KI  +  g^H^jO. 

From  these  and  other  reactions,  alcohol  and  its  derivatives 
are  supposed  to  contain  the  radical  ethyl,  -GgHg,  alcohol  being 

o  o  3 


522  TYPES   AND   RADICALS. 

its  liydrated  oxide,     ^tt^J^j  analogous  to  hydrate  of  potash, 
XT  JO,  and  ether  its  anhydrous  oxide,   jQ^tt']  O,  analogous 

It  must  be  especially  observed,  however,  that  the  reason 
for  admitting  the  existence  of  ethyl  as  a  radical  in  the  alcohol 
compounds,  is  that  this  supposition  affords  the  readiest  ex- 
planation of  certain  reactions.  Other  reactions  may  point  to 
a  different  conclusion.  Thus,  since  alcohol  heated  to  a  high 
temperature  with  strong  sulphuric  acid  is  resolved  into 
defiant  gas  and  water,  it  may  be  regarded  as  a  hydrate  of 
defiant  gas,  Ojll^ .  IlgO.  Again, —  certain  sulphates,  when 
heated  to  redness,  give  off  anhydrous  sulphuric  acid;  and 
sul})hatc  of  baryta  may  be  formed  by  the  direct  combination 
of  the  same  anhydrous  acid  with  anhydrous  baryta.  Such 
reactions  might  lead  to  the  conclusion  that  oxygen-salts  are 
compounds  of  anhydrous  metallic  oxides  with  anhydrous 
acids,  rather  than  of  metals  with  salt- radicals,  which  is,  in 
fact,  the  ordinary  view.  Similarly,  ammoniacal  salts  are  re- 
garded as  compounds  of  NHg  with  hyd rated  acids,  or  of  NH^ 
with  acid  radicals,  according  to  the  reactions  specially  under 
consideration. 

It  appears,  then,  that  the  same  compound  may  have  several 
rational  formulae.  This  of  course  implies  that  the  formula  is 
an  expression,  not  of  the  constitution  of  the  body  in  a  state  of 
rest,  but  of  the  manner  in  which  the  atoms  are  supposed  to 
arrange  themselves  when  subjected  to  certain  influences. 
It  is  no  longer  the  question  what  the  absolute  constitution  of 
a  substance  may  be,  but  of  how  many  forms  of  constitution 
the  substance  fulfils  the  conditions.  For  in  chemical  sub- 
stances, as  in  the  objects  of  a  branch  of  natural  history,  any 
one  individual  exhibits  more  or  less  distinctly  the  features  of 
every  other. 

The  greater  the  number  of  elementary  atoms  entering  into 


TYPES   AND   RADICALS.  523 

tlie  constitution  of  a  compound,  the  more  numerous  will  be 
the  possible  arrangements  of  those  atoms,  and  the  greater, 
therefore,  the  number  of  rational  formulae  which  may  be 
assigned  to  the  compound.  Practically,  however,  it  is  found 
that  a  small  number  of  rational  formulae — seldom  more  than 
two  or  three  —  suffices  for  each  compound ;  and  moreover,  - 
that  the  formulae  of  all  bodies  whatever  may  be  reduced  to  a 
small  number  of  general  types.  Of  these,  Gerhardt  adopts 
four,  viz. :  — 

Water,  tt]  ^>  from  which  are  derived  the  oxides,  sulphides, 

selenides,  and  tellurides. 

Hydrochloric  acid,  HCl,  the  type  of  the  chlorides,  bromides, 
iodides,  fluorides,  and  cyanides. 

Ammonia,  N]H,   the   type   of   the   nitrides,   phosphides, 
^H 
arsenides,  &c. 

Hydrogen,  HH,  the  tj'-pe  of  the  elementary  bodies,  com- 
pound radicals,  hydrides  of  metals  and  radicals,  &c. 

These  typical  formulae  all  correspond  to  2  volumes  of 
vapour. 

The  formulae  of  the  several  compounds  included  under  each 
of  these  types  are  obtained  by  replacing  one  or  more  of  the  ele- 
mentary atoms  contained  in  them  by  another  radical,  simple 
or  compound.  The  derivative  compound  is  called  primary, 
secondary,  or  tertiary,  according  to  the  number  of  atoms  of 
hydrogen  in  the  type  which  are  thus  replaced.  For  example, 
the  hydrated  metallic  oxides,  which  are  formed  from  the  type 
water  by  the  substitution  of  1  at.  of  a  metal  for  1  at.  hydrogen, 

are  primary  oxides ;  e.  ^.  hydrate  of  potash,   t^]0;    the   an- 
hydrous oxides,  in  which  both  atoms  of  hydrogen  arc  similarly 

o  o  4 


524  TYPES   AND   RADICALS. 

replaced,  as  in  anhydrous  potash,  tt-JO,  are  secondary  oxides. 

The  replacement  of  1  at.  H  in  ammonia  by  ethyl,  "CgHg,  forms 
a  primary  nitride,  viz.,  ethylamine,  N(-G^H5)n2 ;  similarly, 
biethylamine,  N(-G2H5)2H,  is  a  secondary  nitride;  and  tri- 
cthylamine,  N  (02115)3,  a  tertiary  nitride. 

Equivalent  Values  of  Radicals.  —  A  radical  is  monatomic, 
hiatomicy  triatomicy  &c.,  according  as  its  atom  or  molecule  is 
equivalent  to  one,  two,  three,  &c.,  atoms  of  hydrogen.  Potas- 
sium and  ethyl  arc  monatomic  radicals.  Sulphuryl,  -SOg,  is  a 
biatomic  radical,  and  by  replacing  2  at.  H  in  two  molecules 

TT  Sill 

of  water,  tt^]^2'  forii^s  hydrated  sulphuric  acid,  ti^]^' 
Fhosplioryl,  PO,  is  a  triatomic    radical,    and   by   replacing 

TT 

3  atoms  of  hydrogen  in  three  molecules  of  water,  TT^jOg,  forms 

the  ordinary  hydrate  of  phosphoric  acid,  PH3O4  =   tt  jOg. 

When  a  metal  forms  two  classes  of  salts,  its  atom  has  a 

different  equivalent  value  in  each.      Thus,  in  the  platinous 

compounds,  Pt  (=  98)  is  monatomic  ;  in  the  platinic  salts,  it 

CI 
is  biatomic:  thus,  platinic  chloride  =  Pt  {p,.    In  the  ferrous 

compounds,  Fe  (=  28)  is  monatomic;  in  the  ferric  com- 
pounds, it  is  sesquiatomic,  Fe2  being  equivalent  to  H3,  or 

TT 

Fe-|  to  H:  thus,  ferric  oxide  =  ^  ^jOg.      In   the   mercuric 

compounds,  Hg(  =  100)  is  monatomic;  in  the  mercurous 
compounds,  it  is  semi-atomic;  the  double  atom,  Hg2(=  200), 
being  the  equivalent  of  1  atom  of  hydrogen.  In  arsenious 
acid,  ASgOg,  which  is  derived  from  3  molecules  of  water, 
Asg  is  equivalent  to  Hg,  and  therefore  As  to  II3;  but  in 
arsenic  acid,  AsgOg,  derived  from  5  molecules  of  water.  As  is 
equivalent  to  H^.* 

*  If  the  notion  of  equivalents  be  strictly  adhered  to,  independently  of  the 
atomic  theory,  the  formuloe  of  bisalts  and  scsquisalts  may  be  dispensed  with, 


TYPES   AND   RADICAL S.  525 

Since  a  compound  may  have  several  rational  formulae,  or, 
in  other  words,  maj  be  represented  as  containing  different 
radicals,  it  is  necessary  to  determine  the  relation  which  exists 
between  the  equivalents  of  such  radicals.  This  relation  is 
determined  by  the  following  general  law :  —  Every  equivalent  of 
hydrogcji  added  to  a  radical  diminishes  by  unity  the  equivalent 
value  of  the  entire  radical;  and  every  equivalent  of  hydrogen  sub- 
tracted from  a  radical  increases  by  unity  the  total  equivalent 
value  of  the  entire  radical.  Thus,  nitric  acid  may  be  represented 
by  the  three  following  formula : — 

In  the  first  of  these  formulae,  which  represents  nitric  acid  as 
formed  from  one  molecule  of  water,  HgO,  the  radical  nitryl, 
ISTOg,  is  equivalent  to  1  atom  of  hydrogen;  in  the  second,  which 
is  formed  from  2  molecules  of  water,  H^O^,  the  radical  azotyl, 
NO,  formed  from  nitryl  by  abstraction  of  O,  the  equivalent  of 
Hg,  takes  the  place  of  3  atoms  of  hydrogen  ;  and  in  the  third, 
which  is  formed  from  3  molecules  of  water,  HgOg,  the  radical 
nitricum,  N,  formed  from  nitryl  by  abstraction  of  Oo,  the 
equivalent  of  H^,  takes  the  place  of  5  atoms  of  hydrogen. 

Again,  uranic  oxide  may  be  represented  either  as    tt^JOs, 

and  the  different  classes  of  salts  of  the  same  metal  regarded  as  containing 
different  radicals :  thus  the  mercurous  salts  may  be  regarded  as  salts  of 
viercuroswn,  Hg=200  ;  the  mercuric  salts  as  containing  mercuricum,  hg  =  lOO  : 
thus  — 

Mercurous  chloride  or  chloride  of  mercurosum  .  .  HgCl  =  200  4  35'5 
Mercuric  chloride  or  chloride  of  mercuricum  .  .  .  hgCl=100+35-5 
Ecrrous  chloride  or  chloride  of  ferrosum  ....  FeCl  =  28  +35-5 
Ferric  chloride  or  chloride  of  ferricum      ....     feCl    =   185  +  35-5 

This  mode  of  representation  might  be  made  consistent  with  the  atomic 
theory,  by  supposing  that  the  ultimate  atom  of  iron  weighs  9^ ;  that  a  double 
atom  of  iron  constitutes  ferricum  =  18§ ;  and  a  triple  atom,  ferrosum,  =  28  : 
similarly,  the  atom  of  mercury  weighing  100,  a  double  atom  constitutes  mer- 
curosum. In  organic  compounds,  such  relations  between  radicals  are  actually 
observed  :  thus,  ethylene,  G2II4,  =  2  x  GHj ;  propylene,  C.II^,  =  3  x  Gllj  ;  buty- 
Icuc,  G^Hg  =  4  X  OII2,  &c. 


526  TYPES   AND   RADICALS. 

or  as  TT^riJ^'     The  first  of  these  formulae  represents  three 

molecules  of  water,  HgOa,  and  contains  the  radical  Ug  =  H3 ; 
the  second  represents  one  molecule  of  water,  and  contains  the 
radical  ui^anyl,  U2O,  equivalent  to  H;  and  accordingly,  Ug — O, 
is  equivalent  to  Hg  —  Hg  =  H.  Another  example  of  the 
general  law  above  stated  is  afforded  by  the  radicals  of  the 
monatomic,  biatomic,  and  triatomic  alcohols  (p.  531). 

Conjugate  Radicals.  —  Ax\j  compound  radical  may  be  regarded 
as  a  compound  of  two  or  more  simpler  radicals.  Thus,  ethyl, 
•G2H5,  may  be  represented  as  CHg  +  CH3,  or  as  -GgHg  +  Hg ; 
acetyl,  -GgHgO,  the  radical  of  acetic  acid,  may  be  regarded  as 
.GO+'GH3,  or  as  -G^Hg  -j-  O,  &c.  Radicals  viewed  in  this 
manner  are  said  to  be  conjugated.  A  radical  may  be  conjugated 
either  by  addition,  as  in  the  preceding  examples,  or  by  sub- 
stitution of  another  radical  for  one  or  more  atoms  of  hy- 
drogen; e.g.,  from  benzoyl, -GyH^O,  is  formed  nitro-benzoyl, 
G7H4(N02)0,  by  substitution  of  a  molecule  of  nitryl,  NOg,  for 
1  at.  H.  Similarly,  from  acetyl,  -GgHa-Q,  are  formed  mono- 
chloracetyl,  Qji^S^\)Q>,  and  tcrchloracetyl,  Gr^Q\jl^. 

An  important  class  of  conjugate  radicals  consists  of  those 
which  are  formed  of  certain  metals  —  arsenic,  antimony,  tin, 
bismuth,  &c.  —  associated  with  the  alcohol-radicals.  For  ex- 
ample: cacodyl,  or  arsen-bimethyl,  A^{Grl\).-^\  stibethyl, 
Sb(-G2H5)3;  arsenethylium,  As(G2H5)4;  stannethyl,  Sn..G2H5. 
The  same  radicals  may  be  regarded  as  conjugated  by  substi- 
tution :  e.  g.y  arsenethyl,  As(-G2H5)3,  as  formed  from  ammonia, 
NH3,  the  3  at.  H  being  replaced  by  ethyl,  and  tlie  nitrogen  by 
arsenic.  In  like  manner,  arsenethylium,  As(G2H5)4,  may 
be  derived  from  ammonium,  NH^. 

The  equivalent  in  hydrogen  of  a  conjugate  radical  may 
be  determined  by  the  two  following  rules,  deduced  from  the 
general  law  given  at  page  525  : — 

1.  The  equivalent  in  hydrogen  of  a  radical  conjugated  hy 
addition  is  equal  to  the  difference  of  the  equivalents  of  the  con- 


CLASSIFICATION.  527 

stituent  radicals.  Thus,  acetyl  (^3113)0,  which  is  equivalent 
to  H,  is  composed  of  acetosyl,  ^2^3»  ^^*  ^°  ^>  ^^^  ^  ^^* 
to  Hg ;  arsenethyl  As  (■^•2115)3,  which  is  equivalent  to  Hg,  is 
composed  of  As  (arsenicum),  eq.  to  H5*,  and  (^2^^o)3»  ^^' 
to  H3 ;  cacodjl,  As  (^H3)2,  which  is  equivalent  to  H,  is  com- 
posed of  As  (arsenosum),  eq.  to  H3,  and  (•GH3)2  eq.  to  Hg. 

2.  The  equivalent  in  hydrogen  of  a  radical  conjugated  by 
substitution  is  equal  to  the  difference  between  the  sum  of  the 
equivalents  of  the  constituent  radicals  and  the  equivalent  of  the 
hydrogen  replaced.  For  example, —  acetyl  ^2^3'^^  which  is 
equivalent  to  H,  may  be  regarded  as  Q^^d  +  ^  (^9.*  ^^ 
H  +  Hg)  minus  Hg. 


CLASSIFICATION    OF    CHEMICAL    COMPOUNDS. 

Bodies  may  be  classified  in  two  ways.  1.  According  to 
their  origin,  as  when  the  acids,  salts,  oxides,  &c.,  of  copper 
are  made  to  form  one  group ;  those  of  chromium  another, 
those  of  ethyl  a  third,  &c.  2.  According  to  their  chemical 
functions,  independently  of  origin;  the  acids  forming  one 
group,  the  bases  a  second,  the  alcohols  a  third,  the  ethers  a 
fourth,  &c.  The  former  mode  of  classification  is  best  adapted 
to  tlie  detailed  description  of  compounds;  the  latter  forgiving 
a  general  view  of  their  mutual  relations. 

The  following  table  exhibits  Gerhardt's  system  of  clas- 
sification by  types,  or  according  to  chemical  functions  : — 


♦  Oxide  of  arsenethyl  is  As(0^H5)3O  or  As2(C2Hg)g02 ;  now  as  (^Ji^)^  is 
equivalent  to  -O;  this  last  formula  may  be  derived  from  that  of  arsenic  acid, 
AS2O5  or  AS2O3.O2  by  the  substitution  of  (€-2Si^)Q  for  -Gg ;  hence  As  has  in 
oxide  of  arsenethyl  the  same  equivalent  value  that  it  has  in  arsenic  acid  ;  that 
is  to  say,  it  is  equivalent  to  H^,  On  the  other  hand,  oxide  of  cacodyl  is 
As2(-e-H3)4-6-;  which  has  the  same  equivalent  value  as  ASg .  O2O,  or  As^Og, 
which  is  the  formula  of  arsenioas  acid.  Hence  the  radical  As  in  cacodyl  has 
the  same  value  as  in  arsenious  acid,  viz.,  equivalent  to  H^. 


CLASSIFICATION  OF  BODIES  ACCORDING 


WATER   TYPE, 


OXIDES. 


r  Bases  proper. 


Deriva- 
tives 
with 
Positive 
Radicals. 


I.  Primary    or   hydrated 
bases  (hydrate  of  potash 

^■O,    hydrate    of    ar- 


Dcriva-  ' 

tives 

with 
Negative 
Radicals. 


Inter- 
mediate 
Deriva- 
tives. 


senethylium). 
2.  Secondary  or  anhydrous 
bases  (oxide  of  potas- 
sium). 

Aleoliols  or  Hydrocar- 
tourettcd  Bases. 

1.  Primary  or  alcohols 
proper  (vinic  alcohol, 
hydrate  of  phenyl,  gly- 
col, glycerine). 

2.  Secondary  alcohols  or 
ethers  (oxide  of  ethyl). 


Aldehydes. 

1.  Primary  (acetic  alde- 
hyde, bitter  almond  oil). 

2.  Secondary. 

Acids. 

1.  Primary  or  hydrated 
acids  (sulphuric,  acetic, 
cyanic  acids). 

2.  Secondary  or  anhydrous 
acids. 


Oxygen-salts. 

Sulphates,  nitrates,  cyan- 
ates. 


Compound  Ethers. 

Sulphate,  cyanatc,  oxalate 
of  etliyl,  glyceridcs, 
stearin,  &c. 

Compound  Aldehydes. 


SULPHIDES 

(Selenides,  Tellurides). 


Basic  Sulphides. 

1,  Primary  or  hydrosul- 
phates  (hydrosulphate 
of  potassium). 


2.  Secondary  or  metallic 
sulphides  (sulphide  of 
potassium). 

Alcoholic  Sulphides. 

1.  Primary  or  mercaptans 
(hydrosulphate  of  ethyl) 


2  Secondary  or  hydrosul- 
phuric  ethers  (sulphide 
of  ethyl). 

Aldehydic  Sulphides. 

1.  Primary  (sulphobenzol) 

2.  Secondary. 

Acid  Sulphides. 

1.  Primary  (hydrosulpho- 
cyanic  acid). 


2.  Secondary  (sulphide  of 
benzoyl). 


Sulphur-salts. 

Sulphocyanidcs,  sulphan- 
timoniates. 

Compound    Sulpliur- 
ethers. 

Thiacetate  of  ethyl,  sul- 
phocyanide  of  ethyl. 

Compound    Sulphur- 
aldehydes. 


HYDROCHLORIC- 

HCl. 


CHLORIDES 

(Bromides,  Iodides, 

Fluorides). 


Basic  Chlorides. 

Metallic  chlorides  (chlo- 
ride of  potassium). 


Alcoholic  Chlorides. 

Hydrochloric  ethers(ch\o- 
ride  of  ethyl). 


Aldehydic  Chlorides. 

Chloride  of  aldchy  dene. 


Acid  Chlorides. 

Chloride  of  acetyl,  oxy- 
chloride  of  phospho- 
rus, chloride  of  cyan- 
ogen, free  chlorine. 


TO  THEIR  CHEMICAL  FUNCTIONS. 


ACID-TYPE, 


CYANIDES. 


Basic  Cyanides. 

Metallic  cyanides  (cyanide 
of  potassium,  ferrocy- 
anide  of  potassium). 


Alcoholic  Cyanides. 

Hydrocyanic  ethers  or  nitriles 
(acetonitrile,  hydrocyanic 
acid). 


Aldeliydic  Cyanides. 


Acid  Cyanides. 

Cyanide    of    benzoyl,    free 
cyanogen. 


AMMONIA    TYPE, 


H. 


N^  H, 


NITRIDES 

(Phosphides). 


Basic  Nitrides. 

1.  Primary  (amide  of  potas- 
sium). 


2.  Secondary. 

3.  Tertiary  (nitride  of  po- 
tassium). 

Alcoholic  Nitrides. 

1.  Primary  (ethylamine). 


2.  Secondary  (biethylamine). 

3.  Tertiary  (triethylamine). 


Aldehydic  Nitrides. 

1.  Primary. 

2.  Secondary. 

3.  Tertiary. 

Acid  Nitrides. 

1.  Primary  (benzamide,  cy- 
anamide,  succinamide). 


2.  Secondary  (succinimide, 
benzoyl-phenylamide). 

3.  Tertiary  (bibenzoyl-sali- 
cylamide,  boramide,  free 
nitrogen). 

Amido^en -salts. 

Benzamidate  of  mercury. 


Alcalamides. 

Oxanilide,  eth3'lacetamide. 


HYDROGEN    TYPE, 

HH. 


METALS 

(Metalloids). 


Basic  Metals. 

1.  Primary  or  metallic  hydrides 
(hydride  of  copper). 


2.  Secondary  or  metals  proper 
(potassium,  stibethyl,  tctre- 
thylium). 

Alcoholic  Metals. 

L  Primary  or  alcoholic  hydrides 
(marsh-gas,  benzin^. 


2.  Secondary  :  the  so-called 
alcohol-radicals  (ethyl,  amyl, 
phenyl). 

Aldehydic  Metals. 

1.  Primary  or  aldehydic  hy- 
drides (olefiant  gas). 

2.  Secondary. 


Acid  Metals. 

L  Primary  or  acid  hydrides 
(hydride  of  benzoyl,  hydro- 
chloric acid,  hydrocyanic 
acid). 

2.  Secondary  or  metalloids 
(benzoyl,  chlorine,  cyano- 
gen). 


Here  might  be  placed  many 
compounds  already  included  in 
the  preceding  classes  :  e.g.^  the 
cyanides  of  ethyl,  &c.,  contain- 
ing the  radical  of  cyanic  acid 
and  an  alcohol-radical. 


530  CLASSIFICATION. 


WATER-TYPE. 


Positive  Oxides. — A,  Bases  proper,  or  Metallic  Oxides. — 
These  compounds  are  formed  by  the  substitution  of  a  metallic 
radical,  simple  or  compound,  for  the  hydrogen,  in  one,  two, 
or  three  molecules  of  water: — 

oi,  Monatomic. — Hydrate  of  potash,  tt]0;  anhydrous  pot- 
ash or  oxide  of  potassium,  t^]0; — cupric  hydrate,  ttJO; — 
cupric  oxide,  p   ]0; — hydrate  of  ammonium,     tt'*]0; — 

hydrate  of  tetramercurammonium,     tt'^'*]  O  ;  —  hydrate    of 
tetrethylium,-^<^^^5  )4]0;— oxide  of  cacody l,^^g^,'^^3)2 1^.__ 

oxide  of  arsenethylium,   a   //^^tt^\?0. 

/3.  Biatomic. —  Platinic  hydrate,  tt  jOg;  platinic  oxide, 
^JjO^  ;  oxide  of  stibethyl,  Itjc^J' i'^^^** 

y.  Triatomic.  —  Hydrate  of  alumina,  tt  ^]  ^3  ;  anhydrous 
alumina,    *  1*  j  O3 ;  antimonic  hydrate,  tt  ]  O3  ;     antimonic 

oxide,  mlOg;  teroxide  of  bismuth,  r^.j-Qg 

Certain  triatomic  bases  may  be  represented  as  monatomic, 
by  supposing  a  portion  of  the  oxygen  to  be  associated  with  the 
positive  radical ;  thus,  sesquioxide  of  uranium  U4O3  may  be 

represented  as  protoxide  of  uranyl,  tt^£a]  O;  and  teroxide  of 
antimony,  Sb203,  as  protoxide  of  antimony  1,  ci^riiO.     Non- 


*  The  radical  stibethyl  is  biatomic,  like  arsencthyl  (p.  527). 


ALCOHOLS.  531 

basic  bioxides,  or  peroxides,  may  be  represented  in  a  similar 
manner;  e.g.,  peroxide  of  hydrogen,  =      tt^"^' 

B,  AlcoJwls. — These  bodies,  all  of  which  belong  to  organic 
chemistry,  are  also  monatomic,  biatomic,  or  triatomic.  The 
primary  monatomic  alcohols,  or  alcohols  proper,  are  derived 
from  water  by  the  replacement  of  1  atom  of  hydrogen  by  a 
hydrocarbon  of  the  form  -G-nHan+i ;  -^011211-1 ;  or  ^0^20-7. 

a.  Alcohols  containing  radicals  of  the  form  ^nll2n+i« 
The  number  of  these  at  present  known  is  ten,  viz. : — 


Methylic  alcohol,  wood-spirit,  or^  __  .QH3  i^ 

hydrate  of  methyl  (protyl) .     .5         ^       ~      H     ■*     * 

Ethylic  alcohol,  spirit  of  wine,  oro      tt  £>   _   -^2^5  7  ^v 
hydrate  of  ethyl  (deutyl)     .     .5^2^^^   -      h     ^^• 

Propylic  alcohol,  or  hydrate  of^  _    QJJ  . 

trityl J^3^8^   -       H    ^^• 

Butylic    alcohol,    or  hydrate   ofi^^  ^^  -^4^9  m 
tetryl 5    ^    10  H    -^     * 

Amylic    alcohol,    or   hydrate    ofi      ^         =  ^-^n]Q. 
amyl(pentyl) 5    ^    12       -      H    ^     ' 

Caproic    alcohol,  or   hydrate   of^  ^^e^ulCL 

hexyl iH^H^  -      H   ^^• 

Caprylic  alcohol,  or  hydrate  of^^  _  "^sHni/:!. 

octyl .3^«^i«^   -       H    ^^• 

Cetylic    alcohol,   or    hydrate   of)  r\  ^^le^siln 

cetyl ^^16^34^-       H    ^^• 

Cerylic   alcohol,   or   hydrate   ofo^  ^  ^^-^zT^ssm 
ceryl 5    27    se  H  ^     ' 

Melissic  alcohol,  or  hydrate  ofi  n-^so^eilri 

meiissyl ^^30^^62^  -       H    ^^• 

The  first  of  these  liquids  is  found  among  the  products  of 
the  destructive  distillation  of  wood  ;  the  second,  third,  fourth, 
and  fifth,  are  formed  by  the  fermentation  of  saccharine  sub- 


532  WATER    TYPE. 

stances  ;  caprylic  alcohol  is  obtained  by  saponifying  castor-oil 
with  hydrate  of  potash  and  distilling  the  product  with  excess 
of  the  alkali  at  a  high  temperature  ;  cetylic  alcohol  is  obtained 
from  spermaceti ;  cerylic  alcohol  from  Chinese  wax,  and  me- 
lissic  alcohol  from  bees-wax. 

Compounds,  whose  formulae  differ  from  one  another  by 
n .  •GHg,  are  said  to  be  Jiomologous :  e.  g.,  the  alcohols,  the 
fatty  acids  (p.  538),  the  compound  ethers  (p.  545),  &;c. 

/3.  Alcohols  containing  radicals  of  the  form  CnHsn-i :  — 

jn  TT 

Acrylic  or  allylic  alcohol, -GgHgO  =     ^tt^]^'    This  is  the 

only  term  of  the  series  at  present  known. 

y.  Alcohols  containing  the  radicals,  OJi^n-i '  —  Of  this 
series,  there  are  two  isomeric  groups,  distinguished  by  their  be- 
haviour with  oxidising  agents,  the  bodies  of  the  one  group 
being  thereby  converted  into  aldehydes,  the  others  not.  To 
the  first  group  belong : —        . 


Benzoic  alcohol      .     .     -GyHg-Q     = 

^'g']©. 

Cuminic  alcohol     .     .     -GjoHi^Q  = 

^'°g>3]©. 

To  the  second : — 

Phenylic  alcohol,  car-^ 

bazotic  acid,  or  hy-     -QgHgO     = 
drate  of  phenyl  .     J 

^lf=}©. 

Cresylic  alcohol      .     .    -G^HgO     = 

^IjH']©. 

All  these  alcohols  contain  1  atom  of  hydrogen  replaceable  by 
a  metal ;  thus  :  common  alcohol,  treated  with  potassium,  gives 
off  one  sixth  of  its  hydrogen,  and  yields  ethylate  of  potassium, 

r\  TT 

\r  ^]  '^'    I*  is  not  found  possible  to  replace  another  atom  of 
hydrogen  in  a  similar  manner. 

Biatomic  Alcohols,  or  Glycols. — The  general  formula  of  these 

/"I    TT 

compounds  is     tt  ^"]^2-     Three  of  them  have  been  obtained. 


ALCOHOLS.  .    533 


viz.,  ethjlic  glycol,     |j  ^j  ^2^  propylic  glycol,    ^  ^]  O2; 

and  amylic  glycol,      tt  ^°]  Og.     The  2  at.  hydrogen  in  each 

of  these  formulae,  may  be  replaced  by  other  radicals  positive 
or  negative  ;  so  that  the  glycols  are  bibasic  and  biacid.  By 
mixing  iodide  of  ethylene,  ^2^4  •  -^ 2  ^'^^^  ^  atoms  of  acetate  of 
silver,  and  distilling  the  product,  a  distillate  of  acetate  of  gly- 
col is  obtained,  while  iodide  of  silver  remains  behind  :  — 

e.HJ,  +  2gg^  =  2  Agl  +  (^^2^5^ 

Acetate  of  silver.  Acetate  of  glycol. 

and  acetate  of  glycol  distilled  with  hydrate  of  potash  yields 
glycol  and  acetate  of  potash  : —  ^ 

The  propylic  and  amylic  glycols  are  obtained  in  a  similar 
manner  with  bromide  of  propylene  and  bromide  of  amylene. 

Tr {atomic  Alcohols,  or  Glycerines, — The  general  formula  of 

P    TT 

these  compounds  is  "tt^"~M'^3'  'The  three  atoms  of  hy- 
drogen which  they  contain  may  be  wholly  or  partly  replaced 
by  radicals  positive  or  negative.  One  term  of  the  series  has 
been   long    known,   viz.  :    ordinary   glycerine,  ■QgHgOg    = 

jT^   TT 

V]  O3.     The    neutral  fats,  olein,  stearin,  palmitin,  &c., 

consist  of  glycerin,  in  which  the  3  atoms  of  free  hydrogen 
are  replaced  by  acid  radicals;    eg.,  stearin,  G^-j^hqQ-q  = 

jQ    TT 

/£2  TT   A\  ]  ^3-    A  great  number  of  similar  compounds  have 

been  formed  artificially  by  heating  glycerine  with  acids. 
Conversely,  when  neutral  fats,  stearin  for  example,  are  heated 

VOL.  II.  P  P 


534  WATER  TYPE. 

with  hydrate  of  potash,  or  other  metallic  oxides,  the  acid  radical 
passes  to  the  metal,  forming  a  salt,  and  glycerine  is  formed,  e.g., 

(e?sb%)3^^3+  3  (go) =3  f .  A.O)o3+  ^^Is  ja. 

This  is  the  process  of  saponification.  Glycerine  may  also  be 
formed  synthetically,  viz.  by  heating  the  terbromide  of  allyl, 
^^gHgBrg  with  acetate  of  silver.  Teracetate  of  glycerine  (tri- 
acetin)  is  thus  formed ;  and  this,  when  heated  with  hydrate 
of  baryta,  yields  glycerine.  The  other  glycerines  have  not 
yet  been  obtained  in  the  free  state ;  but  the  acetate  of  ethyl- 

d  XT 

glycerine,  /ri  TT  o^  ^  ^s'  '^^  obtained  at  the  same  time  as  gly- 
col,  by  the  action  of  iodide  of  ethylene  on  acetate  of  silver. 

The  secondary  alcoJiols,  or  Ethers,  bear  the  same  relation  to 
the  primary  alcohols  that  anhydrous  metallic  oxides  bear  to 

Q   XT 

the  hydrates;  e.^.,  amy  lie  alcohol,     ^tt^^J-Q-;  amylic  ether, 

Q  H    ^ 

^5"  11 

There  are  likewise  ethers  containing  two  different  radicals ; 

e,  g.,  methyl-amylic  ether,  ^  tt^  ]0.    Ethers  may  be  formed 

■^5^^  11 

by  the  action  of  the  iodides  of  methyl,  ethyl,  &c.,  on  alcohols 
in  which  1  atom  of  hydrogen  is  replaced  by  potassium ;  thus, 
common  alcohol  treated  with  potassium  gives  off  hydrogen, 
and  yields  CgHgKO;  and  this  compound  treated  with  iodide 
of  amyl,  yields  ethyl-amylic  ether : — 

^»K=]a  +  G,H„I  =  KI  +  §H°  ^^- 

The  same  potassium-alcohol  treated  with  iodide  of  ethyl, 
yields  common  ether  :  — 

^2H5p  +  ^^H,.  I  =  KI  +  §{5;}0. 


ACIDS.  535 

Ethers  are  also  formed  by  the  action  of  strong  sulphuric  acid 
on  the  alcohols,  as  will  be  more  fully  explained  hereafter. 

C. — Aldehydes.  —  These  compounds  differ  from  the  alcohols, 
in  containing  2  atoms  of  hydrogen  less.     Thus,  to  an  alcohol, 

^nH2n+ij^^   there   corresponds    an    aldehyde,    ^"^^^-^lO. 

They  are  obtained  by  the  action  of  oxidising  agents  on  the 
alcohols.  Thus,  common  alcohol  treated  with  bichromate  of 
potash  and  sulphuric  acid,  yields  ethylic  or  acetic  aldehyde, 

H  ^^• 

There  are  likewise  aldehydes  corresponding  to  the  other 

series  of  alcohols.  Thus,  to  the  alcohols  containing  the  radicals, 

^J^2vi-v  there  correspond  aldehydes  containing  radicals  of 

rj,  XT 
the  form  ^nH2n_9.    Oil  of  bitter  almonds,  •G7HgO=    ^tt^]0, 

belongs  to  the  series. 

The  aldehydes  are  especially  distinguished  by  forming  crys- 
talline compounds  with  the  alkaline  bisulphites ;  6.  g.,  sulphite 

of  acetosyl  and  sodium,  Cg^sNaO, -802= £^  TT    -vr  \^2' 

One  atom  of  hydrogen  in  the  radical  of  an  aldehyde  may 
be  replaced  by  an  alcohol-radical ;  the  compounds  thus  pro- 
duced are  called  ketones.     Thus,  acetone,  GgHgO,  the  ketone 

of  the  acetic  series,  is     ^    ^^    tt^  ]^» 

Acids,  or  Negative  Oxides. — These,  like  the  positive 
oxides,  are  divided  into  primary  or  hydrated,  and  secondary 

or  anhydrous.   Thus,  hydrated  nitric  acid,    -rj  ^  JO ;  anhydrous 

nitric  acid,  -vtm^]^- 

Acids  are  also  monatomic,  like  nitric  acid  just  noticed,  and 
acetic  acid,    ^    a    j^.  biatomic,  like  sulphuric  acid,  tt  ^l-O-g; 

p  p  2 


536  WATER   TYPE. 

or    triatomic,    as    phosphoric    acid,    tt   1  -Og ;     citric    acid, 

A  monatomic  hydrated  acid,  having  only  one  atom  of  re- 
placeable hydrogen,  is  necessarily  monobasic ;  a  biatomic 
acid,  having  two  atoms  of  replaceable  hydrogen,  is  generally 
(but  not  necessarily)  bibasic ;  a  triatomic  acid,  generally  tri- 
basic.  The  determination  of  the  basicity  of  an  acid  is  a 
matter  of  some  difficulty.  In  many  cases,  the  formation  or  non- 
formation  of  acid  and  double  salts  may  serve  as  a  distinction. 

Thus,   tartaric   acid,  which  is  a  bibasic   acid,      ^tt"^    '^]^2'> 

iCj  H"  O. 

forms  a  neutral  tartrate  of  potash,     '^j^'*    '*]'^2>  ^"^  ^"  ^^'^^ 

tartrate,       4^tt  ''j-^2  5    ^^f   likewise,   sulphuric    acid   forms 

'S'K204,  and  •S-KH04 ;  whereas  nitric  acid,  having  but  one  atom 
of  hydrogen,  forms  but  one  potash-salt,  viz.  NKO3.  But  acetic 

acid,  generally  regarded  as  monobasic,  Q^llJ^^^    ^    3    JQ^ 

also  forms,  not  only  a  neutral  potash-salt,  Q^H^KQ^^^  but  like- 
wise, an  acid  potash-salt,  usually  represented  by  the  formula 
^gHgKOg .  'G2H4O2 ;  but  if  the  formula  of  acetic  acid  be 
doubled,  making  it  C^HgO^,  the  neutral  potash-salt  will  be 
•G^HgKgO^,  and  the  acid  salt,  QJiQ(K}l)Q-^.  Acetic  acid  will 
thus  be  represented  as  a  bibasic  acid;  and  in  fact,  this  quantity, 
e^HgO^  (=  120),  is  the  equivalent  of  ^SHgO^  (  =  98),  that  is  to 
say,  it  saturates  the  same  quantity  of  potash.  Why,  then,  is 
acetic  acid  universally  regarded  as  monobasic  ?  On  this  point, 
we  shall  quote  the  observations  ofGerhardt:  — 

"  The  basicity  of  acids  is  a  question,  not  of  equivalents,  but 
of  molecules. .  .  .  If  we  examine,  under  the  same  volume,  the 
composition  of  the  vapour  of  certain  volatile  bodies,  correspond- 
ing to  the  acids,  and  compare  together  the  similar  terms,  such 
as  the  chlorides  of  the  acid  radicals,  or  the  neutral  compound 
ethers,  we  observe  perfectly  regular  differences,  which  are 


ACIDS.  537 

always  related  to  the  chemical  properties  of  the  corresponding 
bodies:  thus, — 

,     „  f  Chloride  of  acetyl      .  contain  CI .  -GgHgO. 
1  Chloride  of  sulphuryl       „        Clg . -SOg. 


2  vol.  of, 


Acetate  of  methyl     .  contain     j^A    JO, 


3 


Sulphate  of  methyl    .      „        mH^  ^^2* 


In  the  same  volume^  therefore,  chloride  of  acetyl  contains  the 
radical  chlorine  once,  while  chloride  of  sulphuryl  contains  it 
twice :  In  the  same  volume,  again,  sulphate  of  methyl  contains 
twice  the  quantity  of  methyl  that  is  contained  in  the  acetate. 
With  these  differences  of  composition  of  the  chlorides  and 
neutral  ethers,  are  connected  other  properties,  such  as  the  fol- 
lowing:—  Acetic  acid  forms  but  one  compound  ether  (p.  545), 
whereas  sulphuric  acid  forms  two,  a  neutral. and  an  acid  ether; 
acetic  acid  forms  but  one  amide  (p.  557) ;  sulphuric  acid  forms 
several,  &c.  In  short,  on  inquiring  what  are  the  smallest  quan- 
tities of  the  radicals,  acetyl  and  sulphuryl,  that  are  concerned 
in  chemical  metamorphoses,  we  find  that  they  are  QJIJ^, 
equivalent  to  H^  and  -SOg  equivalent  to  Hg ;  hence,  we  are 
led  to  represent  the  molecule  of  acetic  acid  as  monatomic,  and 
that  of  sulphuric  acid  as  biatomic." 

The  principal  monobasic  inorganic  acids  are  nitric,    -rj  ^JO, 

hypochlorous,  ttI-O-,    chloric,    tt  ^]0,  and  metaphosphoric. 

Of  monobasic  organic  acids,  the  most  important  are  the 
so-called  fatty  acids,  whose  general  formula  is  — 


c„H,„a,  =  '^»H|"-'^ia 


They  correspond  to  the  alcohols  -G-nHsn+iO,  and  those  which 
contain  the  same  number  of  carbon  atoms  as  the  known 
alcohols  may  be  obtained  from  the  latter  by  the  action  of 

p  p  3 


Formic    acid 

-GH^e^ 

CEnanthylic  acid  €7  Hi^Og 

Palmitic 

Acetic         „ 

e,H,  o. 

Caprylic             „  €-,  H.^-^^ 

Stearic 

Propionic    „ 

•03H,0, 

Pelargonic         „  O9  HjgOj 

Cerotic 

Butyric       „ 

^4Hs^, 

Rutic  or  capric  „   OjoHjoOa 

Melissic 

Valerianic  „ 

"^5Hio"^2 

Laurie                „  OijHj^Os 

Caproic       „ 

^eH.A 

Myristic             „  G^^Hag-Ga 

538  WATER   TYPE. 

oxidising  agents,  such  as  chromic  acid.    The  number  of  these 
acids  at  present  known  to  exist  is  sixteen,  viz. :  — 


These  acids  occur  in  the  vegetable  and  animal  organism ; 
they  are  formed  by  the  saponification  of  fats,  and  by  the  action 
of  oxidising  agents  on  fatty  and  waxy  matters,  and  on  albumin, 
fibrin,  casein,  &c.  The  first  ten  acids  of  the  series  are  liquid 
at  ordinary  temperatures;  the  next  four  are  solid  fats;  the 
last  two  are  waxy.  Cerotic  acid  is  obtained  from  Chinese 
wax ;  melissic  acid  from  bees-wax. 

A  second  series  of  monobasic  organic  acids  consists  of  acids 
whose  radical  is  of  the  form  QJlzn-zO-;    e.g.,  oleic  acid, 

■GigHg^Og  =     ^^Ti^^]0'j    obtained    by   the    saponification    of 

various  fixed  oils.  A  third  series  consists  of  acids  whose  radical 
has  the  form  -G-nHau.g-Q.     These  are  called  the  aromatic  acids  ; 

p  TT  r\ 

only  three  of  them  are  known,  viz.  benzoic  acid,     ^tt^    JO; 

toluicacid,     ^tt^    jO,  and  cuminic  acid,     ^^xj^^     ]0. 

There  are  a  few  monatomic  organic  acids  not  included  in 
either  of  these  groups,  among  which,  must  be  particularly  men- 

tioned  cyanic  acid,    tt  ]  '^'      The  cyanates  are  formed  from 

the  cyanides  by  oxidation ;  thus,  cyanide  of  potassium  fused 
with  oxide  of  lead,  or  bioxide  of  manganese,  yields  cyanate  of 
potash,  ^NKO. 

Bibasic  acids. — These  acids,  as  already  observed,  generally 
form  two  salts,  a  neutral  and  an  acid  salt,  and  are  peculiarly 
inclined  to  form  double  salts ;  e.  g.  potassio-cupric  sulphate, 

ifa'^^^;  tartrate  of  potash  and  soda,  ^i^^^i'^2- 


ACIDS.  539 

With  the  alcohols  they  form  two  compound  ethers,  a  neutral 
and  an  acid  ether  ;  e.  g.,  neutral  oxalate  of  ethyl,  fjrh\  i^2» 

acid   oxalate   of    ethyl,  or  oxalovinic  acid,    tt  fjr^TJ^\  S  ^2* 

Within  the  same  vapour  volume,  the  neutral  ethers  of  the  hihasic 
acids  contain  twice  as  much  of  the  alcohol-radical  as  the  neutral 
ethers  of  the  monobasic  acids  (p.  545).     Thus,  2  vols,  oxalate  of 

ethyl  =  .So  \  ]0;  2  vols,  benzoate  of  ethyl  =  ^^^JO. 

(,■^2  "^5/2  ^2"^5 

The  chlorides  of  hihasic  acids  (obtained  by  the  action  of 
pentachloride  of  phosphorus  on  the  acids)  contain,  within  a 
given  vapour  volume,  twice  as  much  chlorine  as  the  chlorides  of 
the  monobasic  acids  (p.  549). 

The  principal  bibasic  inorganic  acids  are  carbonic,  tt  j  -^2  > 

sulphurous,  TT  ]'02  5    sulphuric,     Tr^jOg;  and  chromic  acid, 

A  ^jOg.  Pyro-phosphoric  acid,  PgH^O^,  may  be  regarded  as 

p   TT  jQ 

bibasic  acid,  containing  the  radical  PgHgQ^;  viz.,     ^tt^    ^  j  q.^  . 

or  as  a  compound  of  metaphosphoric  and  ordinary  phosphoric 
acid. 

The  greater  number  of  the  bibasic  organic  acids  may  be 
arranged  in  three  groups,  viz. :  — 

a.— Acids  whose  general  formula  is      "    g""*    ^l^a*    Eight 

of  these  are  known,  viz.: — Oxalic  acid,     |t  ^]  Og;  succinic 

acid  (^4);  pyro-tartaric  (-G-g);  adipic  (^g);  pimelic  (-G;) ; 
suberic  (-Gg) ;  anchoic  (>Gg) ;  and  sebacic  acid  (-Gjq).  They 
are  formed  by  the  action  of  oxidising  agents  on  fatty  matters, 
and  are  related  to  the  monobasic  fatty  acids  GJl^vf^i  ^7  the 
relation  — - 

'^nH2n^2^4    =    ^^^2    +    ^n-lH2n^2^2 

e.g.,  fiHA.   =  €0,  +      G^,^ 

Succinic  acid.  Propionic  acid, 

p  p  4 


540  WATER   TYPE. 

^.-General    formula:   (^"^fn- A)2j  ^^^     For  example, 

■"2 

lactic  acid  =  Qq^i^^q  =  ^^^^^^^Q^. 

y.— General  formula:  ^"^ff  ^^^^j^^.    Two  acids  of  this 

group  are  known,  viz.,  phthalic  acid,  ^gHg04,  obtained  by 
the  action  of  nitric  acid  on  bichloride  of  naphthalin,  and 
insolinic  acid,  •Q9H8O4,  bj  the  action  of  chromic  acid  on 
cuminic  acid.  They  are  related  to  the  aromatic  acids  in  the 
same  manner  as  the  acids  a  to  the  fatty  acids.     Thus  :  — 


e^HgO^    =  QQ,    -f    ^sHgO^ 


Insolinic  acid.  Toluic  acid. 

Of  bibasic  acids  not  included  in  the  preceding  groups,  the 

jQ  XT    Q 

most  important  are  malic  acid,  •G^HgOg   =      ^tt''    ^]^2'  ^'"^^ 
tartaric  acid,  ^411606  =  ^^S^'^^jOg. 

Trihasic  acids. — These  acids,  containing  three  atoms  of  re- 
placeable hydrogen,  form  three  kinds  of  salts,  viz.,  one 
neutral,  and  two  acid  salts.     Thus,  from  tribasic  phosphoric 

acid,  PH3O4   =  -^jOg  are  formed  PH2Ka4,  PHK2a4,  and 

PK3©,. 

With  alcohols  they  form  three  compound  ethers.  Phos- 
phoric acid  and  common  alcohol  yield  ethylophosphoric  acid, 
VUJ^Qfi,)(^,',  bi-ethylophosphoric  acid,  VI{{Q^YL,\Q>^i 
phosphoric  ether,  P(.G2H5)304. 

The  neutral  ethers  of  trihasic  acids  contain^  within  a  given 
vapour  volume,  three  times  as  much  of  the  alcohol  radical  as  the 
ethers  of  the  monobasic  acids.  Thus,  2  vols,  citric  ether  contain 

^^^^ja,;  and  2  vols,  acetic  ether  contain  *S,^^^0. 

(^2^5)3'        '  -^2^5     ^ 

The  chlorides  of  the  tribasic  acid  radicals  contain ,  within  a 
given  volume,  three  times  as  much  chlorine  as  the  chlorides  of  the 
monobasic  acid  radicals.     Thus,  2  vols,  chloride  of  phosphoryl 


ACIDS.  541 

(oxychloride  of  phosphorus)  contain  PO .  CI3 ;  and  2  vols, 
chloride  of  benzoyl  contain  Q^llfi-  .01. 

The  tribasic  mineral  acids  are, — boracic  acid,  BH3O3; 
phosphorous  acid,  PH3O3;  phosphoric  acid,  PH3O4;  and 
arsenic  acid,  AsHgOg. 

Five  tribasic  organic  acids  are  known,  viz. :  — 

Cyanuric  acid  e6H3N303  =  ^I^]^y 
Citric  acid  .  CfiHgO^  =  ^^^'^^jOa. 
Aconitic  acid.  GtqH^Q-q  =  "^Su^^'lOg. 
Meconic  acid  .  Q^ll^Q^  =  ^^u^^jOg. 
Chelidonic  acid   Q^U.O,  =  ^^^^'}Q^. 

Cyanuric  acid  may  be  regarded  as  a  triple  molecule  of 
cyanic  acid.  It  is  formed  by  the  destructive  distillation  of 
uric  acid,  by  the  action  of  chlorine  gas  on  urea,  and  by  the 
action  of  water  on  fixed  chloride  of  cyanogen,  CygClg.  Aconitic 
acid  is  obtained  by  the  destructive  distillation  of  citric  acid. 
Meconic  acid  is  contained  in  opium,  and  chelidonic  acid  in 
the  chelidonmm  majus. 

Conjugated  acids, — This  name  is  given  to  acids  contain- 
ing a  conjugated  radical.  Thus,  there  are  chloro-,  hromo-, 
and  iodo-conjugated  acids,  containing  chlorine,  bromine,  or 
iodine  in  place  of  hydrogen  in  the  radical  ;  e,  g.,  chloracetic 
acid,'^2(Cl2H)Oj^.  terchloracetic  acid,  ^^^^^j  O ;  mtro- 
conjugated  acids,  containing  NOg;    e.g.,  nitro-benzoic  acid, 

7    4V       2/^j  Q  .    sulpho-conjugated  acids,  containing  SQ^  ; 

e  ^.,  sulpho-benzoic  acid,     ^    '^Vr    ^^    iQ^,  8ic, 


542  WATER   TYPE. 

These  acids  are  formed  by  the  action  of  sulphuric  acid, 
nitric  acid,  chlorine,  &c.,  on  the  primitive  acids : — 

a. — Jmidogen  acids. — These  are  derived  from  hydrate  of 

NIT 

ammonium,    ^  '' jO,  by  the  substitution  of  an  acid  radical  for 

two  or  more  atoms  of  the  hydrogen  in  ammonium.    Thus : — 
Sulphamic  acid  .     .     SHgNOa     =  "^^l^^  ^O. 

Phosphamic  acid     .     PH^NO^     =   ^^^^)  jO. 

Osmiamicacid   .     .     Os^HNOg    =  ^(^2^2) jq. 

Oxamicacid      .     .     e^HgNOg    =  ^^2(^2^2)  jq. 

These  acids  are  formed  by  the  action  of  ammonia  on 
the  anhydrides,  or  by  the  action  of  heat  on  the  acid  am- 
monia-salts of  bibasic  acids,  an  atom  of  water  being  thus 
eliminated :  — 

•^2^2    la   _«  TT  £1  —  ^"^2(^2^2)^1:1 

"  ~r ~- — '  *~~~" Y 

Acid  oxalate  of  Oxamic  acid, 

ammonia. 

Anhydrous  Acids,  or  Anhydrides. — These  com- 
pounds are  formed  by  the  substitution  of  an  acid  radical 
for   the   whole  of  the  hydrogen   in  one  or   two  molecules 

of  water,  thus: — citric  anhydride  NgOg^  vro^}^;  sulphuric 

anhydride  •^Q3  =  SQ2.0;    phosphoric   anhydride   PgO^  = 


ANHYDRIDES.  543 

Anhydrous  nitric  acid  is  obtained  by  the  action  of  chlorine 
on  dry  nitrate  of  silver.  The  anhydrides  of  bibasic  acids 
may  be  formed  by  the  abstraction  of  water  from  the  hydrated 
acids,  either  by  heat  or  by  the  action  of  anhydrous  phosphoric 
acid  ;  e.  g, :  — 

^2  ^^ r ' 

^-^-i— X.— i*^--'  Succinic 

Succinic  acid.  anhydride. 

The  bibasic  acids  may,  indeed,  be  supposed  to  contain  water. 
Thus,  succinic  acid  =  -Q^H^Og .  O  +  HgO.  But  the  anhy- 
drides of  the  monobasic  acids  cannot  be  obtained  in  this  way ; 
in  fact,  according  to  the  formulae  of  the  unitary  system,  they 
do  not  contain  water,  and  even  supposing  HgO  to  be  abstracted 
from  them,  the    remainder  will  not  be  the  formula  of  the 

anhydrides :  thus,  the  formula  of  acetic  acid  being     ^    a    \  Q,^ 

the  abstraction  of  HgO  would  leave  ^2^2^  J  whereas,  the 

p  TT  r\ 

formula  of  anhydrous  acetic  acid  is  riTx^r\\  0=2  x  Q^fi^, 

This  is  a  fact  which  the  ordinary  formulae  do  not  explain.  If 
the  formula  of  hydrated  acetic  acid  be  C4H4O4  =  C4H3O3.  HO, 
it  is  by  no  means  evident  why  the  HO  should  not  be  separated 
from  it,  and  leave  the  anhydrous  acid. 

The  anhydrides  of  organic  monobasic  acids  are  obtained  by 
the  action  of  the  chlorides  of  their  radicals  on  the  alkaline 
salts  of  the  acids  ;  thus : — 

^A^ja  +  e^HgO.ci  =  KCi  +  ^^H^^Jo. 

^~-- Y -^  Chloride  of  ."- — ; — ^^ ^ 

Acetate  of  acetyl.  Acetic  anhydride, 

potash. 

There  are  some  organic  anhydrides  containing  two  different 
radicals ;  thus,  by  the  action  of  chloride  of  benzoyl  on  acetate 
of  potash,  aceto*benzoic  anhydride  is  formed  : — 

^^^a^jo  +  a^Hsa.ci  =  KOI  +  ^^Ho^^- 


544  WATER   TYPE. 

These  compounds   are  resolved  by  heat  into  the   simple 
anhydrides,  thus : — 


Oxygen-salts,  or  Intermediate  Oxides.  —  Salts 
are  formed  by  the  substitution  of  a  metal  or  other  positive 
radical  for  the  basic  hydrogen  of  an  acid,  and  may  there- 
fore be  regarded  as  water,  the  hydrogen  of  which  is  re- 
placed partly  by  a  basic,  partly  by  an  acid  radical.  If  all 
the  basic  hydrogen  of  the  acid  is  thus  replaced,  the  salt  is 
neutral  or  normal;  if  only  part  of  the  hydrogen  is  thus  re- 
placed, the  salt  is  acid ;  and  such  salts  may  be  regarded  as 
compounds  of  neutral  salts  with  the  free  acid,  thus : — 

/  gp  ,       N  so  ■>  so 


]o,)  =  ^^]o,  +  ^;]o, 


Bisulphate  of       Sulphuric  acid.       Neutral  sulphate 
soda.  of  soda. 

(^2"^3^)2]ri     —   ■^2"^3^  ?  o     I     ■^2^3'^  ^n. 
KH     i^2    -        H      i^    +         K     ^^' 

Biacetate  of  potash.  Acetic  acid.  Neutral  acetate 

of  potash. 

Basic  salts  may  be  regarded  as  compounds  of  a  neutral 
salt  and  an  oxide,  or  as  double  or  triple  molecules  of  water, 
in  which  the  hydrogen  is  replaced  by  a  positive  radical  in  a 
larger  proportion  than  is  required  to  form  a  neutral  salt; 
thus : — 

Pbg  3  ^2  -   pbi  ^   +       Pb    J  ^• 

Subacetate  of       Oxide  of  lead.       Neutral  acetate 
lead.  of  lead. 


Subsulphate  Oxide  of        Neutral  sulphate 

of  copper.  copper.  of  copper. 


COMPOUND   ETHERS.  545 

In  the  neutral  salts  of  sesquioxides,  as  in  the  oxides  them- 
selves, 3  at.  hydrogen  of  the  type  water  are  replaced  by  2  at. 
of  the  metal ;  thus  — 

(-^^2/3 1  o.  .  (^^2)3 1  o. 

Fe^   -J^a'  Fe^  ^  ^«* 

Ferric  nitrate.  Ferric  sulphate. 

Compound  ethers.  When  the  basic  hydrogen  of  an  acid  is 
replaced  by  an  alcohol-radical,  the  product  is  a  compound 
ether ;  these  compounds  may  also  be  regarded  as  alcohols  in 
which  one  atom  of  hydrogen  is  replaced  by  an  acid  radical. 
As  already  observed,  monobasic  acids  form  but  one  compound 
ether ;  bibasic  acids  form  two,  a  neutral  and  an  acid  ether ; 
and  tribasic  acids,  one  neutral  and  two  acid  ethers.  The  acid 
ethers  are  true  acids,  and  form  salts.  Thus,  from  sulphuric 
acid  are  formed  — 

Neutral  sulphate  of  ethyl   =  //-.  tt^n  ]  Oo,  and 

SO 
Acid  sulphate  of  ethyl,  or    __       tt^  (  jQ 

sulphovinic  acid  ""    £1  TT  ^      ^' 

The  remaining  atom  of  hydrogen  in  the  latter  may  be  re- 
placed by  K,  Na,  &c. 

From  citric  acid  are  formed  — 

Neutral  citrate  of  methyl      .     .     .    /^'u'P'J  ^3 

Citrobimethylic  acid  (monobasic)     .    (-^113)2  >  O3 

H        ^ 

Citromonomethylic  acid  (bibasic)    .     -GHg     /  O3 

The  glycerides  or  neutral  fats  (p.  533)  also  belong  to  the 

compound  ethers,  being  derived  from  a  triatomic  alcohol  or 

glycerine  by  the  substitution  of  an  acid  radical  for  the  replace- 

r\  XT 
able  hydrogen ;  e,g.y  triacetin  =  ,^  A  An  jOg. 

V'^2"3^>'3 


546  WATER   TYPE. 

SULPHIDES,   SELENIDES,    TELLURIDES. 

The  formulae  of  these  bodies  are  precisely  similar  to  those  of 
the  oxides,  being  derived  from  hydrosulphuric  acid,    Tr]^t 

&c.  just  as  the  oxides  are  derived  from  w^ater.  These  series, 
however,  especially  the  selenides  and  tellurides,  are  much 
less  complete  than  that  of  the  oxides. 

The  analogy  between  the  metallic  sulphides  and  oxides  has 
been  sufficiently  pointed  out  in  the  preceding  part  of  this  work. 
The  alkali-metals,  potassium,  sodium,  &c.,  form  hydrated  sul- 
phides,  or   hydro-sulphates,   such  as  tt]^^  ttJ'^^&c.;  and 

K 

anhydrous  sulphides,  tA  ^9  &c.     Most  of  the  other  metals 

form  only  anhydrous  sulphides. 

The  alcoJiolic  sulphides,  primary  and  secondary,  bear  the 
same  relation  to  hydrosulphuric  acid  that  the  alcohols  and 
ethers   bear   to    water.      The   primary   alcoholic   sulphides, 

jQ   TT 

°TT^°'*'^}  "S,  generally  called  mercaptans,  are  fetid  oils,  or  crys- 
talline solids,  which  are  obtained  by  the  action  of  the  alkaline 
hydrosulphates  on  the  chlorides  of  the  alcohol  radicals ;  — 

C,H,C1  +  ^]»  =  KCl   +  ^^2^}S; 

Chloride  of  Ethylic  mer- 

ethyl.  captan. 

or  by  tlie  action  of  the  same  alkaline  hydrosulphates  on  the 
sulphovinates  or  homologous  salts :  — 

The  basic  hydrogen  in  the  mercaptans  may  be  replaced  by 
metals,  forming  compounds  called  mercaptides;  e.  g.,    A  ^]  ^. 


SULPHUR-ACIDS.  547 

The  secondary  alcoholic  sulphides  or  hydrosulphuric  ethers 
are  obtained  by  the  action  of  the  anhydrous  alkaline  sulphides  ' 
on  the  chlorides  of  the  alcohol-radicals :  — 

2€2H,C1  4-  |]^  =  2KC1  +  q'^']^' 

Sulphur-acids.  —  The  mineral  sulphur-acids  are  but  little 
known  in  the  hydrated  state.  The  anhydrous  sulphur-acids 
are  analogous  to  the  oxygen-acids.    Thus,  sulpharsenious  acid, 

A  ]  ^3,  sulpharsenic  acid,   *    J'S-g,  the  arsenic  being  triatomic  ^ 

in  the  former,  and  pentatomic  in  the  latter. 

But  few  organic  sulphur-acids  have  been  obtained.   Hydro- 

sulphocyanic  acid,  -GNH^  =  tt  }  S'j  is  analogous  to  cyanic 
acid,  Tj  ]0.  Its  potassium-salt  is  obtained  by  heating  sul- 
phur with  ferrocyanide  of  potassium  (I.  532). 

Thiacetic  acid  ^  3  j^^  jg  obtained  by  the  action  of 
pentasulphide  of  phosphorus  on  acetic  acid :  — 

This  reaction  is  instructive  when  viewed  in  relation  to  that  of 

pentachloride  of  phosphorus  on  acetic  acid ;  the  latter  giving 

rise  to  two  chlorides,  Q^Yi^Q^ .  CI,  and  HCl,  whereas  the  action 

of  the  sulphide  of  phosphorus  yields  not  two,  but  one  sulphur 

•d  TT  O 
compound,     ^    s    |  §^     ^  similar  difference  is  observed  in 

the  action  of  the  sulphide  and  chloride  of  phosphorus  on  al- 
cohol, the  former  producing  a  single  compound,  viz.  mercap- 

tan,  the  sulphide  of  ethyl  and  hydrogen,     ^tt^]^»   the    latter 

producing  two  separate  compounds,  viz.  Q.fi^CX,  and  HCl. 
This  difference  of  action  shows  in  a  striking  manner  the  pro- 


548  HYDROCHLORIC   ACID   TYPE. 

priety  of  representing  the  oxides   and  sulphides  by  a  type 
containing  two  atoms  of  hydrogen,  and  the  chlorides,  bro- 
mides, &c.,  by  a  type  containing  only  one  atom  of  hydrogen. 
Sulphur-salts.  —  These  compounds  are  formed  from  the  type 

TT 

tt}S,  by  the  substitution  of  a  positive  and  a  negative  radical 
for  the  tvv'o  atoms  of  hydrogen ;    Thus,   monobasic  sulph- 

arseniate   of  potassium,    -it-  j-Sj ;    tribasic    sulpharseniate    of 

AsS 
potassium,    ^    jSg;  these  formulas  are  evidently  analogous 

to  those  of  the  monobasic  and  tribasic  phosphates. 

The  compound  sulphur-ethers  are  sulphur-salts,  in  which  the 
positive  element  is  an  alcohol  radical:— For  example,  sulpho- 

cyanide  of  ethyl,  ^-L  ]S;  sulphocyanide  of  allyl,  or  oil  of 

mustard,  =  p,  X  }  S. 

Sulphide  of  acetyl  and  ethyl,  or  thiacetic  ether,  is  obtained 
by  the  action  of  persulphide  of  phosphorus  on  acetic  acid:  — 


HYDROCHLORIC   ACID   TYPE. 

Chlorides.  —  The  basic  metallic   chlorides  are,  like  the 
oxides,  either  monatomic  or  polyatomic ;  e.  g.  — 

KCl  PtClg  Fe^Clg.AuClg. 


monatomic.  biatomic,  triatomic. 

The  biatomic  and  triatomic  chlorides  unite  with  the  mon- 
atomic chlorides,  forming  crystalline  compounds,  whose  com- 
position may  be  illustrated  by  the  formulae  of — 

Chloro-aurate  of  sodium   .     .   NaCl.AuCl3=    Au^^^*' 


CHLORIDES.  549f 

■M"TT 

Chloroplatinate  of  ammonium,  NH^Cl .  PtClg  =  pf  '^  1  ^h' 

The  chlorides  of  gold  and  platinum  form  similar  compounds 
■with  the  hydrochlorates  of  the  organic  bases,  which  may  be 
represented  by  analogous  formulae.     Thus,  chloroplatinate  of 

ethylamine,  ^^Ha  NH  rC  H  ^. 

H    [N.HCI  +  PtCl^  =  ^^^3^^2^^^]Cl3. 

The  hydrochlorate  of  any  organic  alkali  may  be  represented 
as  the  chloride  of  a  basic  radical  containing  an  additional  atom 
of  hydrogen,  just  as  sal-ammoniac  may  be  represented  either 
as  NH3 .  HCl,  or  as  NH^Cl.  Thus,  hydrochlorate  of  ethyla- 
mine, NH^Ce^Hs).  HCl  =  NH3(€2H5) .  CI. 

The  chlorides  of  the  alcohol-radicals,  or  hydrochloric  ethers, 
are  obtained  either  by  the  action  of  hydrochloric  acid,  or  one 
of  the  chlorides  of  phosphorus,  on  the  alcohols:  — 

^Ajo  +  HCl  =  ^]Q  +  G,U,.Cl. 


(C.H.to) 


PCI3  =  l]0,  +  3  (^H^). 

'  Chloride  of 

Alcohol.  Phosphorous  ethyl. 

acid. 

These  chlorides  are  more  volatile  than  the  corresponding 
alcohols. 

The  acid,  or  negative  chlorides,  are  also  monatomic,  biatomic, 
or  triatomic,  according  to  the  acids  from  which  they  are 
derived. 

The  monatomic  chlorides,  derived  from  one  atom  of  hydro- 
chloric  acid,  contain,  in  two  vapour-volumes,  one  atom  of  chlorine, 
capable  of  forming  a  metallic  chloride  with  mineral  alkalies ;  e.g., 
chloride  of  cyanogen,  .GNCl  =  Cy .  CI ;  chloride  of  acetyl,  = 
■G2H3O.CI.  They  are  obtained  by  the  action  of  one  of  the 
chlorides  of  phosphorus  on  the  acids,  thus  :  — 

VOL.  IL  .  Q  Q 


550  HYDROCHLORIC   ACID   TYPE. 

Perchloride  of  *" 1 ^         Oxychloride 

phosphorus.        Chloride  of  acetyl     of  phosphorus. 
+  hydrochloric  acid. 

3(^A©]o)    +  PCI3  =  |j©3  +  3(C,H30.C1). 

Or,  by  the  action  of  oxychloride  of  phosphorus  on  an  alkaline 
salt  of  the  same  acid: — 

(^A^ja)  +  PO.  CI3  =  ^^}03  +  3  (G,H30.C1), 

The  biatomic  diloridesj  derived  from  two  molecules  of  hydro- 
chloric acid,  contain,  within  two  vapour-volumes,  two  atoms  of 
chlorine,  capable  of  forming  a  metallic  chloride  with  alkalies :  — 

Chloride  of  carbonyl,  oxychloride  of 
carbon,  or  phosgene =  ^O  .  Clj 

Chloride  of  sulphuryl =  ^Og .  Clg 

Chloride  of  succinyl =  -Q^H^O^ .  Clg 

Chloride   of    chromyl,    or    chloro- 

chromic  acid  .......  =  CrgOg .  Clg 

These  chlorides  may  be  obtained  by  the  action  of  penta- 
chloride  of  phosphorus  upon  the  corresponding  anhydrous 
acids. 

The  action  of  pentachloride  of  phosphorus  on  a  bibasic  acid 
is  supposed  by  Gerhardt  to  consist  of  two  stages, — the  first 
being  the  formation  of  an  anhydrous  acid,  the  second  the  con- 
version of  that  compound  into  a  chloride.     For  example  :  — 

^'^'h'  ; O  ^  +  ^^^2 •  CI3 = Gfl,^2 ' ^  +  2HC1  +  POCI3 ; 
and  a.H.O^.O    +  VC\,.C\,=  QJI,Q,.C\,  -f-  FQC],; 

whereas,  in  the  case  of  a  monobasic  acid,  the  action  consists 
of  one  stage  only.     This  difference  is  connected  by  Gerhardt 


CHLORIDES.  551 

with  the  fact,  that  a  bibasic  acid  may  be  supposed  to  contain 
water,  whereas  a  monobasic  acid  cannot  (p.  543).  According 
to  Williamson,  on  the  contrary,  the  two  stages  of  the  reaction, 
in  the  case  of  a  bibasic  acid,  are  precisely  similar  to  one 
another,  and  to  the  single  reaction  which  takes  place  wuth 
monobasic  acids.     Thus,  with  sulphuric  acid  — 

^2]o,  +  PGl^.  CI3  =  ^|]0  +  HCl  +  POCI3, 

and  hqI ]0  +  PCI2 .  CI3  =  SQ, .  Cl^  -f  HCl  +  POCla. 

The  difference  in  the  two  views  of  the  reaction  is  this:  —  that 
the  former  supposes  the  first  stage  of  the  action  to  consist  in 
the  formation  of  an  anhydrous  acid  ;  the  second  supposes  an 
intermediate  compound, —  a  chloro-hydrate  of  the  acid,  to  be 
produced.  The  formation  of  this  chloro-hydrate  has  been 
shown  by  Professor  Williamson  to  take  place  with  sulphuric 
acid.  If,  however,  one  of  the  two  molecules  of  hydrochloric 
acid  in  Gerhardt's  first  equation  be  supposed  to  remain  asso- 
ciated with  the  anhydrous  acid,  the  two  views  will  nearly 
coincide.  In  every  case,  indeed,  the  reaction  consists  essentially 
in  the  interchange  of  O  and  CI 3. 

The  triatomic  chlorides,  or  terchlorides,  contain,  within  two 
vapour  volumes,  three  atoms  of  chlorine  capable  of  forming  a 
metallic  chloride  when  acted  upon  by  the  mineral  alkalies. 

The  following  acid  chlorides  are  triatomic :  — 

Terchloride  of  phosphorus P.  CI3 

Chloride  of  phosphoryl  (oxychloride  of  phos- 
phorus     PO.CI3 

Chloride  of  sulphophosphoryl  (sulphochloride 

of  phosphorus) PS .  CI3 

Chloride  of  chlorophosphoryl  (pentachloride 

of  phosphorus) PCI  2 .  CI 3 

QQ  2 


552  HTDROCHLORIC    ACID   TYPE. 

Chloride  of  boron B  .  CI3 

Chloride  of  cy  anury  1  (solid  chloride  of  cyanogen)  Cy3 .  CI3 

The  BROMIDES,  IODIDES,  and  FLUORIDES,  are  exactly 
analogous  to  the  chlorides.  There  are  \ery  few  organic 
fluorides  known. 

The  CYANIDES  are  also  analogous  to  the  chlorides. 

The  metallic  cyanides  have  a  great  tendency  to  unite  and 

form  double  cyanides,  which  may  be  regarded  as  derivatives 

of  two  or  more  atoms  of  hydrochloric  acid.     Thus,  the  ferro- 

Fe  1 
cyanides  may  be  represented  by  the  formula  ^  i^y^y  ^^^^  the 

ferricyanides,    by  -^  ^  ]  Cyg ;  the  Fcg  in  the  latter  formula  being 

equivalent  to  H3. 

The  cyanides  of  the  alcohol-radicals  are  obtained  by  dis- 
tilling a  sulphovinate  or  homologous  salt  witli  cyanide  of 
potassium:  thus, — 

Kf£,H,^^2  +  KCy  =  *|^]©.  +  CA.Cy; 

or  by  the  action  of  anhydrous  phosphoric  acid  on  the  animon- 
iacal  salts  of  the  fatty  acids,  the  action  of  the  phosphoric  acid 
consisting  in  the  abstraction  of  water  :  thus, — 

^^ ■—"  Cyanide  of 

Acetate  of  methyl, 

ammonia. 

or,  generally, 

^°NH;'^^^  -  2H,a  =  CN.G„_,H,„.,. 

The  ammonia- salt  of  each  acid  in  the  series  yields  when  thus 
treated,  the  cyanide,  not  of  the  corresponding  alcohol-radical, 
but  of  the  next  lowest ;  thus :  the  propionate  yields  cyanide 
of  ethyl ;  the  acetate,  cyanide  of  methyl ;  and  the  formiate, 
cyanide  of  hydrogen,  or  hydrocyanic  acid. 


AMMONIA   TYPE.  553 

When  these  cyanides  are  heated  with  caustic  alkalies,  the 
opposite  change  takes  place ;  that  is  to  say,  an  alkaline  salt 
of  the  acid  corresponding  to  the  next  highest  alcohol  is  formed, 
and  ammonia  is  evolved :  thus, — 

CNH  +  ^]Q  +  H^    =      ^I^JO  +  NH, ; 


Cyanide 
of  hy 


Formiate  of 


drogen.  potash. 

Q^QU,  +  ]^]a  +  H.O    =      ^'^^IQ  +  NH3  ; 

Cyanide  of  " -^ — — ^ 

methyl.  Acetate  of 

potash. 

These  alcoholic  cyanides  may  also  be  regarded  as  nitriles : 

thus, — 


Cyanide 

Formo- 

Cyanide  of 

Aceto- 

of  hy- 

nitrile. 

methyl. 

nitrile 

drogen. 

generally :  GN  .  -GnHgn  +  ^   =   N  .  €„  +  ^  Hgn  + 1- 


AMMONIA   TYPE. 

Nitrides. — a.  Positive. — These  compounds  are  chiefly 
organic,  constituting  in  fact  the  organic  bases  or  alkaloids. 
A  few  mineral  nitrides  have,  however,  been  obtained  by  the 
action  of  ammonia  on  the  metals  or  their  oxides;  e.g.,  amide 
of  potassium,  N(H2K)  ;  nitride  of  potassium,  NK3 ;  nitride  of 
mercury  NHgg. 

The  primary  nitrides  of  the  alcohol-radicals,  such  as 
methylamine,  GH^N  =  N(GH3  .  Hj),  amylamine  -GsHjgN  = 

QQ  3 


554  AMMONIA   TYPE. 

N(C5Hii.  H2),  are  obtained : — 1.  By  the  action  of  the  bromides 
or  iodides  of  the  alcohol-radicals  on  ammonia  :  — 


£2  TJ 

NH3  +  Q,ll,l  =  HI   +    N  j      H 


Iodide  of  ethyl 


Ethylamine. 


2.  By  the  action  of  potash  on  the  cyanates  or  cyanurates  of 
the  same  radicals  : — 

Cyan  ate  of        Hydrate  of  Carbonate  of  ' ^ ^ 

ethyl.  potash.  potash.  Ethylamine. 

3.  By  the  action  of  reducing  agents,  such  as  hydrosulphuric 
acid,  or  acetate  of  iron,  on  certain  nitro-conjugated  hydro- 
carbons; thus: — 

■C  H 
^eH^CNO^)  +    3H„^  =  N^    h'+   2B^Q  +3^. 
. — —  (    H 

Nitrobenzol. 


Aniline  or 
phenylamine. 


They  are  also  frequently  produced  in  the  destructive  dis- 
tillation of  nitrogenised  organic  substances,  and  are  conse- 
quently found  in  coal-tar,  bone-oil,  &c. 

These  bodies  are  all  volatile  liquids,  having  more  or  less 
of  an  ammoniacal  odour.  The  bases  of  the  same  series — for 
instance,  those  formed  'from  the  alcohol-radicals  ^0^20+1  — 
are  less  volatile  and  more  oily,  as  they  contain  more  carbon. 
They  all  combine  with  acids  in  the  same  manner  as  ammonia, 
and  form  crystallisable  double  salts  with  bichloride  of  plati- 
num. Nitrous  acid  converts  them  into  alcohols  or  nitrous 
ethers,  with  elimination  of  nitrogen  :  — 

^2^5 )  1^  r:  XT 

H       N   +    Jj  ]  03  =  NN    +     ^^«  j  O2  +  H,0; 
H  '  .  _    ^  ^ 

"rrr ; — r"         Nitrous  acid.  Nitrite  of  ethyl. 

Ethylamnie. 


NITRIDES.  555 

A    h1  V^N^^3  =  2NN  +  2(^A|©)  +  H,©. 

"  .    .;7       ^  2  jnol.  hydrate 

^°^l^°e.  of  phenyl. 

Secondary  alcoholic  nitrides,  —  The  constitution  of  these 
bodies  maj  be  understood  from  the  following  examples : — 

p    TT 

Biethylamine,   QJIn^  .         .  =  -Q^hJ  N. 

H> 

Metethylamine,  ^gHgN  .         .  =  ^Hg^N. 

Ethaniline,  or  ethyphenylamine^CgHjjN  =  ^gHgVN. 

H  * 

They  are  obtained  by  the  action  of  the  bromides  or  iodides 
of  the  alcohol-radicals  on  the  primary  nitrides :  — 

Q2H5)  ^2^3) 

H  ^N  +  e^HgBr  =  QJiS  N  +  HBr. 
H>  H> 

Tertiary  alcoholic  nitrides,  or  nitrile  bases :  — 

Triethylamine,     •GgHigN    =  qIr,  In. 

€A  ) 

Biethamylamine  CqHo.N  =  ■Q2H5  f-N. 

Methamylaniline  G,»H,„N  =  GsH-.^N. 

These  compounds  are  formed  by  the  action  of  the  iodides 
and  bromides  of  the  alcohol-radicals  on  the  secondary  alco- 
holic nitrides  ;  also  by  the  distillation  of  the  ammonium-bases, 
thus : — 

Q  Q  4 


556  AMMONIA  TYPE. 

N(€A),^  O  =  (^H^yj  +  G,H,   +  H,a. 

"^ — zi~y 7^  Triethylamine.      Ethylene. 

Hydrate  of 

tetrethylium. 

Triethylamine  is  likewise  obtained  by  the  action  of  ethylate 
of  potassium  on  cyanate  of  ethyl :  — 

"t: ' ■'  ^ :;<- — ^  „  "X^^" '  Triethylamine. 

Cyanate  of  2  at.  ethylate  of  Carbonate 

ethyl.  potassium.  of  potash. 

This  action  is  analogous  to  that  of  hydrate  of  potash  or 
cyanate  of  ethyl  (p.  554).  The  other  tertiary  alcoholic 
nitrides  might  doubtless  be  obtained  in  a  similar  manner. 

There   are   also    nitrides    containing   conjugated    alcohol - 
radicals;  e.g. 


Bichlorethylamine  esH^Cl^N 

H       ) 

Chloraniline         .  G,H„C1N 

=  H  tN. 
H      S 

Nitraniline  .    .     .  €eHe(NO,)N 

CoH,(N©,) 
H 

h- 


Nitrides  of  aldehyde- radicals.  —  These  bodies  are  but  little 
known. 

Acetosylamine,  N(H2 .  -^2^3)^  ^^  obtained  by  the  action  of 
ammonia  on  chloride  of  ethylene  (chloride  of  acetosyl  and 
hydrogen) :  — 

H'i^^2  +  2NH3  =       'h|n.HC1 +NH,C1. 


•G-oH, 


Chloride  of  aceto- 
syl and  hydrogen.  Hydrochlorate  of 

acetosylamine. 


AMIDES.  557 

The  natural  vegeto-alkalies,  morphine,  strychnine,  &c.,  are 
most  probably  of  similar  nature  to  these  artificial  alkalies, 
but  they  have  not  yet  been  reduced  to  regular  series. 

h.  Negative  or  acid  nitrides.  —  These  are  the  compounds 
generally  called  amides. 

Primary  amides. — In  these  compounds,  one-third  of  the  hy- 
drogen in  1,  2,  or  3  molecules  of  ammonia  is  replaced  by  an 
acid  radical. 


a.  Monatomic 


e^HgO 


Acetamide,  or   nitride   of  acetyl  ^^^ir"  tr  isj£i_Tyj)    ^u 
hydrogen j         ^  iH 

Butyramide,  or  nitride  of  butyryl  and?^^  -rr  fjn—isjj    \t^ 
hydrogen (     H 

p    TT   Q 

Benzamide,  or  nitride  of  benzoyl  ^^^^n  TT  l^JiH— "\r\    Vr^ 
hydrogen 5    v    7  <     H    * 

These  amides  differ  from  the  corresponding  ammoniacal  salts 
by  the  elements  of  one  atom  of  water :  — 

NH4   ^^        y±2^-^i     JJ2     • 

Acetate  of  ammonia.  Acetamide. 

They  are  produced  by  the  action  of  ammonia  on  the  anhy- 
drous acids:  — 

1^  +  NH3  =  ^1=^  +  N[^|^; 

Benzoic  anhydride.  Benzoic  acid.  Benzamide. 

by  the  action  of  ammonia  on  the  acid  chlorides :  — 
^yH^O-Cl  +  NH3  =  HCl  +  NJ^^H^O. 
and  by  the  action  of  ammonia  on  the  compound  ethers :  — 


558  AMMONIA   TYPE. 

%H^^]0  +  NH3  =  \H.j^  ^  NJ^I^O 

Acetate  of  ethyl.  Alcohol. 

These  amides  are  neutral  crystalline  bodies,  which,  when 
boiled  with  aqueous  acids  or  alkalies,  take  up  water,  and  are 
converted  into  ammonia-salts.  When  treated  with  anhydrous 
phosphoric  acid,  they  give  up  the  elements  of  1  at.  water,  and 
are  converted  into  cyanides  of  the  alcohol  radicals :  — 


^- r-~ — '  Cyanide  of  methyl. 

Acetamide. 

/3.  Biatomic.     Primary  biamides  or  diamides : — 


Oxamide,  or  nitride  of  oxalyl  and)^^  TT  "NT  jQ  —  TsT  <  TT 
hydrogen ^2422        ^(jj 


■^Ttj'T^n 


2 
2 


[GO 


Succinamide,  or  nitride  of  succinvl)  r^  tt  at  /-k      xt  1    ^tt'* 
and  hydrogen )  ^     H 

Urea  and  carbamide,  or  nitride  ofj^^Tj  -m-  ri   —  "Nr  i  TT 
carbonyl  and  hydrogen      .     .     . )        ^    ^  ^  (  jj 

Tartramide,    or   nitride  of  tartryl  >  ^  tt  7^- p.  _  isj  j     w 
and  hydrogen Jt,,H,WM-^.|     H, 

They  are   produced   by  the  action  of  heat  on  the  neutral 
ammonia-salts  of  bibasic  acids  :  — 


Oxalate  of 
ammonia. 

by  the  combination  of  ammonia  with  secondary  amides :  — 

N{^  +  NH3  =  nJ  H,; 

« — , — '  >^  Hg 

Cyanic  acid <--, — ' 

or  cai'bonimide.  Urea. 


AMIDES.  559 

and  by  the  action  of  ammonia  on  compound  ethers  or  acid 
chlorides : — 

(^^+ 2NH3  =  (ej^^ja,  +  n£|^^ 

Oxalate  of  ethyl.  2  at.  alcohol.  Oxamide. 

^.H.a^.CI^    +    2NH3  =  2HC1    +  Nj^^^*^^ 


Chloride  of 


H4 


succinyl.  Succinamide. 

y. — Triatomic.      Primary  triamides : — 
Triphosphamide,   or   nitride   of^  rPO 


phosphoryl  and  hydrogen 


:  1 ".  ih 


Citramide,  or  nitride  of  citrjl^  N  O  =N  J^e^sO^ 

and  hydrogen j      6    11    3    4        ^i      Hg 

Melamine  and  melam,  or  nitride )  ^  tt  ^y  -^  ^  Cy 

of  cyanuryl  and  hydro^ren      J      3    6    6     —       ^  i  jj 


jyanuryl  and  hydrogei 

Secondary  amides. — In  these  compounds,  two-thirds  of  the 
hydrogen  in  a  molecule  of  ammonia  are  replaced  by  acid 
radicals,  viz. : 

1.  By  two  monatomic  radicals  ;   e.g.i  — 

Nitride   of  bisulphophenyh^  ^  ^&^l 

and  hydrogen  .     .     .     .)     *^    "      ^    *  '       H 

Nitride   of    sulphophenyl,  J^.^H^NSA  =  nJ  efll^' 
benzoyl,  and  hydrogen  J     ^^    ^^       ^    ^  '        H 

These  amides  are  produced  by  the  action  of  acid  chlorides 
on  the  primary  amides  or  their  metallic  salts. 


Ni 


'^6-*^5^^2  ^  ^A-tl.'i'^'^o 


,      H        4  aH,O.Cl  =  N^  ^.H^O  +  HCI. 
^      H  ^       H 


2.  The  two  atoms  of  hydrogen  are  replaced  by  one  molecule 
of  a  biatomic  radical.     These  compounds  are  called  imides. 


560  AMMONIA   TYPE. 

Carbon  imide  (cyanic  acid)or  nitrides  rCO 

of  carbonyl  and  hydrogen     .     .  I  ~     ^    H 

Succinimide,  or  nitride  of  succinyU      ^  ^^  ^^.^^H^O,. 
and  hydrogen J    4    s       2        I      jj 

Most  of  them  are  produced  by  the  action  of  heat  on  the 
acid  ammoniacal  salts  of  bibasic  acids,  the  change  consisting 
in  the  elimination  of  2  molecules  of  water :  — 

H      fa,  -  2H,0  =  l<f{'^*^^>' 


NH, 

Acid  succinate  of 
ammonia. 


Succinimide. 


by  the  action  of  heat  on  the  biamides  of  bibasic  acids,  ammonia 
being  then  given  off: — 

(G4H4O2  f/2  TT  jQ 

nJ      H,     -     NH3     =     N  p^ti^^^ 

Succinamide.  Succinimide. 


or  by  the  action  of  heat  on  the  amidogen  acids. 

Tertiary  Amides. — In  these  compounds,  all  the  hydrogen  in 
ammonia  is  replaced  by  acid  radicals. 

a.  Monatomic. — 1.    The   hydrogen   is   replaced   by   three 
monatomic  radicals  ;   e.g.: — 

rCeH,SO, 
Nitride  of  sulphophenyl,  benzoyl,  and  acetyl      .  NJ-G^HsO 

Nitride  of  sulphophenyl  and  benzoyl  ....   N-^G^HsO 

2.  One  atom  of  hydrogen  is  replaced  by  a  monatomic,  and 
the  other  two  by  a  biatomic  radical ; — 

jC  TT  O 

Nitride  of  succinyl  and  sulphophenyl  .     .  ^{ri''H^S.(4 


INTERMEDIATE   NITRIDES.  561 

These  amides  are  formed  by  the  action  of  acid  chlorides  on 
the  secondary  amides  or  their  silver-salts. 

3.  All  the  hydrogen  is  replaced  by  a  triatomic  radical. 
The  composition  of  several  inorganic  compounds  may  be  ex- 
pressed in  this  manner  : — 

Monophosphamide,  or  nitride  of  phosphoryl       =  N  .  PO. 

Boramide,  or  nitride  of  boron      ....        =         N  .  B. 

Free  nitrogen,  or  nitride  of  nitrogen,  the  ^        __  at    iv 

amide  of  nitrous  acid 

Protoxide  of  nitrogen,  or  nitride  of  azo-^ 
tyl,  the  amide  of  nitric  acid     ... 

/3.  Biatomic. — Compounds  in  which  all  the  hydrogen  of 
2  molecules  of  ammonia  is  replaced  by  monatomic  or  biatomic 
radicals  : — 

Trisuccinamide,  or  biamide  of  trisuccinyl      .   N9^■G4H402 

Biamide  of  succinyl,  bibenzoyl,   and  bi->      -kt  S^A  Ac 
sulphophenyl j   .  IN  2 1(^7^5^ 


These  tertiary  hiamides  are  produced  by  the  action  of  acid 
chlorides  on  other  amides  or  biamides. 

Intermediate  nitrides,  or  amidog en- salts, — These  are  com- 
pounds in  which  the  hydrogen  of  ammonia  is  replaced  partly 
by  a  basic,  partly  by  an  acid  radical.  Most  of  the  primary 
and  secondary-  amides  form  such  salts,  which  are  produced  by 
the  direct  action  of  the  amides  on  the  corresponding  oxides  or 
their  salts  ;  e.  g.i — 

Benzamidate  of  mercury       .     .     .     •  Nj      Hg 

When  the  positive  radical  is  an  alcohol-radical,  the  com- 
pounds are  called  alcalamides ;  those  which  contain  phenyl, 
•GgHfi,  are  also  called  anilides :  thus, — 


562  AMMONIA   TYPE. 


^«H^ 


Phenjl-acetamide  or  acetanilide     .     .  Nj^gHgO 

^     H 

Ethyl-cyanamide N)  Cy. 

I  H 
Phosphides. — These  compounds  are  derived  from  the  type 
ammonia  by  the  substitution  of  phosphorus  for  nitrogen,  and 
of  various  radicals  for  the  hydrogen.  Phosphuretted  hydro- 
gen, PHg,  is  analogous  to  ammonia,  and  forms  with  hydriodic 
acid  a  compound,  PH3 .  HI,  or  PH^I,  which  crystallises  in 
cubes  like  iodide  of  ammonium,  or  iodide  of  potassium. 

With  the  alcohol-radicals,  phosphorus  forms  compounds 
analogous  to  the  alcoholic  nitrides,  and  like  those  bodies  pos- 
sessing alkaline  properties  ;  e.  g.,  triphosphomethylamine,  or 
trimethyphosphine,  V{Gil^y  These  compounds  may  be 
obtained  by  the  action  of  terchloride  of  phosphorus  on  zinc- 
methyl,  zinc-ethyl,  &c.,  the  reaction  being  expressed  by  the 
following  general  equation  : — 

PCig  -f  34;„H2n  +  iZn  =  3ZnCl  +  PC^nH^n  +  Og. 

These  phosphides,  treated  with  the  iodides  of  the  corre- 
sponding alcohol-radicals,  yield  compounds  analogous  to  the 
ammonium  bases  :  thus, — 

P(eH,)3  +  CAi  =  gg3),^P.i. 

The  only  negative  or  acid  phosphide  known  is  chloracety- 
phide,  or  phosphide  of  terchloracetyl  =  V{Qr^Q\^Q- .  H  .  H). 

Arsenides  and  Antimonides.— Arsenic  and  antimony 
also  form  compounds  of  the  ammonia  type;  e.  g.,  AsHg;  SbHg; 
As(-G2H5)3 ;  S^-GgHg) ;  but  the  arsenides  and  antimonides 
of  the  alcohol-radicals  differ  considerably  in  their  properties 
from  the  nitrides  and  phosphides,  not  combining  with  hydro- 
chloric acid,  &c.,  in  the  same  manner  as  ammonia,  but  rather 
combining  with  oxygen,  chlorine,  iodine,  &c.,  like  metals. 
They  belong,  therefore,  rather  to  the  hydrogen  type  (p.  567). 


HYDROGEN  TYPE.  563 


HYDROGEN  TYPE. 


The  primary  derivatives  of  this  type  are :  — 

1.  The  hydrides  of  the  metals  proper,  A  small  number 
only  of  these  are  known,  viz.,  CugH,  AsHg,  and  SbHg.  The 
two  latter  may  also  be  regarded  as  derivatives  of  ammonia. 

2.  The  hydrides  of  the  alcohol-radicals,  Q'Jl2n-\-\i  viz., 
marsh-gas,  or  hydride  of  methyl,  GrYi^  =  H  .  -GHg ;  hydride  of 
ethyl,  e,H,=  H.e,H,;hjdrideofan.yl,e,H„=  H.C,H„, 
&c.  These  compounds  are  formed  by  the  action  of  zinc  on  the 
chlorides  or  iodides  of  the  corresponding  alcohol-radicals  :  — 

2Gr^Yi,\   +  Zn  Zn  =  2ZnI  +  H.e^H^  +  ^gH^; 

Iodide  of  Hydride  of       Ethylene, 

ethyl.  ethyl. 

also  by  the  action  of  water  on  zinc-methyl,  zinc- ethyl,  &c. :  — 

Zn.G,H,  +  giO  =  H.e,H,  +  |"}0; 

occasionally  also  in  the  destructive  distillation  or  spontaneous 
decomposition  of  vegetable  and  animal  substances.  Marsh- 
gas,  for  example,  is  formed  by  the  putrefaction  of  vegetable 
matter  under  water  (I.  375).  The  hydrides  of  methyl  and 
ethyl  are  gaseous  at  ordinary  temperatures,  the  rest  are 
liquid  or  solid.  They  are  decomposed  by  chlorine,  with  form- 
ation of  substitution-products  ;  thus  — 

H.^^H,  +  ClCl  =  H.€2(H,CI)  +  HCl. 

There  are  likewise  hydrides  of  alcohol-radicals  of  the 
form  H.-GnH2n-75  the  best  known  of  which  is  benzol,  or 
hydride  of  phenyl,  -GgHg  or  H .  ^^gH^.  These  compounds 
are  obtained  in  the  destructive  distillation  of  many  organic 
substances ;  benzol,  for  instance,  by  the  distillation  of  coal. 
They  are  also  formed  by  the  dry  distillation  of  the  monobasic 


564  HYDROGEN    TYPE. 

acids  ^nHga-gO,  with  excess  of  lime  or  baryta,  a  carbonate 
of  the  base  being  formed  at  the  same  time :  — 

Benzoic  Acid.  Benzol. 

3.  The  hydrides  of  the  aldehyde- radicals,  Q^  Hgn-i.  These 
are :  — 

Ethylene,  olefiant  gas,  or  hydride  of  acetosyl  ^2^4  =  ^  •  "^2^3 
Propylene,  or  hydride  of  propionyl  .  .  .  Q^11q  =  II  .Q^H^ 
Butylene,  or  hydride  of  butyryl  ....  QJl^  =  ll.QJij 
Amy lene,  or  hydride  of  valeryl     .     .     .       ■G5Hjo  =  H. -GgHg 

These  compounds  might  also  be  regarded  as  hydrides  of 
the  alcohol-radicals  -GnH^n-i;  for  example,  propylene  as 
hydride  of  allyl  (p.  532).  Possibly,  however,  there  may  be 
two  isomeric  series  of  these  compounds,  the  one  derived  from 
the  alcohols,  the  other  from  the  aldehydes. 

These  hydro- carbons  are  formed  by  the  destructive  dis- 
tillation of  organic  substances,  several  of  them  being  found 
among  the  products  of  the  distillation  of  coal.  They  are 
also  produced  by  the  action  of  strong  sulphuric  acid  at  a  high 
temperature  on  the  alcohols,  the  change  consisting  in  the 
abstraction  of  the  elements  of  water  :  thus  :  — 

Alcohol.  Ethylene. 

The  only  body  of  the  series  which  is  gaseous  at  ordinary 
temperatures  is  ethylene  (L  384) ;  the  rest  are  liquid  or 
solid.  The  first  term,  methylene,  has  not  been  obtained  in 
the  free  state.  These  compounds  are  especially  distinguished 
by  combining  with  two  atoms  of  chlorine,  bromine,  &c., 
forming  compounds  homologous  with  Dutch  liquid  or  chloride 
of  ethylene,  -GgH^ ,  C\^ ;  whereas  the  hydrides  of  the  radicals 
•G„H.2n  + 1  are  decomposed  by  chlorine. 

The  lower  compounds  of  the  series  also  combine  with  an- 
hydrous sulphuric  acid.     Thus,  olefiant  gas   is  immediately 


HYDRIDES   or   ACIDS.  5Q5 

absorbed  by  the  anhydrous  acid,  or  by  a  coke  ball  soaked  in 
fuming  oil  of  vitriol.  This  property,  and  that  of  forming  liquid 
compounds  with  chlorine  and  bromine,  is  made  available  for 
separating  olefiant  gas,  and  the  other  more  volatile  hydro- 
carbons of  the  series,  from  gaseous  mixtures. 

4.  The  hydrides  of  the  acid  radicals. 

a.  Monatomic.  —  The  hydrides  of  the  acid  radicals 
^nH2u_iO,  are  evidently  the  aldehydes  of  the  fatty  acids 
(p.  535):  thus:  — 

Acetic  aldehyde  =  H .  ^^HOg  =  ^^gs  jo 

Butyric  aldehyde         =  H .  ^.H^O  =  ^^^^JO 

Benzoic  aldehyde       .^  ^  ^rH^O  j^ 

(bitter  almond  oil))  ^    ^  H     ^ 

The  following  compounds  may  be  regarded  as  the  alde- 
hydes of  monobasic  mineral  acids ;  that  is  to  say,  as  the 
hydrides  of  the  radicals  contained  in  those  acids  considered 
as  derivatives  of  water :  — 

Nitrous  acid,  or  aldehyde  of  nitric  acid  NHOg  =  H  .  NO2 

Hydrochloric  acid,  or  aldehyde  of  hypo- 
chlorous  acid CIH      =  H .  CI 

Hydrocyanic  acid,  or  aldehyde  of  cyanic 

acid \     ,     .     .       €HN  =  H.Cy 

Spontaneously  inflammable  phosphuret- 
ted  hydrogen,  or  aldehyde  of  hy pophos- 
phorous  acid PH       =  H  .  P 

/3.  Hydrides  of  biatomic  acid  radicals  :  — 
Hydrosulphuric    acid,   or   aldehyde    of 

hyposulphurous  acid -S-Hg     =  Hg .  S 

Hydroselenic   acid,  or  aldehyde  of  liy- 

poselenlous  acid -S-eHg  =  Hg .  Se 

V  .  VOL.  XI.    .  it.R     ... 


566  ALCOHOL   METALS. 

y  Hydrides  of  triatomic  acid  radicals :  — 

Non-spontaneouslj  inflammable  phosphu- 
retted  hydrogen,  or  aldehyde  of  phos- 
phorous acid PH3    =  H3 .  P 

Antimoniuretted  hydrogen,  or  aldehyde  of 

antimonious  acid SbHg  =  Hg .  Sb 

The  secondary  derivatives  of  the  hydrogen-type  are  — 

1.  The  ordinary  metals: — Potassium,  KK,  derived  from 
HH ;  antimony,  SbSb,  derived  from  H3H3 ;  aluminium, 
AlgAlg,  derived  from  H3H3,  &c. 

2.  The  alcoliol-metahi  derived  from  the  type  HH,  both 
atoms  of  hydrogen  being  replaced  by  alcohol  radicals.  The 
only  bodies  of  this  class  which  have  yet  been  obtained  are 
those  containing  the  radicals  -GnHan+i;  viz.  (a.)  Those  in 
which  the  two  atoms  of  hydrogen  are  replaced  by  the  same 
radical :  methyl,  ^Hg .  ^Hg ;  ethyl,  ^^^s  •  "^2-^5  >  i>utyl  or 
tetryl,  JQ4H9  .  •G4H9 ;  amyl,  ^5-^11  •  ^s^n »  Cf^P'^^oyl  or  hexyl, 
•GgHjg .  -GgHjg ;  and  capryl  or  octyl,  ^gHj^ .  -GgHj^. — (6.)  Those 
in  which  the  two  atoms  of  hydrogen  are  replaced  by  different 
radicals :  ethylo-butyl,  ethyl-amyl,  methylo-caproyl,  butyl-amyl, 
and  butylo-caproyl.  The  reasons  for  representing  the  bodies 
of  the  class  (a.)  in  the  free  state,  by  the  double  formulae,  have 
been  already  given  (p.  518). 

These  alcohol-metals  are  obtained  by  the  action  of  zinc  on 
the  iodides  of  the  alcohol-radicals  (p.  531);  by  the  action  of 
sodium  on  the  chlorides  of  the  same  radicals;  and  by  the 
electrolysis  of  the  alkaline  salts  of  the  fatty  acids,  carbonic 
acid  and  hydrogen  being  evolved  at  the  same  time :  — 

2  (^^-^g^ja)  +  H,a  =  (^Hg),  +  H,  +f^2  +  ^J^r 

Acetate  of  potash.  Methyl.  of^PoS? 

The  alcohol-metals,  containing  two  different  radicals,  are 


MIXED   METALS.  567 

obtained  by  the  action  of  sodium  on  a  mixture  of  the  corre- 
sponding iodides  :  thus,  with  the  iodides  of  ethyl  and  butyl — 

e^H.I  +  Na  Na   =  Nal  +  Na^^H, 
and  Qfi,l  +  Na^^H^  =  Nal  +  QJI,.QJi,; 

also,  by  the  electrolysis  of  a  mixture  of  the  alkaline  salts  of 
two  of  the  fatty  acids. 

Methyl  and  ethyl  are  gaseous  at  ordinary  temperatures ; 
the  other  alcohol-metals  are  liquids  more  or  less  volatile. 
They  exhibit  but  little  tendency  to  unite  with  other  bodies. 
The  alcohols  and  ethers  cannot  be  formed  from  them  directly. 
Oxygen  and  sulphur  do  not  act  upon  them,  and  chlorine  and 
bromine  do  not  unite  with  them,  but  decompose  them,  form- 
ing substitution-products;  they  are  not  attacked  by  hydro- 
chloric acid  or  by  potash.  For  their  boiling  points  and 
vapour-densities,  see  page  518. 

3.  Mixed  metals,  containing  a  metal  proper  and  an  alcohol- 
radical;  e.g.  zinc-methyl,  GH^.Zn;  zinc-ethyl,  Q^H^.Zn;  zinc- 
amy  I,  CgHj^Zn;  stannethyl,  -GgH^Sn;  arsenethyl,  (^2^5)3  As; 
stihmethyl,  (CH3)Sb,  &c. 

These  compounds  are  obtained  by  the  action  of  iodide  of 
ethyl,  &c.,  on  the  corresponding  metals,  or  their  alloys  with 
potassium  or  sodium ;  thus,  the  compounds  of  ethyl  and  ar- 
senic are  obtained  by  distilling  iodide  of  ethyl  with  arsenide 
of  sodium ;  arsen-bimethyl  or  cacodyl,  (GH3)2As,  is  likewise 
produced  by  the  dry  distillation  of  a  mixture  of  acetate  of 
soda  and  arsenious  acid.  To  understand  this  reaction,  it  must 
be  remembered  that  the  radical  of  acetic  acid,  ^gHgO,  may  be 
supposed  to  consist  of  QQ-  conjugated  with  methyl,  -GHg  : — 

Acetate  of  soda.  Oxide  of  cacodyl. 

These  compounds  are  liquids  more  or  less  volatile,  and 

B  R  2 


568  CONJUGATE  METALS. 

generally  having  a  very  offensive  odour ;  they  oxidise  rapidly 
in  the  air,  and  sometimes  take  fire.  Zinc-methyl,  zinc-ethyl, 
and  cacodyl  take  fire  instantly  on  coming  in  contact  with 
the  air. 

Zinc-methyl,  zinc-ethyl,  and  zinc-amyl  differ  in  some  re- 
spects from  the  other  mixed  metals  in  their  behaviour  with 
oxygen,  sulphur,  chlorine,  iodine,  &c.  When  these  metals 
are  exposed  to  the  air,  but  not  freely  enough  to  cause  them 
to  take  fire,  they  are  converted  into  mixed  ethers ;  thus, — 

2  (^Hg. Zn)  +  oa  ==  2  (^^^i a). 

Similarly  with  sulphur.  Chlorine,  bromine,  and  iodine,  on 
the  other  hand,  decompose  them,  producing  a  chloride  of  the 
metal  and  a  chloride  of  the  alcohol-radical :  — 

^Hg.  Zn  +  ClCl  =  ^Hg.  CI  +  ZnCl. 

This  difference  of  reaction  is  in  perfect  accordance  with  the 
bibasic  character  of  oxygen  and  sulphur,  and  the  monobasic 
character  of  chlorine,  bromine,  and  iodine  (compare  pp.  515, 
547).  The  same  mixed  metals  decompose  water,  forming  a 
hydrate  of  zinc  and  a  hydride  of  the  alcohol-radical;  — 

^HgZn  +  ][^]  O  ==  H .  ^Hg  -f-  ^^]0. 

The  other  mixed  metals — thence  called  conjugate  metals — 
containing  tin,  antimony,  arsenic,  bismuth,  lead,  and  mercury, 
combine  as  simple  radicals  with  oxygen,  chlorine,  &c.,  form- 
ing oxides,  chlorides,  &c.  The  oxides  of  these  conjugate 
metals  may  be  regarded  as  derivatives  of  the  oxides  of  the 
simple  metals  contained  in  them,  one  or  more  atoms  of  oxygen 
being  replaced  by  its  equivalent  quantity  of  ethyl,  &;c. ;  that 
is,  O  by  (■€•2115)2,  &c.  This  will  be  seen  from  the  following 
table,  in  which  the  symbol  Et  stands  for  (^2^5)2  •  — 


CONJUGATE   METALS.  569 

Type.  Derivative. 

Arsenious  acid,  ASgOg .  Oxide  of  arsen-biethyl      As2(Et20)  =  0  j  jt^sCG^U) 

Arsenic  acid,  AsjOg  .  .  Oxide  of  arsen-triethyl  AsaCEtaOj)  =  O2 1  ^3^^=^ jjy 

Arsenic  acid,  As^Q^ . .  Oxide  of  arsenethylium    As^(Et^Q■)=^\  As(cV) 

Stannic  oxide,  SngO^  .  Oxide  of  stannethyl  SuaCEtO) =0 1  gn/^-^H^ 

Stannic  oxide  (2  at.),  1 /-w  -a      eo    .        *i,  1        d    /tti*  r»N     r\    fSnoCOaH-), 
Sn,0,  ....\./:)  Oxide  of  5-stannethyl       Sn,(Et3O)=02|sn2(GX)3 

Me^c^uncoxide(2at.),|Q^.^^  of--«-ethyl       Hg,(EtO) ^. O^ { g jgg^j 

The  method  of  determining  the  equivalent  in  hydrogen  of 
these  conjugate  radicals  has  been  already  explained  (p.  526). 

Acid  metals,  or  metalloids. — These  are  the  elements  com- 
monly called  negative  or  chlorous :  e.  g.  oxygen,  sulphur, 
phosphorus,  &c. 


RELATIONS   BETWEEN   CHEMICAL   COMPOSI- 
TION AND  DENSITY. 

Atomic  Volume  of  Liquids  * — The  atomic  volumes  of  bodies 

are  the  spaces  occupied  by  quantities  proportional  to  their 

atomic  v^eights,  and  are  calculated  by  dividing  the  atomic 

weights  by  the  specific  gravities  (I.  210);  thus,  the  atomic 

weights  of  copper  and  silver  being,  on  the  hydrogen  scale, 

31*7  and  108*1,  and  their  specific  gravities  (water  =1)  being 

31*7 

8-93  and  10*57,  their  atomic  volumes  are,  respectively, 

8*93 

*  H.  Kopp,  Ann.  Ch.  Pharm.  xcvi.  2,  330. 
H  R  3 


570  ATOMIC   VOLUME   OF   LIQUIDS. 

and  r ,  or  3*6  and  10-2.     These  numbers  are.  of  course, 

1057 

only  relative;    their  actual  values  depend  en  the  units  of 

atomic  volume  and  density  adopted. 

It  has  already  been  observed,  that  the  relations  between 
atomic  weight  and  density  are  much  less  simple  in  solids  and 
liquids  than  in  gases,  the  diversities  in  the  rates  of  expansion 
by  heat  of  liquid  and  solid  bodies  being  alone  sufficient  to 
complicate  these  relations  to  a  considerable  extent.  With 
regard  to  liquids  in  particular,  the  researches  of  Professor 
Kopp  have  shown  that  their  atomic  volumes  are  comparable 
only  at  temperatures  for  which  the  tensions  of  the  vapours 
are  equal ;  for  example,  at  the  boiling  points  of  the  liquids. 
If  the  atomic  weights  of  liquids  are  compared  with  their  den- 
sities at  equal  temperatures,  no  regular  relations  can  be  per- 
ceived ;  but  when  the  same  comparison  is  made  at  the  boiling 
temperatures  of  the  respective  liquids,  several  remarkable 
laws  become  apparent.  The  density  of  a  liquid  at  its  boiling 
point  cannot  be  ascertained  by  direct  experiment ;  but  when 
the  density  at  any  one  point,  say  at  15*5°  C.  (60°  F.),  has  been 
ascertained,  and  the  rate  of  expansion  is  also  known,  the 
density  at  the  boiling  point  may  be  calculated.  Abundant 
data  for  these  calculations  are  supplied  by  the  labours  of 
Kopp  and  Pierre  (II.  433). 

The  following  table  contains  Kopp's  determinations  of  the 
atomic  volumes  of  a  considerable  number  of  liquids  contain- 
ing carbon,  hydrogen,  and  oxygen  at  their  boiling  points. 
The  atomic  weights  are  those  of  the  hydrogen-scale.  The 
calculated  atomic  volumes  in  the  fourth  column  are  deter- 
mined by  a  method  to  be  presently  described;  the  observed 
atomic  volumes  in  the  fifth  column  are  the  quotients  of  the 
atomic  weights,  on  the  hydrogen-scale,  divided  by  the  specific 
gravities  referred  to  water  as  unity. 


ATOMIC   VOLUME   OF   LIQUIDS. 


571 


Table  A. 
Atomic  Volumes  of  Liquids  containing  Carbon,  Hydrogen,  and  Oxygen. 


Atomic  Volume  at  the  Boiling  Point. 

Substance. 

Formula. 

Atomic 
Weight. 

Calculated. 

Observed. 

/  Benzol 

GeH, 

78 

99-0 

96-0...  99-7  at    80° 

Cymol 

134 

187-0 

183-5. ..185-2  „ 

175 

^  \  Naphthalia    . 
S  ^Aldehyde      . 
"Z  <  Valeraldehyde       . 

128 

1540 

149-2     .      .     „ 

218 

0,HA 

44 

56-2 

56-0...  56-9  , 

21 

O.H.oO, 

86 

122-2 

117  3.. .120-3  „ 

101 

^  1  Bitter  almond  oil  . 

G.HgO 

106 

122-2 

118-4     .      .     , 

179 

H  /  Cuminol 

O.oHeO 

148 

188-2 

189-2     .      .     , 

236 

1  Butyl    .... 

^sH.e 

114 

187-0 

184-5. ..186-8  , 

108 

\  Acetone 

0,H,0 

58 

78-2 

77-3...  77-6  , 

56 

"Water  .  •       . 

HoO 

18 

18-8 

18-8     .      .     , 

100 

Wood-spirit  . 

€H,0 

32 

40-8 

41-9...   42-2  , 

59 

Alcohol 

O^HgO 

46 

62-8 

61-8...   62-5  , 

78 

Amylic  alcohol 

0,H,,0 

88 

128-8 

123  6.. .124-4  , 

135 

Phenylic  alcohol    . 

^eHeO 

94 

106-8 

103-6.. .104-0  , 

194 

Benzoic  alcohol     , 

G.HgO 

108 

128-8 

123-7     .      .     „ 

213 

Formic  acid  . 

0H,0, 

46 

420 

40-9...  41-8  , 

99 

Acetic  acid   . 

e,H,o, 

60 

64-0 

63-5...   63-8  , 

,  118 

Propionic  acid 

G^HgO, 

74 

86-0 

85-4     .       .     , 

137 

Butyric  acid 

e^HA 

88 

108-0 

106-4.. .107-8  , 

156 

Valerianic  acid 

^5H,o02 

102 

130-0 

130-2. ..131-2  , 

175 

Benzoic  acid 

^tH^O^ 

122 

130-0 

126-9     .       .     , 

253 

Vinic  ether    . 

e,H,„& 

74 

106-8 

105-6... 106-4  , 

34 

O 

Acetic  acid  (anhydrous) 

G,H,03 

102 

109-2 

109-9. ..110-1  , 

138 

a 

Formiate  of  methyl 

G,H,0, 

60 

640 

63-4     .      .     „ 

36 

w^ 

Acetate  of  methyl 

0,H,0, 

74 

86-0 

83-7...   85-8  , 

55 

a 

Formiate  of  ethyl . 

G3H,0, 

74 

86-0 

84-9...  85-7  , 

55 

^ 

Acetate  of  ethyl    . 

e.H^o, 

88 

108-0 

107-4. ..107-8  , 

74 

Butyrate  of  methyl 

e5HioO, 

102 

130-0 

125-7... 127-3  , 

93 

Propionate  of  ethyl 

e^H.oO, 

102 

130-0 

125-8     .      .     , 

93 

Valerate  of  methyl 

^eH.A 

116 

152-0 

148-7... 149-6  , 

112 

Butyrate  of  ethyl  . 

G.H.A 

116 

1520 

149-1. ..149-4  , 

112' 

Acetate  of  butyl    . 

G,H„0, 

116 

1520 

149-3     .      .     , 

112 

Formiate  of  amyl  . 

0,Hj,0, 

116 

152-0 

149-4...  150-2  , 

112 

Valerate  of  ethyl   . 

e,H„o, 

130 

174-0 

173-5. ..173-6  , 

131 

Acetate  of  amyl    . 

0,H.A 

130 

174-0 

173-3. ..175-5  , 

131 

Valerate  of  amyl  . 

^lo^ao^a 

172 

240-0 

244-1     .      .     , 

188 

Benzoate  of  methyl 

G,H,^, 

136 

152-0 

148-5.. .150-3  „ 

190 

Benzoate  of  ethyl  . 

e.H^O, 

150 

174-0 

172-4... 174-8  , 

209 

Benzoate  of  amyl  . 

e„H„0, 

192 

240-0 

247-7     .      .     , 

266 

^Cinnamate  of  ethyl 

^uH.A 

176 

207-0 

211-3     .      .     „ 

260 

<^  /Acid  salicylate  of  methyl 

e^H.Og 

152 

159-8 

156-2.. .157-0  , 

223 

a  ^  Carbonate  of  ethyl 

e^H.oOa 

118 

137-8 

138-8.. .139-4  „ 

126 

S  ;  Oxalate  of  methyl 

O.H^O, 

118 

117-0 

116-3     .      .     „ 

162 

^     Oxalate  of  ethyl    . 
Qh  \  Succinate  of  ethyl 

e6H,o^4 

146 

161-0 

166-8. ..167-1  „ 

186 

^bHmO. 

174 

205-0 

209-0     .      .     „ 

217 

R  E  4 


5-72  ATOMIC    VOLUME   OF    LIQUIDS. 

A  comparison  of  the  numbers  in  this  table  leads  to  the 
following  remarkable  results  :  — 

\»  Differences  of  atomic  volume  are  in  numerous  instances 
proportional  to  the  differences  between  the  corresponding  chemical 
formuke. — Thus  liquids,  whose  formulae  differ  by  n .  -GHg,  differ 
in  atomic  volume  by  n .  22  ;  for  example,  the  atomic  volumes 
of  formiate  of  methyl,  -GgH^Og,  and  butyrate  of  ethyl,  -GgHgOg, 
differ  by  nearly  4  x  22.  Acetate  of  ethyl,  -G^HgOg,  and 
butyrate  of  methyl,  -G-gHioOg,  whose  formulas  differ  by  -GHg, 
differ  in  atomic  volume  by  nearly  22.  The  same  law  holds 
good  with  respect  to  liquids  containing  sulphur,  chlorine, 
iodine,  bromine,  and  nitrogen  (see  Tables  B,  C,  D).  Again : 
by  comparing  the  atomic  volumes  of  analogous  chlorine  and 
bromine  compounds,  it  is  found  that  the  substitution  of  1,  2, 
or  3  atoms  of  bromine  for  an  equivalent  quantity  of  chlorine, 
increases  the  atomic  volume  of  a  compound  by  once,  twice, 
or  three  times  5.  This  will  be  seen  by  comparing  the  atomic 
volumes  of  PBrg  and  PCI3;  Q^^fi^  and  'G2H5CI,  &c. 
(Table  C.) 

2.  Isomeric  liquids  belonging  to  the  same  chemical  type  have 
equal  atomic  volumes.  —  The   atomic  volume   of  acetic  acid, 

^2^^]0,  is  between  63-5  and  63-8;  that  of  formiate  of 
methyl, £^TT  jO,  is  63  4  ;  the  atomic  volume  of  butyric  acid^ 
^A^jO,  is  between  106-4  and  107*8  ;  that  of  acetate  of 
ethyl,  ^^^aOj^^  -^  ij^tween  107-4  and  107-8. 

3.  In  liquids  of  the  same  chemical  type,  the  replacement  of 
hydrogen  by  an  equivalent  quantity  of  oxygen  (that  is  to  say, 
of  1  pt.  of  hydrogen  by  8  pts.  of  oxygen)  makes  but  a  slight 
alteration  in  the  atomic  volume. — This  may  be  seen  by  com- 
paring the  atomic  volumes  of  alcohol,  ^^fi-,  and  acetic 
acid,  JG2H4O2 ;  of  ether,  G^HjoO,  acetate  of  ethyl,  ^G^HgOg, 
and  anhydrous  acetic  acid,  4^411^03 ;  of  cymol,  Gj^Hj^,  and 


ATOMIC    VOLUME    OF   LIQUIDS.  573 

cuminol,  C^qR^^Q.  The  alteration  caused  by  the  substitution 
of  O  for  Hg  is  always  an  increase. 

4.  In  liquids  of  the  same  chemical  type,  the  replacement  of 
2  at  H  by  I  at.  Q  (I  pt.  by  weight  of  hydrogen  by  6  parts 
of  carbon)  makes  no  alteration  in  the  atomic  volume, — Such, 
for  example,  is  the  case  with  benzoate  of  ethyl,  -GgHjoOg,  and 
valerate  of  ethyl,  ^^Hj^Og,  and  with  the  corresponding  ben- 
zoates  and  valerates  in  general;  also  with  bitter  almond  oil, 
C-^HgO,  and  valeraldehyde,  -G^HjoO. 

In  liquids  belonging  to  different  types,  the  same  relations 
are  not  found  to  hold  good.  Moreover,  the  types  within 
which  these  relations  are  observed,  are  precisely  those  of 
Gerhardt's  classification  (II.  528).  Further,  when  liquid 
compounds  are  represented  by  rational  formulas  founded  on 
these  types,  their  atomic  volumes  may  be  calculated  from 
certain  fundamental  values  of  the  atomic  volumes  of  the 
elements,  on  the  supposition  that  the  atomic  volume  of  a 
liquid  compound  is  equal  to  the  sum  of  the  atomic  volumes 
of  its  constituent  elements. 

Since  the  addition  of  •G-H2  to  a  compound  increases  the 

atomic  volume  by  22,  this  number  may  be  taken  to  represent 

the  atomic  volume  of  "GHg ;  moreover,  since  Q-  (or  Og)  may 

take  the  place  of  Hg  in  combination,  without  altering  the 

atomic  volume  of  the  compound,  it  follows  that  the  atomic 

volume  of  •€•  must  be  equal  to  that  of  Hg ;  and  therefore  the 

22 
atomic  volume  of  G=  —  =  11,  and  that  of  Hg  also  equal 

to  11,  or  that  of  H=5'5.  Further,  as  the  substitution  of  O 
for  Hg  produces  a  slight  increase  in  the  atomic  volume  of  a 
compound,  the  atomic  volume  of  O  must  be  rather  greater 
than  11 ;  and  it  is  found  that,  by  assuming  the  atomic  volume 
of  O,  when  it  takes  the  place  of  Hg  (that  is  to  say,  in  a 
radical,  as  when  acetyl,  -GgHgO,  is  formed  from  ethyl,  GgH^), 
to  be  equal  to  12-2,  results  are  obtained  agreeing  very  nearly 
with  those  of  abservation.     But  when  oxygen  occupies  the 


574  ATOMIC   VOLUME   OF   LIQUIDS. 

XT 

position  which  it  has  in  water,  ttO,    its   atomic   volume    is 

smaller.     The  specific  gravity  of  water  at  the  boiling  point 

is  0-9579 ;  hence  its  atomic  volume  at  that  temperature  is 

18 
—         — 18*8  ;  now  the  2  atoms  of  hydrogen  occupy  a  space 
u  *  yo 7 y 

equal  to  11;  hence  the  volume  of  the  oxygen  is  7*8.  The 
same  value  of  the  atomic  volume  substituted  for  Q  in  the 
formulae  of  the  several  compounds  belonging  to  the  water- 
type,  in  which  it  occupies  a  similar  place,  that  is  to  say, 
outside  the  radical,  gives  results  agreeing  nearly  with  obser- 
vation. That  a  given  quantity  of  a  substance  should  occupy 
different  spaces,  under  different  circumstances,  is  a  fact  easily 
explained,  when  it  is  remembered  that  the  particles  of  a  body 
cannot  be  supposed  to  be  in  absolute  contact,  but  are  sepa- 
rated by  certain  spaces,  which  increase  or  diminish  according 
to  the  temperature  of  the  body,  and  according  as  it  is  in  the 
solid,  liquid,  or  gaseous  state. 

From  these  values  of  the  atomic  volumes  of  the  elements 
carbon,  hydrogen,  and  oxygen ;  viz.  — 

Atomic  volume  of  ^G       .         .         .         .  =  11 

„  „       xl        .  .  ,  .  =  o'o 

„  „       O  (within  the  radical)  =  12*2 

,,  Si       ^  (without  the  radical)  =  7*8  ; 

the  calculated  values  of  the  atomic  volumes  of  liquids,  in 
the  fourth  column  of  Table  A,  are  deduced.  The  method 
of  calculation  may  be  understood  from  the  following  ex- 
amples : 

Benzol,  QJi^  =  Q^U, .  H. 
Atomic  volume  of -Gg      .         .         .         ,  =  66 

a  99         -Hg        •  •  •  •   =   oo 

,,  „       benzol  .         .         .  =  99 


ATOMIC   VOLUME   OF   LIQUIDS.  575 


Aldehyde,  ^,H,0  = 

:  e,H3©. 

,H. 

,ic  volume  of  -Gg 

,            , 

. 

= 

22 

3>                         i9             ^A            • 

•              • 

. 

= 

22 

„              „       O  (within 

the  radical) 

= 

12-2 

„       aldehyde      .         .         .  =  56*2 
Alcohol,  G^HgO  =  ^AjQ, 


Atomic  volume  of  Q^      .         .         .         .  =  22 

39                        39 

H,      .         .         .         .  =  33 

99                         99 

O  (without  the  radical)  =     7*8 

99                        99 

alcohol         .         .         .  =  62-8 

Acetic  acid,  Q^U^Q,  =  ^^^^^]Q. 

Atomic  volume  of  Q^      •         •         •         .  =  22 

99                         99 

H,      .         .         .         .  =  22 

99                        99 

O  (within  the  radical)  =12-2 

JJ                             39 

O  (without  the  radical)  =     7*8 

99                          39 

acetic  acid  .         .         .  =  64*0 

Anhydrous  acetic  acid,  ■G^HgOg  =  jC^TT^ri^^* 

Atomic  volume  of  G^      .         .         .         .  =     44 

J5                         >J 

Hg      .         .         .         .  =     33 

33                        J> 

Og  (within  the  radical)  =     24-4 

33                         33 

O  (without  the  radical)  =       7*8 

JJ                         39 

anhydrous  acetic  acid  .  =  109*2 

Oxalate  of  methyl,  G^HgO^  =  (q^\  ]^2' 

Atomic  volume  of  ^4      .         .         .         ,  =     44 

99                        33 

Hg       .           .           .           .  =     33 

«                           33 

O2  (within  the  radical)  =     24*4 

93                          93 

O2  (without  the  radical)  =     15-6 

99                         39 

oxalate  of  methyl          .  =  117*0 

576 


AT03IIC    VOLUME    OF    LIQUIDS. 


Liquids  containing  Sulphur. — Sulphur  enters  into  combina- 
tion in  various  ways ;  sometimes  taking  the  place  of  oxygen 
in  the  type  HH .  O  (as  in  mercaptan) ;  sometimes  taking  the 
place  of  carbon  within  a  radical  (as  in  anhydrous  sulphurous 
acid)  iSO .  O,  compared  with  anhydrous  carbonic  acid  €0 . 0; 
sometimes  replacing  oxygen  within  a  radical  (as  in  sulphide 
of  carbon),  CS .  -S,  compared  with  anhydrous  carbonic  acid. 
In  the  first  and  second  cases,  the  atomic  volume  of  sulphur- 
compounds  may  be  calculated  by  attributing  to  sulphur  (S= 
32),  the  atomic  volume  22*6,  those  of  the  other  elements  re- 
maining as  above ;  in  the  third  case,  the  atomic  volume  of 
sulphur  appears  to  be  greater;  viz.,  28-6. 


Examples. — Mercaptan,  -GgHgS  = 

Atomic  volume  of  -Gg      • 
«<       He 


€„H. 


]^. 


H 
.  =  22 
=  33 
,  =  22-6 


77-6 


„  „       mercaptan   . 

Sulphide  of  carbon,  -GSg  =  GS*S. 
Atomic  volume  of  -Q       .         .         .         .  =  11 
„  „        ^  (within  the  radical)  =  28*6 

„  „        S  (without  the  radical)  =  22-6 


sulphide  of  carbon 


=  62-2 


Table  B. 
Atomic  Volumes  of  Liquid  Sulphur-compounds, 


Substance. 

Formula. 

Atomic  Volume  at  the  Boiling  Point. 

Weight. 

Calculated. 

Observed. 

Mercaptan     . 
Amylic  mercaptan 
Sulphide  of  methyl 
Sulphide  of  ethyl   . 
Bisulphide  of  methyl      . 
Sulphurous  acid     . 
Sulphite  of  ethyl    . 
Bisulphide  of  carbon      . 

€8, 

62 
104 
62 
90 
94 
64 
138 
76 

77-6 
143-6 

77-6 
121-6 
100-2 

42-6 
149-4 

62-2 

76-0...   76-1  at    36°  C. 
140-1. ..140-5  „   120 

75-7     .      .     „     41 
1205... 121-5  „     91 
100-6. ..100-7  „  114 

43-9     .      .     „    -8 
148-8... 149-5  „   160 

62-2...  62-4  „     47 

ATOMIC   VOLUME   OF   LIQUIDS. 


577 


Chlorides,  Bromides,  and  Iodides. — In  liquid  compounds  of 
this  class,  the  atomic  volume  of  CI  is  supposed  to  be  22*8, 
that  of  Br  =  27*8,  and  that  of  I  =  37 '5,  those  of  the  other 
elements  remaining  as  above. 


Table  C. 
Atomic  Volumes  of  Liquid  Chlorides,  Bromides,  and  Iodides. 


Atomic  Volume  at  the  Boiling 

Point. 

Substance. 

Formula. 

Atomic  

Weight.  ^^ 

Iculatec 

1.                  ObserTed. 

Bichlorinated  ethylene   . 

OJi^Cla 

97 

78-6 

79-9     .       .     at 

37°  C. 

Chloride  of  carbon 

o,ci. 

166 

113-2 

115-4     .       .     „ 

123 

Chloride  of  ethylene 

G,H,C], 

99 

896 

85-8...   86-4  „ 

85 

,  monochlorinated 

GJifih 

133'5 

106-9 

105-4... 107-2  „ 

115 

,  bichlorinated     . 

G,H,C1, 

168 

124-2 

120-7. ..121-4  „ 

137 

G2HCI5 

ono.f; 

141*'i 

143         .      .     „ 
129-5.. .133-7  „ 

154 
123 

Chloride  of  butylene 

O.HgCfz 

127 

It  1  0 
133-6 

Monochlorinated  chloride 

of  methyl  . 

GH2CI2 

85 

676 

64-5    .      .      „ 

30-5 

Chloroform    . 

OHCI3 

119-5 

84-9 

84-8...  85-7  „ 

62 

Chloride  of  carbon 

CCI4 

154 

102-2 

104-3. ..107-0  „ 

78 

Chloride  of  ethyl   . 

©aHsCl 

64-5 

72-3 

71-2...   74-5  „ 

11 

,  monochlorinated 

G2H4CI2 

99 

89-6 

86-9...   89-9  „ 

64 

,  bichlorinated    . 

O2H3CI3 

133-5 

106-9 

105-6...  109-7  „ 

75 

Chloride  of  amyl   . 

O^H.jCl 

lOG-5 

138-3 

135-4.. .137-0  „ 

102 

Chloral 

GJICI3O 

147-5 

108-1 

108-4.. .108-9  „ 

96 

Chloride  of  acetyl  . 

C^H.OCl 

78-5 

73-5 

74-4...   75-2  „ 

55 

Chloride  of  benzoyl 

G,H,0Q1 

140-5 

139-5 

134-2. ..137-8  „ 

198 

Bromine 

Br, 

160 

55-6 

54    ...  57-4  „ 

63 

Bromide  of  methyl 

OH^Br 

95 

55-3 

58-2     .      .     „ 

13 

Bromide  of  ethyl    . 

G^H.Br 

109 

77-3 

78-4     .      .     „ 

41 

Bromide  of  amyl    . 

0,H„Br 

151 

143-3 

149-2     .      .     „ 

119 

Bromide  of  ethylene 

0,H,Br, 

188 

99-6 

97-5...  99-9  „ 

130 

Iodide  of  methyl    . 

GH3I 

142-1 

65-0 

65-4...   68-3  „ 

43 

Iodide  of  ethyl 

G,H,I 

156-1 

87-0 

85-9...   86-4  „ 

71 

Iodide  of  amyl 

€^5HuI 

198-1 

153-0 

152-5... 155-8  „ 

147 

Chloride  of  sulphur 

SCI 

6T-5 

45-7     .      .     „ 

140 

Chloride  of  phosphorus  . 

PCI3 

137-5 

93-9     .      .     „ 

78 

Bromide  of  i)hosi)horus  . 

PBr3 

271 

108-6     .      .     „ 

175 

Chloride  of  silicon 

SiCL 

127-8 

91-6     .      .     „ 

59 

Bromide  of  silicon 

SiBrg 

261-3 

108-2     .      .     „ 

153 

Chloride  of  arsenic 

AsClg 

181-5 

94-8     .      .     „ 

133 

Chloride  of  antimony     . 

SbCl3 

2355 

100-7     .      .     „ 

223 

Bromide  of  antimony     , 

SbBrg 

369 

116-8     .      .     „ 

275 

Chloride  of  tin 

SnCL 

129 

65-7     .       .     „ 

115 

Chloride  of  titanium 

TiCl, 

96 

63-0     .      .     „ 

136 

^7^  ATOMIC   VOLUME   OF  LIQUIDS. 

The  compounds  PCI3,  SiClg,  and  AsClg  have  nearly  equal 
atomic  volumes,  whence  it  may  be  inferred  that  phosphorus, 
silicon,  and  arsenic,  in  their  liquid  compounds,  have  equal 
atomic  volumes.  The  same  conclusion  may  be  drawn  regard- 
ing tin  and  titanium,  since  the  atomic  volumes  of  SnClg  and 
TiClg  are  equal. 

Nitrogen-compounds.  —  In  compounds  belonging  to  the 
ammonia  type,  the  atomic  volume  of  nitrogen  is  2*3.  This 
result  is  deduced  from  the  observed  atomic  volume  of  ani- 
line, ^gH^N,  which  is  106 '8.  Now  the  atomic  volume  of 
6  €  +  7  H  =  6  .  11  +  7  .  5-5  =  104*5,  which  number, 
deducted  from  106  8,  leaves  2*3  for  the  atomic  volume  of 
nitrogen. 

The  atomic  volume  of  cyanogen  deduced  from  the  observed 
at.  vol.  of  cyanide  of  phenyl,  ^N  .  ^^5,  or  -Q^HgN,  is  nearly 
28.    Thus— 

Atomic  volume  of  ^^HgN  =    121*6 

9>  99  "^6^5  ^^  93*5 


„  „  €N         =     28-1 

A  similar  calculation,  founded  on  the  observed  atomic  volume 
of  cyanide  of  methyl,  ^gHgN,  gives,  for  the  at.  vol.  of 
cyanogen,  the  number  26*8.  The  atomic  volume  of  liquid 
cyanogen  determined  directly  at  37°  or  39°  C.  above  its  boiling 
point,  is  between  28*9  and  30*0.  As  a  mean  of  these  values, 
the  atomic  volume  of  cyanogen  may  be  assumed  to  be  28  ; 
and  with  this  value  the  atomic  volumes  of  the  liquid  cyanides 
are  calculated.     Thus,  for 

Oil  of  mustard  (sulpho-cyanide  of  allyl),€4H5NS  =  ^^  JS. 

Atomic  volume  of  C3H5         .         .         .  =     60*5 
„  „       GN  .         .         .=     28-0 

„  „      S  (without  the  radical)  =     22*6 


oil  of  mustard    .         .  =  111*1 


ATOMIC   VOLUME   OF   LIQUIDS. 


579 


The  atomic  volumes  of  compounds  containing  the  radical 
NO2  are  calculated  on  the  hypothesis  that  the  at.  vol.  of  that 
radical  is  33,  which  agrees  nearly  with  the  observed  atomic 
volume  of  liquid  peroxide  of  nitrogen.  Thus  : — the  at.  vol.  of 
nitrite  of  amyl,  ^gHj^NOg  =  at.  vol.  of  Q^B^^i  +  at.  vol. 
of  NO2  =  115-5    +   33   =    148-5. 

Table  D. 

Atomic  Volumes  of  Liquids  containing  Nitrogen. 


Atomic  Volume  at  the  Boiling  Point. 

Substance. 

Formula. 

Atomic 
Weight. 

Calculated. 

Observed. 

Ammonia 

H3N 

17 

18-8 

22-4...  23-3  at  10°. ..16°* 

Ethylamine   . 

G,H,N 

45 

62-8 

65-3     .        . 

at    18-7 

Butylamine    . 

0,H„N 

73 

106-8 

Amylamine   . 

G,H,3N 

87 

128-8 

125-0     .        . 

.     „     94 

Caprylamine 

GgHjgN 

129 

194*8 

190-0     .        . 

.     M  170 

Aniline 

G,H,N 

93 

106-8 

106-4.. .106-8 

.     „  184 

Toluidine 

aHoN 

107 

1288 

Ethaniline 

0,H„N 

121 

150-8 

1.50-6     . 

„  204 

Biethaniline  . 

0,oH,,N 

149 

194-8 

190-5     .       . 

.     „  213-5 

Cyanogen 

€N 

26 

28-0 

28-9...  300 

.     „     16 1 

Hydrocyanic  acid  . 

GHN 

27 

33-5 

391     .        . 

.     „     27 

Cyanide  of  methyl 

e,H3N 

41 

55-5 

54-3     .        . 

.     „     74 

Cyanide  of  ethyl    . 

^aH.N 

55 

77-5 

77-2     .       . 

„     88 

Cyanide  of  butyl    . 

G,H,N 

83 

121-5 

Cyanide  of  phenyl . 

e,H,N 

O2H3NS 

103 

121-5 

121-6. ..121-9 

„  191 

Sulphocyanide  of  methyl 

73 

78-1 

75-2...  78-2 

„   133 

Sulphocyanide  of  ethyl  . 

^gH^NS 

87 

100-1 

99-1     .       . 

,,    146 

Oil  of  mustard 

a.H^NS 

99 

111-1 

1131. ..114-2 

„   148 

Cyanate  of  ethyl    . 

OgHsNO 

71 

85-3 

84-3...  84-8 

„     60 

Peroxide  of  nitrogen 

NO3 

30 

33-0 

31-7...  32-4 

>,     40 1 

Nitrate  of  methyl  . 

GH3NO3 

77 

68-3 

69-4     .        . 

»     66 

Nitrate  of  ethyl 

O.H^NOg 

101 

90-3 

90-0...   90-1 

»     86 

Nitrobenzol 

GgH.NO, 

123 

126-5 

122-6.., 124-9 

„  218 

Nitrite  of  methyl   . 

eH3NO, 

61 

60-5 

61-6     . 

»      14§ 

Nitrite  of  ethyl 

G,H,NO, 

75 

82-5 

79-2...   84-6 

»     18 

Nitrite  of  amyl 

e,H„NO, 

117 

148-5 

148-4     .        . 

„     95 

*  Between  44°  and  50°  above  the  boiling  point, 
f  Between  37°  and  39°  above  the  boiling  point. 
%  About  35°  above  the  boiling  point. 
§  27°  above  the  boiling  point. 


580  ATOMIC  VOLUME   OF   LIQUIDS. 

From  the  preceding  observations  and  calculations,  it 
appears  that  the  atomic  volume  of  a  compound  depends,  not 
merely  on  its  empirical,  but  likewise  on  its  rational  formula  ; 
in  other  words,  not  merely  on  the  number  of  atoms  of  its 
elements,  but  further  on  the  manner  in  which  those  atoms 
are  arranged.  Now  it  has  been  shown  (p.  522)  that  a  com- 
pound may  have  more  than  one  rational  formula,  according  to 
the  manner  in  which  it  decomposes ;  and  hence  it  might 
appear  that  the  calculation  of  atomic  volumes  must  be 
attended  with  considerable  uncertainty,  inasmuch  as  the 
atomic  volumes  of  certain  elements,  as  oxygen  and  sulphur, 
vary  according  to  the  manner  in  which  they  enter  into  the 
compound.      Aldehyde,   for   example,    may   be   represented 

cither  as     ^tt^J^^  or  ^s      ^^     [;  and,  as  the  atomic  volume 

of  oxygen  is  12*2  or  7*8,  according  as  it  is  within  or  with- 
out the  radical,  the  atomic  volume  of  aldehyde  will  be 
56*2  if  deduced  from  the  type  HH,  and  51 '8  if  deduced 
from  the  type  HH .  O.  But  the  atomic  weight  of  aldehyde, 
and  its  specific  gravity  at  a  given  temperature  are  invariable ; 
it  cannot,  therefore,  have  two  different  atomic  volumes.  It 
must  be  remembered,  however,  that,  in  speaking  of  a  compound 
as  bavins  several  rational  formulae,  we  consider  it  rather  in  a 
dynamical  than  in  a  statical  point  of  view;  as  under  the 
influence  of  disturbing  forces,  and  on  the  point  of  undergoing 
chemical  change.  But  if,  on  the  other  hand,  we  regard  a 
compound  in  its  fixed  statical  condition,  as  a  body  possessing 
definite  physical  properties,  a  certain  specific  gravity,  a  cer- 
tain boiling  point,  rate  of  expansion,  refractive  power,  &c., 
we  can  scarcely  avoid  attributing  to  it  a  fixed  molecular 
arrangement,  or,  at  all  events,  supposing  that  the  disposition 
of  its  atoms  is  confined  within  those  limits  which  constitute 
chemical  types.  It  is  found,  indeed,  that  isomeric  liquids 
exhibit  equal  atomic  volumes  only  when  they  belong  to  the 
same  chemical  type.      If  this  view  be  correct,  the  relation 


ATOMIC   VOLUME    OF   LIQUIDS. 


581 


between  the  atomic  volumes  of  elements  and  compounds,  may 
often  render  valuable  service  in  determining  the  rational 
formula  which  belongs  to  a  compound  in  the  state  of  rest. 
Thus,  of  the  two  atomic  volumes  just  calculated  for  aldehyde, 
the  number  56*2,  deduced  from  the  formula  Q^H^Q  .  H, 
agrees  with  the  observed  atomic  volume  of  aldehyde,  which  is 
between  56*0  and  56*9,  better  than  51*8,  the  number  deduced 


from  ^2^3^^^ 


This  result  leads  to  the  conclusion  that  the 


aldehydes  belong  to  the  hydrogen-type  (p.  565),  rather  than  to 
the  water- type. 

There  are  many  groups  of  liquid  compounds,  irrespective 
of  isomerism  or  similarity  of  type,  the  members  of  which 
have  equal  or  nearly  equal  atomic  volumes.  The  following 
table  exhibits  the  calculated  atomic  volumes  of  several  of 
these  groups :  — 


Atomic  Volume  of  Liquids. 

Water 

H^O 

18-8 

Ether 

0,H,oO 

106-8 

Ammonia 

NH3 

18-8 

Butylic  alcohol 

«^ 

106-8 

Phenylic  alcohol 

0,H,0 

106-8 

Bromine  . 

Br, 

55-6 

Butylamine 

0,H.,N 

1068 

Cyanogen 

(ON), 

56-0 

Aniline    . 

4H7N 

106-8 

Aldehyde 

O2H4O 

56-2 

Butyric  acid     . 

O4H8O, 

108  0 

Cyanide  of  methyl    . 

O^HgN 

55-5 

Acetate  of  ethyl 

0,H,O, 

108-0 

Bromide  of  methyl   . 

O^HaBr 

55-3 

Anhydrous  acetic  acid 

0,H,03 

109-2 

Chloral     . 

O2HCIO 

108-1 

Alcohol    . 

0,HeO 

62-8 

Bichlorinated     chlo- 

Acetic acid 

0,H,0, 

64-0 

ride  of  ethyl 

0,H3Cl3 

106-9 

Formiate  of  methyl  . 

0,H,0, 

64-0 

Monochlorinated  chlo- 

Cyanate of  methyl    . 

0,H3NO, 

63-3 

ride  of  ethylene     . 

02H3C13 

1069 

Ethylamine 

O.H.N 

62-8 

Bromide     of     phos- 

Sulphide of  carbon   . 

0^; 

62-3 

phorus  . 

PBr3 

108-6 

Iodide  of  methyl 

0H3I 

65-0 

Valeraldehyde . 

0,H.,0 

122-2 

Acetone  . 

OaHeO 

78-2 

Cyanide  of  butyl 

0,H,N 

121-5 

Cyanide  of  ethyl 

e3H,N 

77-6 

Bitter  almond  oil 

0,H,O 

122-2 

Sulphocyanide  ofme- 

Cyanide  of  phenyl    . 

O^H.N 

121-5 

thyl      . 

O^HgNS 

78-1 

Sulphide  of  ethyl      . 

0,H,„S 

121-6 

Sulphide  of  methyl  . 

e.H,S 

77-6 

These  groups  exhibit  an  approach   to  the  uniformity  of 
atomic  volume  which  is  observed  in  the  gaseous  state. 

Berthelot  has  adduced  a  number  of  examples,  showing  that 

VOL.  II.  S  S 


582  ATOMIC   VOLUME   OF    SOLIDS. 

when  a  liquid  compound  is  formed  by  the  union  of  two  other 
liquids,  whose  specific  volumes  are  denoted  by  A  and  B, 
with  elimination  of  x  atoms  of  water,  the  specific  volume  of 
the  compound  is  nearly  =  A  -f-  B— .-cC  (the  atomic  volume  of 
water  being  denoted  by  C).  Berthelot's  observations,  how- 
ever, were  made  at  medium  temperatures,  not  at  the  boiling 
points  of  the  liquids. 

Atomk,  Volume  of  Solids, — The  principal  results  obtained  by 
Kopp,  with  reference  to  the  atomic  volume  of  solid  bodies, 
are  given  in  Yol.  I.  pp.  210 — 216.*  The  difficulty  of  reducing 
the  results  to  general  laws  is  similar  to  that  which  has  been 
noticed  in  the  case  of  liquids,  but  exists  to  a  still  greater 
extent,  inasmuch  as  our  knowledge  of  the  expansion  of  solids 
by  heat  is  much  more  limited  than  that  of  liquids.  It  is 
probable  that  the  atomic  volumes  of  solids  should  be  com- 
pared at  their  melting  points ;  since  it  is  only  at  those  tem- 
peratures that  the  effects  of  heat  upon  different  solids  can  be 
said  to  be  equal.  Now  the  specific  gravities  of  most  solids 
are  determined  only  at  medium  temperatures,  from  which 
the  melting  points  of  different  solids  are  separated  by  intervals 
of  very  different  magnitude ;  moreover,  there  are  but  few 
solids  whose  rate  of  expansion  at  different  temperatures  has 
been  ascertained  with  sufficient  accuracy  to  render  it  possible 
to  calculate  the  specific  gravities  at  the  melting  points.  A 
further  complication  arises  from  the  different  densities  which 
the  same  solid  often  exhibits,  according  as  it  is  amorphous  or 
crystalline,  or  according  to  the  particular  form  in  which  it 
crystallises. 

*  The  numbers  there  given  refer  to  the  oxygen-scale  of  atomic  weights. 
(0  =  100.) 


RELATIONS  OF  COMPOSITION  AND  BOILING  POINT.       583 


RELATIONS    BETWEEN  CHEMICAL  COMPOSI- 
TION AND   BOILING   POINT.* 

In  compounds  of  similar  constitution,  and  especially  among 
the  members  of  homologous  series  (p.  532),  difference  of  boiling 
point  is  frequently  proportional  to  difference  of  composition. 

1.  In  the  alcohols,  ^0^20+2^*  the  fatty  acids,  ^uHgnOg,  and 
the  compound  ethers  (p.  545)  isomeric  with  the  fatty  acids,  a 
difference  of  ^Hg  in  the  formula  corresponds  to  a  difference 
of  19°  C.  in  the  boiling  point. 

2.  The  boiling  point  of  a  fatty  acid,  ^..HanOg,  is  higher  by 
40°  C.  than  that  of  the  corresponding  alcohol,  ^nIl2n+2^» 

3.  The  boiling  point  of  a  compound  ether,  ^nH2n02,  is 
lower  by  82°  C.  than  that  of  the  isomeric  acid. 

Starting  from  the  observed  boiling  point  of  common 
alcohol,  78°  C,  and  calculating  by  these  rules  the  boiling 
points  of  the  other  alcohols  and  of  the  fatty  acids  and  ethers, 
we  obtain  the  numbers  in  the  third  column  of  the  following 
table,  which  do  not  differ  from  the  observed  boiling  points  in 
the  fourth  column,  more  than  these  latter,  as  determined  by 
different  observers,  differ  from  one  another. 


Substance. 


Alcohols. 

Methylic  alcohol 

Propylic  alcohol 
Butylic  alcohol 

Amy  lie  alcohol 

Cetylic  alcohol 


Formula. 


Boiling  point. 


Calculated. 


59° 

97 
116 

135 

344 


Observed. 


60° 

61 

64-9 

65 

96 
109 
1  ?0-4 
132 
132 
360 


at  744  mm. 
,,  755 
„  754 
„  752 
„  ? 
„  ? 
„  742 
„  760 
,,  766 


Observers. 


Kane. 
DelfFs. 
H.  Kopp. 
H.  Kopp. 
Chancel. 
Wurtz. 
H.  Kopp. 
Cahours. 
DelfFs. 
Favre  and 
Silbermann. 


*  H.  Kopp.  Ann.  Ch.  Pharm.  xcvi.  2,  330. 
S  s  2 


584      RELATIONS  OP  COMPOSITION  AND  BOILING  POINT. 


Boiling  point. 

Substance. 

Formula. 

Observed. 

Calculate 

i.                     Observed. 

Acids. 

Formic  acid   . 

€HA 

99 

r       98-5    . 
105-4    . 

.    at  753 
.     „  764 

mm. 

It 

Liebig. 
H.  Kopp. 

Acetic  acid    . 

0,H,0, 

118    • 

"     116-9    . 
116       . 

.     „  750 
.     „  754 

»» 

H.  Kopp. 
Delffs. 

Propionic  acid 

03HeO, 

137 

^     141-6    . 
L     141       . 

.     „  754-6  „ 

H.  Kopp. 
Limpricht 

and  V.  Uslar. 

Butyric  acid  . 

0,H«0, 

156 

r     156       . 
L     163       . 

.     „  733 
.     „  751 

>» 

H.  Kopp. 
L  Pierre. 

Valerianic  acid 

^5H.o^2 

175 

174-5    . 
L     175-8    . 

.     „  762     „ 
.     „  746-5  „ 

Delffs. 
H.  Kopp. 

Caproic  acid  . 

^6  "12^2 

194 

198       . 

.     „     ? 

» 

Brazier    and 
Gossleth. 

Caprylic  acid . 

O^H.eO, 

232 

236       . 

.     „     ? 

»» 

Fehling. 

Pelargonic  acid 

Q,R,,^, 

251 

260       . 

.     »     ? 

» 

Cahours. 

Compound  Ethers. 

Formiate  of  methyl. 

0,HA 

36    ■ 

r      32-7    . 
L       22-9    . 

.     «  741 

.     „  752 

» 

H.  Kopp. 
Andrews. 

'■       55       . 

.     „  762 

ti 

Andrews. 

Acetate  of  methyl  . 

GgHgO, 

55    • 

55-7    . 

.     „  757 

it 

H.  Kopp. 

59-5    . 

.     „  761 

»> 

L  Pierre. 

'       52-9    . 

.     „  752 

>» 

L  Pierre. 

Formiate  of  ethyl   . 

^sHe^a 

55 

53       . 

.     „  736 

)> 

Delffs. 

54-7    . 

.     ,,  754 

»» 

H.  Kopp. 

Acetate  of  ethyl      . 

e,H30, 

74    ■ 

'       73-7    . 
L       74-1    . 

.     »  745 
.     „  766 

»» 

H.  Kopp. 
I.  Pierre. 

93       . 

.     „  744 

» 

Delffs. 

Butyrate  of  methyl. 

e^H.oO, 

93 

95-1    . 
102-1    . 

.     „  742 
.     »  744 

>» 

H.  Kopp. 
L  Pierre. 

Acetate  of  propyl   . 

e^H.oO., 

93 

90  (abou 

t) 

Berthelot. 

Propionate  of  ethyl. 

G,H,oO, 

93 

95-8...   9 

8 

>» 

H.  Kopp. 

Valerate  of  methyl . 

G,H.,0, 

112 

114    ...11 

5     „  756 

»» 

H.  Kopp. 

Butyrate  of  ethyl    . 

GeH,,0, 

112 

f     114-6    . 
119       . 

.     „  756 
.     »  747 

» 

H.  Kopp. 
I.  Pierre. 

Formiate  of  amyl   . 

^6H,20, 

112 

'■     114       . 
116  (abou 

.     „  771 
t) 

»» 

Delffs. 
H.  Kopp. 

Acetate  of  butyl     , 

€,H,,0, 

112 

114 

Wurtz. 

Valerate  of  ethyl    . 

G,H.,0, 

131 

'     131-3    . 
133-2    . 

.     „  735 

.     „  754 

Delffs. 
H.  Kopp. 

133       . 

.     „  760 

" 

Delffs. 

Acetate  of  amyl 

^vH.A 

131 

133-3    . 

.     M  749 

H.  Kopp. 

137-6    . 

.     „  746 

11 

H.  Kopp. 

Valerate  of  amyl    . 

e.oH,oO» 

188 

187-8. ..18 

8-3  „  730 

>» 

H.  Kopp. 

It  appears  from  this  table  that  isomeric  compound  ethers 
have  equal  boiHng  points,  e.g,  formiate  of  ethyl  and  acetate  of 


RELATIONS  OF  COMPOSITION  AND  BOILING  POINT.      585 

methyl  boil  at  66° ;  valerate  of  methyl,  butyrate  of  ethyl,  for- 
miate  of  amy  I,  and  acetate  of  butyl,  boil  at  1 1 2°.  It  follows, 
also,  from  the  preceding  laws,  that  the  boiling  point  of  an 
acid,  QJl2x/^2i  ^^  ^^°  higher  than  that  of  its  methylic  ether, 
44°  higher  than  that  of  its  ethylic  ether,  and  13°  lower  than 
that  of  its  amylic  ether:  thus,  valerianic  acid  boils  at  175°; 
valerate  of  methyl  at  112° ;  valerate  of  ethyl  at  131° ;  valerate 
of  amyl  at  188°.     Common  ether,  ("^2^5)2^^  ^^  ^^®  ethyl-salt 

p    XT 

of  alcohol,    A  ^]0,  regarded  as  an  acid;   that  is  to  say,  it 

bears  the  same  relation  to  alcohol  that  acetate  of  ethyl  bears 
to  acetic  acid :  hence  its  boiling  point  should  be  78°  — 44°  =  34°. 
The  actual  observations  of  the  boiling  point  of  ether  vary 
from  34°  to  35-7°. 

In  the  same  series  of  homologous  compounds,  it  is  found 
that  the  addition  of  w  -G  raises  the  boiling  point  by  w .  29°  ;  and 
the  addition  of  ^^  H  lowers  the  boiling  point  by  n  .  5°  [conse- 
quently, the  addition  of  nGHg  raises  it  by  w.  (29  — 2x5) 
=  n,  19°].  The  same  law  is  likewise  observed  in  other  series 
of  compounds  of  similar  character.  Thus,  benzoate  of 
ethyl,  GgHjoOg,  boils  at  209°,  which  is  higher  by  4  x  29, 
or  116,  than  the  boiling  point  of  the  ethers  G^Hj^Og, — 
butyrate  of  methyl  for  example.  The  boiling  point  of  angelic 
acid,  GgHgOg,  is  higher  by  29°  than  that  of  butyric  acid, 
C^HgOg ;  and  2  x  5,  or  10°,  higher  than  that  of  valerianic 
acid,  -GgHjoOg.  The  boiling  point  of  phenylic  alcohol,  GgHgO, 
is  higher  by  about  4  x  29,  or  116°,  than  that  of  common 
alcohol,  Grfi.fi- ;  and  about  8  x  5,  or  40°,  higher  than  that  of 
caproic  alcohol,  GgH^^O. 

Constant  relations  of  composition  and  boiling  point  are 
observed  also  in  other  series  of  homologous  compounds ;  but 
the  difference  of  boiling  point  corresponding  with  a  difference 
of  GH2,  is  not  always  19°.  In  the  series  of  hydrocarbons  : — 
benzol, -GsHe  (B.P.^80°),  toluol,  G^Hg,  xylol,  GgH^o,  cumol, 
G9H12,  cymol,  ^iqHj^,  the  difference  is  24°;  in  the  homologous 

s  s  3 


586  CHEMICAL    AFFINITY. 

compounds:  —  bromide  of  ethylene,  4^2H4Br2,  bromide  of  pro- 
pylene, Q^HqEv^,  bromide  of  butylene,  QJIfir^,  it  is  15°, 
their  boiling  points  being  130°,  145°,  and  160°,  respectively. 
In  the  series  of  alcohol-radicals  (in  the  free  state),  the  difference 
is  about  23° ;  in  the  anhydrous  acids,  homologous  with  an- 
hydrous acetic  acid,  it  is  about  13°. 

These  differences  of  boiling  point  would  probably  be  the 
same  in  all  series  of  homologous  compounds,  if  the  boiling 
points  were  determined  at  different  pressures.  It  is  not, 
indeed,  to  be  expected  that  two  substances  should  exhibit  the 
same  difference  of  boiling  point  under  all  pressures ;  for  if 
B  and  B'  denote  the  boiling  points  of  two  liquids  at  the 
ordinary  atmospheric  pressure,  b  and  b',  the  boiling  points  of 
the  same  liquids  at  another  pressure ;  and  if  we  suppose  that 

B  _  B'    =    b  -  b', 

it  will  follow  that 

B  -  b  =  B'-V; 

that  is  to  say,  the  boiling  points  of  the  two  liquids  would  vary 
equally  for  equal  differences  of  pressure,  which  is  contrary  to 
observation. 


CHEMICAL    AFFINITY. 

Tnjfluenoe  of  mass  on  chemical  action.  —  That  the  relative 
degrees  of  affinity  of  a  body  for  a  number  of  others  to  which 
it  is  simultaneously  presented,  are  greatly  modified  by  their 
relative  masses,  was  first  pointed  out  by  Berthollet  The  law 
laid  down  by  that  philosopher  respecting  the  action  of  masses, 
is  this : — A  body  to  which  two  different  substances,  capable  of 
uniting  with  it  chemically ,  are  presented  in  different  proportions, 
divides  itself  between  them  in  the  ratio  of  the  products  of  their 
7nasses,  and  the  absolute  strenaths  of  their  affnities  for  the  first 


CHEMICAL   AFFINITY.  587 

hodij.  Thus,  if  we  denote  by  A  and  B  the  masses  of  the  two 
bodies  which  are  present  in  excess,  by  a  and  /3,  the  coefficients 
of  their  absohite  affinities  for  the  body  C ;  and  by  a  and  6, 
the  quantities  of  A  and  B,  which  actually  combine  with  C, 
the  law  just  stated  will  be  expressed  by  the  proportion: — 

a     :     h    :=    uA     :     ^B, 

If  this  view  be  correct,  any  alteration,  however  small,  in  the 
relative  quantities  of  A  and  B,  must  produce  a  corresponding 
alteration  in  the  relative  quantities  of  the  two  which  unite 
with  C,  That  this  is  not  the  case  under  all  circumstances,  is 
shown  by  the  following  experiments  of  Bunsen  and  of  Debus. 

Bunsen's  experiments,*  which  were  made  in  such  a  manner 
that  all  the  phenomena  of  combination  concerned  in  them  took 
place  simultaneously,  lead  to  the  following  remarkable  laws : — • 

1.  When  two  or  more  bodies,  B  B' ,  .  ,  are  presented  in 
excess  to  the  body  JL,  under  circumstances  favourable  to  their 
combination  with  it,  the  body  A  always  selects  of  the  bodies 
B  B'  ,  ,  ,  quantities  which  stand  to  one  another  in  a  simple 
atomic  relation,  so  that  for  1,  2,  3  .  .  .  atoms  of  the  one  com- 
pound, there  are  always  formed  1,  2,  3  .  .  .  atoms  of  the  other ; 
and  if  in  this  manner  there  is  formed  an  atom  of  the  compound 
AB',  in  conjunction  with  an  atom  of  AB,  the  mass  of  the  body 
B  may  be  increased  relatively  to  that  of  B^,  up  to  a  certain 
limit,  without  producing  any  alteration  in  the  atomic  pro- 
portion. 

When  carbonic  oxide  and  hydrogen  are  exploded  with  a 
quantity  of  oxygen  not  sufficient  to  burn  them  completely,  the 
oxygen  divides  itself  between  the  two  gases  in  such  a  manner 
that  the  quantities  of  carbonic  acid  and  water  produced  stand 
to  one  another  in  a  simple  atomic  proportion.  The  results  of 
Bunsen's  experiments  are  given  in  the  following  table,  the 
numbers  in  which  denote  volumes :  — 

♦  Ann  CIi.  Fliann.  Ixxxv.  j37. 

s  s  4 


588 


CHEMICAL   AFFINITY. 


Composition  of  Gaseous  Mixture. 

Quantities  of  CO  and  H  con- 
sumed by  Detonation. 

Ratio  of 

CO:  H. 

72-57  CO     .     18-29  H     .       9*14  0 
59-93    „       .     26-71  „      .     13-36  „ 
36-70    „       .     42-17  „      .     21-13  „ 
40-12    „       .     47-15  „      .     12-73  „ 

12-18  CO     .        6-10  H 

13-06    „       .      13-66  „ 

10-79    „       .     31-47  „ 

4-97    „       .     20-49  „ 

2  :  1 
1  :  1 
1  :3 
1  :  4 

The  results  were  the  same  whether  the  explosion  took  place 
in  the  dark,  in  diffused  daylight,  or  in  sunshine ;  and  were 
not  affected  by  the  pressure  to  which  the  gaseous  mixture  was 
subjected. 

The  proportions  of  hydrogen  and  carbonic  acid  consumed 
in  these  several  experiments,  correspond  with  the  composition 
of  five  hydrates  of  carbonic  acid,  containing,  respectively — 


HO.2CO2;  HO. CO, 


2H0.C0 


2 ' 


3HO.CO2;  4H0.C0, 


but  the  results  cannot  be  attributed  to  the  actual  formation  of 
these  hydrates,  inasmuch  as  hydrates  of  acids  containing 
several  atoms  of  water  are  incapable  of  existing  at  high 
temperatures. 

2.  When  a  body.  A,  exerts  a  reducing  action  on  a  com- 
pound, BC,  present  in  excess,  so  that  A  and  JB  combine 
together,  and  C  is  set  free ;  then,  if  C  can,  in  its  turn,  exert  a 
reducing  action  on  the  newly-formed  compound,  AB,  the  final 
result  of  the  action  is,  that  the  reduced  portion  of  BC  is  to 
the  unreduced  portion  in  a  simple  atomic  proportion. 

In  this  case,  also,  the  mass  of  the  one  constituent  may, 
without  altering  the  existing  atomic  relation,  be  increased  to  a 
certain  limit,  above  which  that  relation  undergoes  changes 
by  definite  steps,  but  always  in  the  proportion  of  simple 
rational  numbers. 

When  vapour  of  water  is  passed  over  red-hot  charcoal,  the 
carbon  is  oxidised  and  hydrogen  is  separated ;  but  the  process 
does  not  go  on  so  far  as  the  complete  formation  of  carbonic 
acid,  but  stops  at  the  point  at  which  1  vol.  carbonic  acid 
and  2  vol.  carbonic  oxide  are  formed  to  every  4  vol.  of 
hydrogen. 


CHEMICAL   AFFINITY.  589 

In  the  imperfect  combustion  of  cyanogen — the  gaseous 
mixture  being  so  far  diluted  that  it  will  but  just  explode,  in 
order  that  the  temperature  may  not  rise  too  high,  and  the 
result  be  consequently  vitiated  by  the  partial  oxidation  of  the 
nitrogen — carbonic  acid  and  carbonic  oxide  are  formed,  and 
nitrogen  set  free,  likewise  in  simple  atomic  proportion.  A 
mixture  of  18*05  vol.  cyanogen,  28*87  oxygen,  and  53*08 
nitrogen,  gave,  by  detonation,  2  vol.  carbonic  oxide,  and  4  vol. 
carbonic  acid  to  3  vol.  nitrogen. 

In  the  combustion  of  a  mixture  of  carbonic  acid,  hydrogen, 
and  oxygen,  in  which  the  carbonic  acid  is  exposed  at  the  same 
time  to  the  reducing  action  of  the  hydrogen  and  the  oxidising 
action  of  the  oxygen,  the  reduced  portion  of  the  carbonic  acid 
is  likewise  found  to  bear  to  the  unreduced  portion  a  simple 
atomic  relation.  In  the  combustion  of  a  mixture  of  8*52 
carbonic  acid,  70*33  hydrogen,  and  21*15  oxygen,  the  result- 
ing carbonic  oxide  was  to  the  reduced  carbonic  acid  in  the 
ratio  of  3  .*  2.  After  the  combustion  of  a  mixture  of  4*41  vol. 
carbonic  oxide,  2*96  carbonic  acid,  68*37  hydrogen,  and 
24*  Z.  6  oxygen,  the  volume  of  the  carbonic  oxide  converted 
into  carbonic  acid  by  oxidation,  was  to  that  of  the  residual 
carbonic  oxide  as  1:3. 

That  these  remarkable  laws  had  not  been  previously 
observed  is  attributed  by  Bunsen  to  the  fact  that  they  held 
good  only  when  the  phenomena  of  combination,  which  are 
regulated  by  them,  take  place  simultaneously ;  for,  even  if  a 
body  A,  were  originally  to  select  for  combination  from  the 
bodies  B  and  (7,  quantities  bearing  to  one  another  a  simple 
atomic  relation,  but  the  combination  of  A  and  B  were  to 
take  place  in  a  shorter  time  than  that  of  A  and  C,  it  would 
follow  of  necessity,  that  during  the  whole  of  the  process,  the 
ratio  of  B  to  C,  and  therefore,  also  the  atomic  relations  of  the 
associated  compounds,  would  change,  so  that  the  observed 
proportion  would  be  no  longer  definite.  The  same  result 
must  follow  if  the  bodies  which  are  combining  side  by  side 
are  not  homogeneously  mixed  in  the  beginning. 


590  CHEMICAL   AFFINITY. 

With  regard  to  the  bearing  of  these  results  on  Berthollet's 
law,  it  might  be  objected  that,  in  some  of  the  experiments,  as 
in  the  combustion  of  a  mixture  of  carbonic  oxide,  hydrogen, 
and  oxygen,  one  of  the  products,  viz.  the  water,  is  removed  from 
the  sphere  of  action  by  condensation,  and  that  the  circum- 
stances are  therefore  similar  to  the  removal  of  an  insoluble 
product  by  precipitation  (I.  231).  It  is  scarcely  conceivable, 
however,  that  a  reverse  action  would  take  place,  even  if  tlie 
gaseous  mixture  were  to  remain  at  the  temperature  which  exists 
during  the  combustion.  Moreover,  in  the  decomposition  of 
vapour  of  water  by  red-hot  charcoal,  the  whole  of  the  pro- 
ducts remain  in  the  gaseous  state. 

Debus*  has  obtained  results  similar  to  those  of  Bunsen  by 
precipitating  mixtures  of  lime  and  baryta-water  with  aqueous 
carbonic  acid,  or  mixtures  of  cliloride  of  barium  and  chloride 
of  calcium,  with  carbonate  of  soda.  A  small  quantity  of  a 
very  dilute  solution  of  carbonate  of  soda,  added  to  a  liquid 
containing  5  pts.  of  chloride  of  barium  to  1  pt.  of  chloride 
of  calcium,  threw  down  nearly  pure  carbonate  of  lime; 
but  when  the  proportion  of  the  chloride  of  barium  in  the 
mixture  was  5*7  times  as  great  as  that  of  the  chloride  of  cal- 
cium, 2*3  pts.  of  the  former  were  decomposed  to  1  pt.  of  the 
latter.  Hence  it  appears  that,  in  this  reaction  also,  limits  exist 
at  which  the  ratio  of  the  affinities  undergoes  a  sudden  change. 
In  these  experiments,  however,  the  products  are  imme- 
diately removed  from  tlie  sphere  of  action,  and  the  results  are 
therefore  not  comparable  with  those  which  are  obtained  when 
all  the  substances  present  remain  mixed  and  free  to  act  upon 
each  other. 

The  latter  condition  is  most  completely  fulfilled  in  the 
mutual  actions  of  liquid  compounds,  such  as  solutions  of 
salts,  when  all  the  possible  products  of  their  mutual  actions 
are  likewise  soluble ;  as,  for  example,  when  nitrate  of  soda  in 
solution  is  mixed  with  sulphate  of  copper.  Tlie  question  to 
be  solved  in  such  cases  is  this.  Suppose  two  salts  AB,  CD, 
*  Ann.  Ch.  Pliarm.  Ixxxv.  103.  ;  Ixxxvi.  156.  j  Ixxxvii.  238. 


CHEMICAL   AFFINITY.  591 

the  elements  of  which  can  form  only  soluble  products  by  their 
mutual  interchange,  to  be  mixed  together  in  solution.  Will 
these  elements,  according  to  their  relative  affinities,  either 
remain  in  their  original  state  of  combination,  as  AB  and  CD, 
or  pass  completely  into  the  new  arrangement  AD  and  CB  ? — or 
will  each  of  the  two  acids  divide  itself  between  each  of  the  two 
bases,  producing  the  four  compounds  AB,  AD,  BC,  BD  ?  — 
and,  if  so,  in  what  manner  will  the  relative  quantities  of  these 
four  compounds  be  affected  by  the  original  quantities  of  the 
two  salts  ?  Do  the  amounts  of  AD  and  CB,  produced  by  the 
reaction,  increase  progressively  with  the  regular  increase  of 
AB,  as  required  by  Berthollet's  theory?  or  do  sudden  tran- 
sitions occur,  like  those  observed  in  the  experiments  of  Bunsen 
and  Debus  ? 

The  solution  of  this  question  is  attended  with  considerable 
difficulty.  For  when  two  salts  in  solution  are  mixed,  and 
nothing  separates  out,  it  is  by  no  means  easy  to  ascertain  what 
changes  may  have  taken  place  in  the  liquid.  The  ordinary 
methods  of  ascertaining  the  composition  of  the  mixture,  such 
as  concentration,  or  precipitation  by  re-agents,  are  inadmis- 
sible, because  any  such  treatment  immediately  alters  the 
mutual  relation  of  the  substances  present.  In  some  cases, 
however,  the  mixture  of  two  salts  is  attended  with  a  decided 
change  of  colour,  without  any  separation  of  either  of  the  con- 
stituents, and  such  alterations  of  colour  may  afford  indications 
of  the  changes  which  take  place  in  the  arrangement  of  the 
molecules.  This  method  has  been  employed  by  Dr.  Glad- 
stone*, who  has  carefully  examined  the  changes  of  colour 
attending  the  mixture  of  a  great  variety  of  salts,  and  applied 
the  results  to  the  determination  of  the  effect  of  mass  in 
influencing  chemical  action. 

Dr.  Gladstone's  principal  experiments  were  made  with  the 
blood-red  sulphocyanide  of  iron,  which  is  formed  on  adding 
hydro-sulphocyanic  acid  or  any  soluble  sulphocyanide  to  a 
solution  of  a  ferric  salt  (I.  532).     On  mixing  known  quantities 

*  PhiL  Trans,  1855,  179 ;  Chem.  Soc.  Qu.  Jo.  ix.  54. 


592 


CHEMICAL   AFFINITY. 


of  different  ferric  salts  with  known  quantities  of  different 
sulphocyanides,  it  was  found  that  the  iron  was  never  com- 
pletely converted  into  the  red  salt;  that  the  amount  of  it  so 
converted  depended  on  the  nature  both  of  the  acid  combined 
with  the  ferric  oxide,  and  of  the  base  combined  with  the  sul- 
phocyanogen;  and  that  it  mattered  not  how  the  bases  and 
acids  had  been  combined  previous  to  their  mixture,  so  long  as 
the  same  quantities  were  brought  together  in  solution.  The 
effect  of  mass  was  tried  by  mixing  equivalent  proportions  of 
ferric  salts  and  sulphocyanides,  and  then  adding  known 
amounts  of  one  or  the  other  compound.  It  was  found  that, 
in  either  case,  the  amount  of  the  red  salt  was  increased,  and 
in  a  regular  progression  according  to  the  quantity  added. 
When  sulphocyanide  of  potassium  was  mixed  in  various  pro- 
portions with  ferric  nitrate,  chloride,  or  sulphate,  the  rate  of 
variation  appeared  to  be  the  same,  but  with  hydrosulpho- 
cyanic  acid  it  was  different.  The  deepest  colour  was  pro- 
duced when  ferric  nitrate  was  mixed  with  sulphocyanide  of 
potassium ;  but  even  on  mixing  1  eq.  of  the  former  with  3  eq. 
of  the  latter,  only  0*194  eq.  of  the  red  sulphocyanide  of  iron 
was  formed;  and  even  when  375  eq.  of  sulphocyanide  of 
potassium  had  been  added,  there  w^as  still  a  recognisable 
amount  of  ferric  nitrate  undecomposed.  The  results  of  a 
series  of  experiments  with  ferric  nitrate  and  sulphocyanide  of 
potassium  are  given  in  the  following  table :  — 


Ferric 

Sulphocyanide  of 

Red  Salt 

Ferric 

Sulpliocyanide  of 
Potassium. 

Red  Salt 

Nitrate. 

Potassium. 

produced. 

Nitrate. 

produced. 

1  equiv. 

3  equiv. 

88 

1  equiv. 

63  equiv. 

356 

6       „ 

127 

99      „ 

419 

1 

J 

96    „ 

156 

135      „ 

487 

12-6    „ 

176 

189      „ 

508 

16-2    „ 

195 

243      „ 

539 

1 

19-2    „ 

213 

1 

297      „ 

560 

28-2    „ 

266 

375      „ 

587 

46-2    „ 

318 

CHEMICAL   AFFINITT.  593 

The  addition  of  a  colourless  salt  reduced  the  colour  of  a 
solution  of  ferric  sulphocjanide,  the  reduction  increasing  in  a 
regularly  progressive  ratio,  according  to  the  mass  of  the 
colourless  salt. 

Similar  results  were  obtained  with  other  ferric  salts,  viz., 
with  the  black  gallate,  the  red  meconate  and  pyromeconate, 
the  blue  solution  of  Prussian  blue  in  oxalic  acid,  &c.,  and 
likewise  with  the  coloured  salts  of  other  metals,  e.  g,  the 
scarlet  bromide  of  gold,  the  red  iodide  of  platinum,  the  blue 
sulphate  of  copper,  when  treated  with  different  chlorides,  &c. 

The  amount  of  fluorescence  exhibited  by  a  solution  of  acid 
sulphate  of  quinine  w^as  found  to  be  affected  by  the  mixture 
of  a  chloride,  bromide,  or  iodide,  according  to  the  nature  and 
mass  of  the  salt  added ;  and  the  addition  of  sulphuric,  phos- 
phoric, nitric,  and  other  acids  was  found  to  produce  a  fluo- 
rescence in  solutions  of  hydrochlorate  of  quinine  or  of  sulphate 
which  had  been  rendered  non-fluorescent  by  the  addition  of 
hydrochloric  acid.  Solutions  of  horse-chestnut  bark,  and  of 
tincture  of  thorn-apple,  yielded  similar  results. 

The  conclusions  to  be  drawn  from  Dr.  Gladstone's  experi- 
ments, which  afford  a  complete  confirmation  of  BerthoUet's 
theory,  so  far  at  least  as  relates  to  the  action  of  substances  in 
solution,  are  as  follows  :  — 

When  two  or  more  binary  compounds  are  mixed  under 
such  circumstances  that  all  the  resulting  compounds  are  free 
to  act  and  react,  each  electro-positive  element  enters  into 
combination  with  each  electro-negative  element  in  certain 
constant  proportions,  which  are  independent  of  the  manner  in 
which  the  different  elements  are  primarily  arranged,  and  are 
not  merely  the  resultant  of  the  various  strengths  of  affinity  of 
the  several  substances  for  each  other,  but  are  dependent  also 
on  the  mass  of  each  of  the  substances  present  in  the  mixture. 
All  deductions  respecting  the  arrangement  of  substances  in  solu- 
tion, drawn  from  such  empirical  rules  as  that  the  strongest  acid 
combines  with  the  strongest  base,  must  therefore  be  fallacious. 


594  CHEMICAL   AFFINITY. 

An  alteration  in  the  mass  of  any  of  the  binary  compounds 
present  alters  the  amount  of  every  one  of  the  otlier  binary 
compounds,  and  that  in  a  regularly  progressive  ratio,  sudden 
transitions  only  occurring  where  a  substance  is  present  which 
is  capable  of  combining  with  another  in  more  than  one  pro- 
portion. 

This  equilibrium  of  affinities  arranges  itself  in  most  cases 
in  an  inappreciably  short  time ;  but,  in  certain  instances,  the 
elements  do  not  attain  their  final  state  of  combination  for  hours. 

Totally  different  phenomena  present  themselves  where  pre- 
cipitation, volatilisation,  crystallisation,  and  perhaps  other 
actions  occur,  simply  because  one  of  the  substances  is  thus 
removed  from  the  field  of  action,  and  the  equilibrium,  which 
was  at  first  established,  is  thus  destroyed  (I.  231). 

The  reciprocal  action  of  salts  in  solution  has  also  been 
examined  by  Malaguti*,  whose  method  consists  in  taking  two 
salts,  both  of  which  are  soluble  in  w*ater,  but  only  one  of 
which  is  soluble  in  alcohol,  mixing  them  in  equivalent  pro- 
portions in  water,  then  pouring  the  aqueous  solution  into  a 
large  quantity  of  alcohol,  and  analysing  the  precipitate,  in 
order  to  ascertain  the  quantities  of  the  original  salts  which 
have  been  decomposed.  Malaguti  concludes  from  his  experi- 
ments that,  in  the  mutual  action  of  two  salts,  if  nothing  se- 
parates from  the  liquid,  the  decomposition  is  most  complete 
when  the  strongest  acid  and  the  strongest  base  are  not  origi- 
nally united  in  the  same  salt,  and  that  two  experiments  of 
this  kind,  made  in  opposite  ways,  must  lead  to  the  same  final 
result ;  that,  for  example,  when  1  eq.  of  acetate  of  baryta  is 
added  to  1  eq.  of  nitrate  of  lead,  the  quantities  of  nitrate  of 
baryta  and  nitrate  of  lead  ultimately  present  in  the  liquid  are 
the  same  as  when  1  eq.  nitrate  of  baryta  is  mixed  with  1  eq. 
acetate  of  lead.  The  greater  the  quantity  of  the  two  salts 
decomposed  in  the  one  case,  the  smaller  will  be  the  quantity 

♦  Ann.  Ch.  Phys.  [3],  xxxvii.  198. 


CHEMICAL    AFFINITY. 


595 


decomposed  in  the  other :  so  that  if  the  quantity  of  any  salt, 
out  of  100  parts,  which  is  decomposed  by  the  action  of  another 
salt  (always  supposing  that  the  whole  remains  in  solution)  be 
called  the  coefficient  of  decomposition ,  the  law  of  the  reaction 
is,  that  the  sum  of  the  coefficients  of  decomposition  in  the 
two  cases  is  always  equal  to  100.  For  example :  if  1  at. 
sulphate  of  potash  and  1  at.  acetate  of  soda  act  upon  each 
other,  and  -^-^^  of  the  original  quantity  of  sulphate  of  potash 
remain  in  solution  as  such,  the  coefficient  of  decomposition  is 
36.  The  numerical  values  of  the  coefficients  of  decomposi- 
tion, determined  in  several  cases  by  the  method  above  de- 
scribed, are  given  in  the  following  table  :  — 


Salts. 

Acetate  of  potash  . 
Nitrate  of  lead    .     . 

Chloride  of  potassium 
Sulphate  of  zinc  .     . 

Acetate  of  baryta  . 
Nitrate  of  lead    ,     . 

Chloride  of  sodium  . 
Sulphate  of  zinc .  . 
Acetate  of  baryta  . 
Nitrate  of  potash  . 
Acetate  of  potash  . 
Nitrate  of  strontia  . 
Acetate  of  strontia  . 
Nitrate  of  lead   .     . 

Acetate  of  potash  . 
Sulphate  of  soda 

Chloride  of  potassium 
Manganous  sulphate 
Chloride  of  potassium 
Sulphate  of  magnesia 
Chloride  of  sodium 
Sulphate  of  magnesia 


Coefficient  of 
Decom- 
position. 

920 
84-0 
77-0 
72-0 
72-0 
67-0 
65  5 
62-0 
58-0 
56-0 
54  5 


Salts. 

Acetate  of  lead  . 
Nitrate  of  potash 

Chloride  of  zinc  . 
Sulphate  of  potash 

Acetate  of  lead  . 
Nitrate  of  baryta 

Chloride  of  zinc  . 
Sulphate  of  soda 

Acetate  of  potash 
Nitrate  of  baryta 

Acetate  of  stronti  i 
Nitrate  of  potash 

Acetate  of  lead  . 
Nitrate  of  strontia 

Acetate  of  soda  . 
Nitrate  of  potash 
Mangiinous  chloride 
Sulphate  of  potash 

Chloride  of  magnesium  "^ 
Sulphate  of  potash 

Chloride  of  magnesium 
Sulphate  of  soda 


Coefficient  of 
Decom- 
position. 

90 
17-6 
22-0 
29-0 
27-0 
36-0 
33  0 
36-5 
42-5 
43-0 
45-8 


In  all  these  cases,  except  one,  the  coefficients  of  decompo- 
sition are  greatest  when  the  strongest  acid  and  the  strongest 
base  are  not  originally  united  in  the  same  salt.  The  ex- 
ceptional  case  is  presented  by  the  mixture  of  nitric  acid. 


596  CHEMICAL   AFFINITY. 

acetic  acid,  potash,  and  baryta,  in  which  the  greatest  co- 
efficient of  decomposition  is  obtained  when  the  nitric  acid  is 
at  first  united,  not  with  the  baryta,  but  with  the  potash.  A 
similar  result  was  obtained  by  the  action  of  potash  on  nitrate 
of  baryta  and  of  baryta  on  nitrate  of  potash,  wood-spirit 
being  used  as  ther  precipitating  agent  instead  of  alcohol.  The 
coefficient  of  decomposition  was  6*9  in  the  former  case,  and 
93-6  in  the  latter. 

It  is  not  easy  to  determine  how  far  the  particular  numerical 
results  of  these  experiments  were  influenced  by  the  presence 
of  the  alcohol ;  but  as  its  action  was  the  same  in  both  cases 
of  each  pair  of  experiments,  the  results  certainly  justify  the 
conclusion  that  the  two  salts,  when  mixed,  resolve  themselves 
into  four ;  that  the  partition  takes  place  in  a  definite  manner ; 
and  that  the  proportions  of  the  resulting  salts  are  independent  of 
the  manner  in  which  their  elements  were  originally  combined. 

Experiments  bearing  on  the  same  point,  have'  also  been 
published  by  Margueritte  *,  who  finds  that  two  salts  in  solu- 
tion mutually  decompose  each  other,  even  when  one  of  them 
is  already  the  least  soluble  of  the  four  salts  that  may  be  pro- 
duced from  the  two  acids  and  the  two  bases  present.  A 
saturated  solution  of  chlorate  of  potash,  to  which  chloride  of 
sodium  is  added,  becomes  capable  of  dissolving  an  additional 
quantity  of  chlorate  of  potash,  showing  that  a  portion  of  the 
chlorate  has  been  decomposed,  and  a  more  soluble  salt  formed. 
Chloride  of  ammonium  is  precipitated  from  its  saturated 
aqueous  solution  on  addition  of  a  small  quantity  of  nitrate  of 
ammonia;  but  the  previous  addition  of  chlorate  of  potash 
prevents  the  precipitation ;  whence  it  would  appear  tliat  the 
chlorate  of  potash  and  chloride  of  ammonium  are  partially  con- 
verted into  chlorate  of  ammonia  and  chloride  of  potassium. 
The  precipitation  of  sulphate  of  lime  from  its  aqueous  solu- 
tion by  alcohol,  is  prevented  by  the  presence  of  the  nitrates 

♦  Compt.  rend  xxxviii.  304. 


CHEMICAL   AFFINITY.  597 

or  chlorides  of  potassium,  sodium,  or  ammonium,  evidently 
because  a  portion  of  the  sulphate  is  converted  into  nitrate  or 
chloride.  A  solution  of  chloride  of  ammonium  dissolves  the 
carbonates  of  baryta,  strontia,  and  lime  more  readily  than 
pure  water,  because  it  partially  converts  them  into  chlorides, 
the  liquid  at  the  same  time  acquiring  an  alkaline  reaction,  in 
consequence  of  the  formation  of  carbonate  of  ammonia. 

The  decomposition  of  insoluble  by  soluble  salts  affords  a 
striking  instance  of  the  tendency  of  atoms  to  interchange,  and 
of  the  influence  of  mass  on  chemical  action.  According  to 
H.  Rose*,  sulphate  of  baryta  is  completely  decomposed  by 
boiling  with  solutions  of  alkaline  carbonates,  provided  that 
each  equivalent  of  sulphate  of  baryta  is  acted  upon  by  at 
least  15  eq.  of  the  alkaline  carbonate.  If  1  eq.  of  sulphate 
of  baryta  is  boiled  with  only  1  eq.  of  carbonate  of  potash, 
only  J-  of  it  is  decomposed,  and  only  -^  by  boiling  with  1  eq. 
of  carbonate  of  soda,  further  decomposition  being  prevented 
by  the  presence  of  the  alkaline  sulphate  already  formed.  If, 
however,  the  liquid  be  decanted  after  a  while,  the  residue 
boiled  with  a  fresh  portion  of  the  alkaline  carbonate,  and 
these  operations  repeated  several  times,  complete  decomposi- 
tion is  effected.  Carbonate  of  baryta  is  converted  into  sul- 
phate by  the  action  of  an  aqueous  solution  of  sulphate  of 
potash  or  soda,  even  at  ordinary  temperatures.  Solution  of 
carbonate  of  ammonia  does  not  decompose  sulphate  of  baryta 
either  at  ordinary  or  at  higher  temperatures ;  carbonate  of 
baryta  is  not  decomposed  by  sulphate  of  ammonia  at  ordinary 
temperatures,  but  easily  on  boiling.  Sulphate  of  baryta  is 
not  decomposed  by  boiling  with  caustic  potash-solution,  pro- 
vided the  carbonic  acid  of  the  air  be  excluded ;  but  by  fusion 
with  hydrate  of  potash,  it  is  decomposed,  with  formation  of 
carbonate  of  baryta,  because  the  carbonic  acid  of  the  air 
cannot  then   be   completely   excluded.      Hydrochloric   and 

*  Pogg.  Ann.  xciv.  481  ;  xcv.  96,  284. 
VOL.  II.  T  T 


598  CHEMICAL   AFFINITY. 

nitric  acids,  left  in  contact  at  ordinary  temperatures  with 
sulphate  of  baryta,  either  crystallised  or  precipitated,  dissolve 
only  traces  of  it;  at  the  boiling  heat,  a  somewhat  larger 
quantity  is  dissolved,  and  the  solution  forms  a  cloud,  both 
with  a  dilute  solution  of  chloride  of  barium  and  with  dilute 
sulphuric  acid.  Sulphate  of  strontia  is  dissolved  by  hydro- 
chloric acid  at  ordinary  temperatures,  sufficiently  to  form  a 
slight  precipitate  with  dilute  sulphuric  acid,  and  with  chloride 
of  strontium.  Sulphate  of  lime  treated  with  hydrochloric 
acid,  either  cold  or  boiling,  yields  a  liquid  in  which  a  preci- 
pitate is  formed,  after  a  while,  by  dilute  sulphuric  acid,  but 
not  by  chloride  of  calcium. 

Sulphate  of  strontia  and  sulphate  of  lime  are  completely 
decomposed  by  solutions  of  the  alkaline  carbonates  and  bi- 
carbonates  at  ordinary  temperatures,  and  more  quickly  on 
boiling,  even  if  considerable  quantities  of  an  alkaline  sulphate 
are  added  to  the  solution :  the  decomposition  is  also  effected 
by  carbonate  of  ammonia,  even  at  ordinary  temperatures. 
The  carbonates  of  strontia  and  lime  are  not  decomposed  by 
solutions  of  the  sulphates  of  potash  or  soda  at  any  tempera- 
ture ;  sulphate  of  ammonia  does  not  decompose  them  at  ordi- 
nary temperatures,  but  readily  with  the  aid  of  heat. 

Sulphate  of  lead  is  completely  converted  into  carbonate  by 
solutions  of  the  alkaline  carbonates  and  bicarbonates,  even  at 
ordinary  temperatures,  the  neutral  carbonates,  but  not  the 
bicarbonates,  then  dissolving  small  quantities  of  oxide  of  lead. 
Carbonate  of  lead  is  not  decomposed  by  solutions  of  the  alka- 
line sulphates,  either  at  ordinary  temperatures  or  on  boiling. 

Chromate  of  baryta  is  decomposed  at  ordinary  tempe- 
ratures by  solutions  of  the  neutral  alkaline  carbonates,  and 
much  more  easily  by  boiling  with  excess  of  an  alkaline 
bicarbonate.  When  equivalent  quantities  of  the  chromate  of 
baryta  and  carbonate  of  soda  are  boiled  with  water,  ^  of  the 
whole  is  decomposed ;  when  the  same  quantities  of  the  salts 


CHEMICAL   AFFINITY.  599 

are  fused  together,  and  the  mass  treated  with  water,  only  -^ 
of  the  baryta-salt  is  decomposed.  Carbonate  of  baryta  is 
completely  converted  into  chromate  by  digestion  with  a  solu- 
tion of  an  alkaline  monochromate ;  and  the  decomposition  of 
chromate  of  baryta  by  alkaline  carbonates,  even  at  the  boiling 
heat,  is  completely  prevented  by' the  presence  of  a  certain 
quantity  of  an  alkaline  monochromate. 

Seleniate  of  baryta  is  easily  and  completely  decomposed  by 
solutions  of  alkaline  carbonates,  even  at  ordinary  tempe- 
ratures: this  salt  is  somewhat  soluble  in  water,  and  more 
readily  in  dilute  acids. 

Oxalate  of  lime  is  decomposed  by  alkaline  carbonates  even 
at  ordinary  temperatures ;  but  to  effect  complete  decompo- 
sition the  liquid  must  be  frequently  decanted  and  renewed. 
The  decomposition  takes  place  rapidly  at  the  boiling  heat; 
but  in  all  cases  it  is  completely  prevented  by  the  presence  of 
a  certain  quantity  of  a  neutral  alkaline  oxalate.  When  the 
salts  are  mixed  in  equivalent  proportions,  ^  of  the  oxalate  of 
lime  are  decomposed  at  ordinary  temperatures,  and  ^  on 
boiling.  Carbonate  of  lime  is  partially  converted  into  oxalate 
by  the  action  of  a  solution  of  neutral  oxalate  of  potash  at 
ordinary  temperatures,  and  more  quickly  on  boiling; — but 
the  decomposition  is  never  complete,  even  when  the  liquid  is 
frequently  decanted  and  renewed. — Oxalate  of  lead  is  com- 
pletely converted  into  carbonate  at  ordinary  temperatures  by 
the  solution  of  an  alkaline  carbonate,  a  small  portion  of  the 
carbonate  of  lead  dissolving  in  the  liquid.    (Rose.) 

The  preceding  experiments  exhibit  in  a  striking  manner 
the  influence  of  difference  of  solubility  in  determining  the 
order  of  decomposition.  Sulphate  of  baryta  is  less  soluble 
than  the  carbonate,  and,  accordingly,  carbonate  of  baryta  is 
more  readily  decomposed  by  alkaline  sulphates,  than  the 
sulphate  by  alkaline  carbonates.  Precisely  the  contrary 
relations  are  exhibited  by  the  sulphates  and  carbonates  of 

T  T    2 


600  CHEMICAL   AFFINITY. 

strontia*  and  lime,  both  as  regards  solubility  and  order  of 
decomposition.  On  the  other  hand,  oxalate  of  lime  is  less 
soluble  than  the  carbonate,  and  yet  its  decomposition  by 
alkaline  carbonates  takes  place  more  easily  than  the  opposite 
reaction :  in  this  case,  the  order  of  decomposition  appears 
rather  to  be  determined,  as  in  Malaguti's  experiments,  by  the 
tendency  of  the  strongest  acid  to  unite  with  the  strongest  base. 
The  effect  of  a  soluble  sulphate,  &c.,  in  arresting  the  de- 
composition of  the  corresponding  insoluble  salts  by  alkaline 
carbonates,  is  evidently  due  to  its  tendency  to  produce  the 
reverse  action :  hence  the  acceleration  produced  by  decanting 
and  renewing  the  liquid.  Some  insoluble  salts,  however,  phos- 
phate of  lime  for  example,  are  never  completely  decomposed, 
even  by  this  treatment. 

The  constant  tendency  to  interchange  of  atoms,  exhibited 
in  the  phenomena  above  described,  and,  indeed,  in  all  cases 
of  chemical  action,  suggests  the  idea  that  the  atoms  of  all 
bodies,  at  least  in  the  fluid  state,  are  in  constant  motion. 
We  have  already  seen  that  the  same  idea  is  suggested  by  the 
phenomena  of  heat,  and  leads  to  a  consistent  theory  of  those 
phenomena  (II.  449).  On  a  similar  hypothesis.  Professor 
Williamson  proposes  to  construct  a  general  theory  of  chemical 
action.f  The  fundamental  notion  of  this  theory  is,  that  the 
atoms  of  all  compounds,  whether  similar  or  dissimilar,  are 
continually  changing  places,  the  interchange  taking  place 
more  readily  as  the  atoms  resemble  each  other  more  closely. 
Thus,  in  a  mass  of  hydrochloric  acid,  each  atom  of  hydrogen 
is  supposed,  not  to  remain  quietly  in  juxta-position  with  the 
atom  of  chlorine  with  which  it  happens  to  be  first  united,  but 
to  be  continually  changing  places  with  other  atoms  of  hydro- 
gen, or,  what  comes  to  the  same  thing,  continually  becoming 
associated  with  other  atoms  of  chlorine.     This  interchange  is 

*  According  to  Fresenius,  carbonate  of  strontia  dissolves  in  11,862  parts,  and 
the  sulphate  in  6895  parts  of  cold  water, 
t  Chem.  Soc.  Qii.  J.,  ix.  110. 


CHEMICAL   AFFINITY.  601 

not  perceptible  to  the  eye,  because  one  molecule  of  hydro- 
chloric acid  is  exactly  like  another.  But  suppose  the  hydro- 
chloric acid  to  be  mixed  with  a  solution  of  sulphate  of  copper 
(the  component  atoms  of  which  are  likewise  undergoing  a 
change  of  place),  the  basylous  elements,  hydrogen  and  copper, 
then  no  longer  limit  their  change  of  place  to  the  circle  of 
atoms  with  which  they  were  at  first  combined,  but  the  hy- 
drogen and  copper  likewise  change  places  with  each  other, 
forming  chloride  of  copper  and  sulphuric  acid.  Thus  it  is 
that,  when  two  salts  are  mixed  in  solution,  and  nothing 
separates  out  in  consequence  of  their  mutual  action,  the  bases 
are  divided  between  the  acids,  and  four  salts  are  produced. 
If,  however,  the  analogous  elements  of  the  two  compounds 
are  very  dissimilar,  and,  consequently,  interchange  but  slowly, 
it  may  happen  that  the  stronger  acid  and  the  stronger  base 
remain  almost  entirely  together,  leaving  the  weaker  ones 
combined  with  each  other.  This  is  strikingly  seen  in  a  mix- 
ture of  sulphuric  acid  (sulphate  of  hydrogen)  and  borate  of 
soda,  which  soon  becomes  almost  w^holly  converted  into  sul- 
phate of  soda  and  free  boracic  acid  (borate  of  hydrogen). 

Now  suppose  that,  instead  of  sulphate  of  copper,  sulphate  of 
silver  is  added  to  the  hydrochloric  acid.  At  the  first  moment 
the  interchange  of  elements  may  be  supposed  to  take  place 
as  above,  and  the  four  compounds,  -SO^Hg,  SO^Agg,  CIH, 
and  ClAg,  to  be  formed ;  but  the  last,  being  insoluble,  is 
immediately  removed  by  precipitation ;  the  remaining  ele- 
ments then  act  upon  each  other  in  the  same  way,  and  this 
action  goes  on  till  all  the  chlorine  or  all  the  silver  is  removed 
in  the  form  of  chloride  of  silver  ;  if  the  original  compounds  are 
mixed  in  exactly  equivalent  proportions,  the  final  result  is 
the  formation  of  only  two  salts,  viz.,  in  this  case,  -^04112  and 
ClAg.  A  similar  result  is  produced  when  one  of  the  pro- 
ducts of  the  decomposition  is  volatile  at  the  existing  tempera- 
ture, as  when  hydrate  or  carbonate  of  soda  is  boiled  with 
chloride  of  ammonium. 

tt  3 


602  CHEMICAL  AFFINITY. 

This  theory  affords  a  simple  explanation  of  the  action  of 
sulphuric  acid  upon  alcohol,  whereby  sulphovinic  acid 
(sulphate  of  ethyl  and  hydrogen)  is  first  formed,  and  after- 
wards, at  a  certain  temperature,  ether  and  water  are  elimi- 
nated (I.  226).     When  alcohol,  ^^^^j  O,  and  sulphuric  acid, 

XT 

XT }  ^^4,  are  mixed  together,  the  interchange  between  the 

atoms  of  ethyl  in  the  former  and  of  hydrogen  in  the  latter 
gives  rise  to  the  formation  of  sulphovinic  acid  and  water : — 

But  the  change  does  not  stop  here,  for  the  sulphovinic  acid 
thus  produced,  meeting  with  fresh  molecules  of  alcohol, 
exchanges  its  ethyl  for  the  hydrogen  of  the  alcohol,  producing 
ether  and  sulphuric  acid : — 

The  sulphuric  acid  is  thus  restored  to  its  original  state,  and 
is  ready  to  act  upon  fresh  quantities  of  alcohol ;  so  that  if 
alcohol  be  allowed  to  run  into  the  mixture  in  a  constant 
stream,  the  temperature  being  kept  within  certain  limits 
(between  140°  and  160°  C),  the  process  goes  on  without  in*- 
terruption,  ether  and  water  continually  distil  over,  and  the 
same  quantity  of  sulphuric  acid  suffices  for  the  etherification 
of  an  unlimited  quantity  of  alcohol.  This  is  the  peculiarity 
of  the  process  ;  it  has  given  rise  to  a  variety  of  explanations ; 
in  fact,  the  process  of  etherification  has  long  been  a  battle- 
ground of  chemical  theories.*  The  discussion  of  these  various 
theories  would  be  foreign  to  the  present  purpose ;  it  is  suffi- 
cient to  remark  that  the  hypothesis  of  atomic  interchange 
aff'ords  a  ready  explanation  of  the  most  obscure  point  in  the 

*  See  the  translation  of  Gmelin's  Handbook,  vol.  viii.  pp.  231—237. 


CHEMICAL   AFFINITY.  603 

reaction,  viz.,  the  formation  and  decomposition  of  sulphovinic 
acid  following  each  other  continuously,  without  any  change 
of  temperature  or  other  determining  cause.  If  it  be  admitted 
that  the  atoms  of  ethyl  and  hydrogen  in  the  mixture  are  con- 
tinually interchanging  in  all  possible  ways,  this  series  of  alter- 
nate actions  follows  as  a  necessary  consequence. 

The  formation  of  ether  by  the  mutual  action  of  sulphovinic 
acid  and  alcohol  is  also  analogous  to  its  production  by  the 
action  of  iodide  of  ethyl  on  potassium-alcohol  (p.  534) : — 

^aHsjo  +  ^^H.I  =  J^H^ja  +  KI. 

The  same  view  is  corroborated  by  the  fact  recorded  by  Wil- 
liamson, in  the  paper  above  quoted,  that  sulphamylic  acid 
(sulphate  of  amyl  and  hydrogen)  distilled  with  common 
alcohol,  yields  an  ether  containing  both  ethyl  and  amyl : — 

%^^^,  +  %'}G^ = §i;jo + |]sa, ; 

and  that  the  same  compound  is  obtained  by  distilling  a  mix- 
ture of  vinic  and  amylic  alcohols  with  sulphuric  acid ;  also 
with  the  fact  discovered  by  Chancel,  that  sulphovinate  of 
potassium  distilled  with  potassium-alcohol,  yields  ether : — 


K 


]^^4  +      ^K^}^  ""  QJlJ^  "^  k]'^*^4; 


and  that  the  same  salt  distilled  with  methylate  of  potassium, 
^HgKO,  yields  methamylic  ether,  jno^]"^* 

3 

The  idea  of  atomic  motion  is  in  accordance  with  physical  as 
well  as  chemical  phenomena.  To  suppose  that  rest,  rather 
than  motion,  is  the  normal  state  of  the  particles  of  matter, 
is  at  variance  with  all  that  we  know  of  the  effects  of 
light,  heat,  and  electricity.  In  the  heat-theory  of  Clausius, 
(II.  449),  the  particles  of  bodies  are  supposed  to  be  affected 

T  T    4 


604  DIFFUSION    OF    LIQUIDS. 

with  progressive,  as  well  as  with  rotatory  and  vibratory  move- 
ments ;  and  this  same  hypothesis  of  progressive  movement 
which,  of  course,  implies  change  of  relative  position  among 
the  particles,  affords,  as  already  stated,  a  ready  explanation 
of  certain  chemical  reactions,  otherwise  somewhat  obscure. 
It  is  worth  while  to  observe  that,  in  the  heat-theory  of 
Clausius,  the  progressive  motion  of  the  particles  is  supposed 
to  exist  only  in  the  liquid  and  gaseous  states,  the  particles  of 
solid  bodies  merely  performing  rotatory  and  vibratory  move- 
ments about  certain  positions  of  equilibrium.  This  is  quite 
in  accordance  with  the  well-known  fact  that  chemical  reaction 
rarely  takes  place  between  solid  bodies. 


DIFFUSION  OF  LIQUIDS. 

Intimately  connected  with  the  interchange  of  atoms  re- 
sulting in  chemical  decomposition,  is  the  process  by  which  a 
saline,  or  other  soluble  substance,  is  spread  or  diffused  uni- 
formly through  the  mass  of  the  solvent ;  in  some  cases,  in- 
deed, as  will  presently  be  seen,  the  decomposition  of  salts  is 
greatly  facilitated  by  the  tendency  of  one  or  more  of  the 
products  of  decomposition  to  diffuse  into  the  surrounding 
liquid. 

The  phenomena  of  liquid  diffusion  have  been  minutely 
investigated  by  Mr.  Graham.*  The  apparatus  used  consisted 
of  a  set  of  phials,  of  nearly  equal  capacity,  cast  in  the  same 
mould,  and  further  adjusted  by  grinding  to  a  uniform  size 
of  aperture.  The  phials  were  3-8  inches  high,  with  a  neck 
0*5  inch  in  depth,  and  aperture  1*25  inch  wide;  capacity  to 
base  of  neck  equal  to  2080  grains  of  water,  or  between 
4  and  5  ounces.     For  each  diffiision-pliial,  a  plain  glass  ivatev" 

*  Phil.  Trans.  1850,  pp.  1,  805  ;  Chem.  Soc.  Qu.  J.  ii.  60,  257  ;  iv,  83. 


DIFFUSION   OF   LIQUIDS. 


605 


jar  was  also  provided,  4  inches  in  diameter  and  7   inches 
deep.     (Fig.  43). 

The  difFusion-phial  was  filled  with  the  saline 
solution,  sal-ammoniac  for  instance,  to  the  base 
of  the  neck,  or  more  correctly  to  a  distance  of 
0*5  inch  from  the  ground  surface  of  the  lip. 
The  neck  of  the  phial  was  then  filled  up  with 
distilled  water,  a  light  float  being  first  placed 
on  the  surface  of  the  solution,  and  care  being 
taken  to  avoid  agitation.  After  the  phial  had 
been  placed  within  the  jar,  water  was  poured  into  the  jar, 
so  as  to  cover  the  open  phial  to  the  depth  of  an  inch 
which  required  about  20  ounces  of  water.  The  saline  liquid 
in  the  phial  is  thus  allowed  to  communicate  freely  with  the 
water  in  the  jar.  The  diffusion  is  interrupted  by  placing 
a  small  plate  of  ground  glass  on  the  mouth  of  the  phial, 
and  raising  the  latter  out  of  the  jar.  The  amount  of  salt 
diffused,  called  the  diffusion-product,  or  diffusaie,  is  ascertained 
by  evaporating  the  water  in  the  jar  to  dryness,  or,  in  the 
case  of  chlorides,  by  precipitating  with  nitrate  of  silver. 

The  results  of  several  series  of  experiments  made  in  this 
manner  are  given  in  the  following  Table,  the  second  column 
of  which  shows  the  quantity  of  salt  in  100  parts  of  the  solu- 
tion ;  the  third,  the  time  of  diffusion ;  the  fourth,  the  tempe- 
rature, on  the  Fahrenheit  scale ;  the  fifth,  the  quantity  of  salt 
diffused :  — 


606 


DIFFUSION   OF   LIQUIDS. 


Diffusion  of  Saline  Solutions. 


Substance. 

Per  Cent. 

Days. 

Fahr. 

Diffusate. 

r 

1 

5 

51° 

7-41 

2 

5 

51 

15-04 

Hydrochloric  acid    . 

2 

5 

59-7 

16-55 

4 

5 

51 

30-72 

I 

8 

5 

51 

67-68 

Hydriodic  acid 

2 

5 

51 

1511 

Hydrobromic  acid   . 

2 

6 

59-7 

16-58 

Bromine 

0-864 

10 

60-1 

5-84 

Hydrocyanic  acid    . 

1-766 

5 

64-2 

11-68 

1 

5 

51-2 

6-99 

Hydrated  nitric  acid  (NO^H)  .  • 

2 

4 

5 
5 

51-2 
51-2 

14-74 
28-76 

8 

5 

51-2 

57-92 

r 

1 

10 

49-7 

8-69 

Hydrated  sulphuric  acid  (SO4H) 

2 

4 

10 
10 

49-7 
49-7 

16-91 
33-89 

8 

10 

49-7 

68-96 

Chromic  acid  .... 

1-762 

10 

67-3 

19-78 

2 

10 

48-8 

11-31 

Acetic  acid  (C^H^OJ      . 

4 

10 

48-8 

22-02 

8 

10 

48-8 

41-80 

1 

10 

68-1 

8-09 

Sulphurous  acid 

2 

4 

10 
10 

68-1 
68-1 

16-96 
33-00 

8 

10 

68-1 

66-38 

1 

4-04 

63-4 

4-93 

Ammonia         .        .        .        .  < 

2 

4 

4-04 
4-04 

63-4 
63-4 

9*59 
19-72 

8 

4-04 

63-4 

41-22 

2 

10 

48-7 

8-62 

Alcohol ■ 

4 

10 

48-7 

16-12 

8 

10 

48-7 

35-50 

1 

11-43 

64-1 

7-72 

Nitrate  of  baiyta 

2 

4 

11-43 
11-43 

64-1 
64-1 

15-04 
29-60 

8 

11-43 

64-1 

54-50 

Nitrate  of  strontia   . 

0-82 

11-43 

51-5 

5-59* 

1 

11-43 

64-1 

7-66 

Nitrate  of  lime 

2 

4 

11-43 
11-43 

64-1 
64-1 

15-01 
29-04 

8 

11-43 

64-1 

55-10 

Acetate  of  baryta     . 

1 

16-17 

53-5 

7-50 

Acetate  of  lead 

1 

16-17 

53-1 

7-84 

1 

8-57 

6-3 

6-32 

Chloride  of  barium  . 

2 
4 

8-57 
8-57 

6-3 
6-3 

12-07 
23-96 

8 

8-57 

6-3 

45-92 

1 

8-57 

6-3 

6-09 

Chloride  of  strontium 

2 
4 

8-57 
8-57 

6-3 
6-3 

11-66 
23-56 

8 

8-57 

6-3 

44-46 

DIFFUSION   OF   LIQUIDS. 
Diffusion  of  Salike  Solvtio^b  —  continued. 


607 


Substance. 

Per  Cent. 

Days. 

Fahr. 

Diffusate. 

r 

1 

11-43 

63-8° 

7-92 

2 

11'43 

63-8 

15-35 

Chloride  of  calcium 

4 

11-43 

63-8 

30-78 

8 

11-43 

63-8 

61-56 

1 

11-43 

50-8 

6-51 

Chloride  of  manganese     . 

1 

11-43 

50-8 

6-63 

Nitrate  of  magnesia 

1 

11-43 

50-8 

6-49 

Nitrate  of  copper     . 

1 

11-43 

50-8 

6-44 

Chloride  of  zinc 

1 

11-43 

50-8 

6-29 

Chloride  of  magnesium    . 

1 

11-43 

50-8 

6-17 

Cupric  chloride 

1 

11-43 

50-8 

6-06 

Ferrous  chloride 

1 

11-43 

53-5 

6-30 

/ 

1 

16-17 

65-4 

7-31 

2 

16-17 

65-4 

12-79 

\ 

4 

16-17 

65-4 

23-46 

Sulphate  of  magnesia       .        .  < 

8 

16-17 

65-4 

42-82 

1 

8 

16-17 

62-8 

42-66 

16 

16-17 

62-8 

75-06 

\ 

24 

16-17 

62-8 

102-04 

/ 

1 

16-17 

65-4 

6-67 

/ 

2 

16-17 

65-4 

12-22 

1 

4 

16-17 

65-4 

23-12 

Sulphate  of  zinc       .        .       .  < 

8 

16-17 

65-4 

42-26 

i 

8 

16-17 

62-8 

39-62 

f 

16 

16-17 

62-8 

74-40 

V 

24 

16-17 

62-8 

101-42 

' 

1 

16-17 

65-4 

5-48 

Sulphate  of  alumina. 

2 
4 

16-17 
16-17 

65-4 
65-4 

10-21 
19-28 

8 

16-17 

65-4 

33-52 

r 

2 

7 

63-4 

13-61 

Nitrate  of  silver 

4 

7 

63-4 

26-34 

8 

7 

63-4 

51-88 

■ 

2 

7 

63-4 

12-35 

Nitrate  of  soda 

4 

7 

63-4 

23-56 

8 

7 

63'4 

47-74 

' 

1 

7 

63-4 

6-32 

2 

7 

63-4 

12-37 

Chloride  of  sodium  . 

4 

7 

63-4 

24-96 

8 

7 

63-4 

48-44 

2 

7 

63-4 

12-14 

Iodide  of  sodium 

2 

7 

59-8 

12-18 

Bromide  of  sodium  . 

2 

7 

59-8 

12-14 

Chloride  of  potassium 

2 

5-716 

59-8 

12-24 

Bromide  of  potassium 

2 

5-716 

59-8 

12-46 

Iodide  of  potassium 

2 

5-716 

59-8 

12-51 

Chloride  of  ammonium     . 

1 

5-716 

59-8 

5-99 

" 

1 

8-08 

68-2 

7-23 

Bicarbonate  of  potash 

2 
4 

8-08 
8-08 

68-2 
68-2 

14-05 
26-72 

8 

8-08 

68-2 

52-01 

Bicarbonate  of  ammonia  .        .  ■ 

1 
2 

8-08 
8-08 

68-2 
68-2 

6-91 
13-65 

608  DIFFUSION   OF   LIQUIDS. 

Diffusion  of  Saline  Solutions  —  continued. 


Substance. 

Per  Cent. 

Days. 

Fahr. 

Diffusate. 

Bicarbonate  of  ammonia  . 

4 

8 

8-08 
8-08 

68-2° 
68-2 

27-00 
50-10 

1 

9-87 

68-2 

7-31 

Bicarbonate  of  soda         .        .  ■ 

2 
4 

9-87 
9-87 

68-2 
68-2 

13-81 
26-70 

8 

9-87 

68-2 

52-38 

1 

4-04 

63-3 

6-56 

Hydrate  of  potash    . 

2 
4 

4-04 
4-04 

63-3 
63-3 

12-84 
25-04 

8 

4-04 

63-3 

52-24 

" 

1 

4-95 

632 

5-81 

Hydrate  of  soda, 

2 
4 

4-95 
4-95 

63-2 
63-2 

11-09 
20-86 

8 

4-95 

63-2 

40-44 

I 

8-08 

63-6 

6-13 

Carbonate  of  potash 

2 
4 

8-08 
8-08 

63-6 
63-6 

11-92 

22-88 

8 

8-08 

63-6 

45-44 

1 

9-9 

63-4 

6-02 

Carbonate  of  soda    . 

2 
4 

9-9 
9-9 

63-4 
63-4 

11-70 
21-42 

8 

9-9 

63-4 

39-74 

Sulphate  of  potash  . 

1 

8-08 

60-2 

6-16 

2 

8-08 

60-2 

11-60 

4 

8-08 

60-2 

22-70 

8 

8-08 

60-2 

43-92 

' 

1 

9-9 

59-9 

6-33 

Sulphate  of  soda 

2 

4 

9-9 
9-9 

59-9 
59-9 

12-00 
21-96 

8 

9-9 

59-9 

41-38 

Sulpliite  of  potash    . 

2 

808 

59-5 

11-63 

Sulphite  of  soda 

2 

9-9 

59-5 

11-83 

Hyposulphite  of  potash    . 

2 

8-08 

59-7 

12-37 

Hyposulphite  of  soda 

2 

9-9 

59-9 

11-89 

Sulphovinate  of  potash     . 

2 

8-08 

59-7 

12-60 

Sulphovinate  of  soda 

2 

9-9 

59-5 

13-03 

r 

1 

8-08 

.59-9 

6-20 

Oxalate  of  potash     .        .        .  </ 

2 
4 

8-08 
8-08 

59-9 
59-9 

1217 
23-04 

l 

8 

8-08 

59-9 

42-82 

Oxalate  of  soda 

1 

9-9 

59-9 

6-24 

r 

1 

8-08 

60-2 

6-44 

Acetate  of  potash     .        .        .J 

2 
4 

8-08 
8-08 

60-2 
60-2 

12-52 
23-44 

L 

8 

8-08 

60-2 

47-26 

1 

9-9 

59-5 

6-67 

Acetate  of  soda        .        .        .  < 

2 

4 

9-9 
9-9 

59-5 
.59-5 

12-46 
25-04 

8 

9-9 

59-5 

48-04 

Tartrate  of  potash    . 

2 

8'08 

59-9 

10-96 

Tartrate  of  soda 

2 

9-9 

59-5 

10-65 

Hydrochlorate  of  morphine 

2 

11-43 

64-1 

11-60 

Hydrochlorate  of  strychnine    . 

2 

11-43 

64-1 

11-49 

DIFFUSION   OF   LIQUIDS.  609 

These  experiments,  and  a  number  of  others  made  in  a 
similar  manner,  lead  to  the  following  general  conclusions :  — 

1.  Different  salts,  in  solutions  of  equal  strength,  diffuse 
unequally  in  equal  times. 

2.  With  each  salt,  the  rate  of  diffusion  increases  with  the 
temperature,  and  at  any  given  temperature,  is  proportionate 
to  the  strength  of  the  solution,  at  least  when  the  quantity  of 
salt  dissolved  does  not  exceed  4  or  5  per  cent. 

3.  There  exist  classes  of  equidiffusive  substances  which 
coincide  in  many  cases  with  the  isomorphous  groups,  but  are, 
on  the  whole,  more  comprehensive  than  the  latter.  Thus,  the 
same  rate  of  diffusion  is  exhibited  by  hydrochloric,  hydro- 
bromic,  and  hydriodic  acid ;  by  the  chlorides,  iodides,  and 
bromides  of  the  alkali-metals;  by  the  nitrates  of  baryta, 
strontia,  and  lime ;  the  sulphates  of  magnesia  and  zinc, 
&c.  &c. 

4.  For  several  groups  of  salts  it  is  found  that  the  squares 
of  the  times  of  equal  diffusion,  from  solutions  of  the  same 
strength,  stand  to  one  another  in  a  simple  numerical  relation. 
Thus,  the  diffusate  from  a  solution  of  nitrate  of  potash,  in 
7  days,  was  equal  to  that  obtained  from  an  equally  strong  solu- 
tion of  carbonate  of  potash,  in  9*9  days,  numbers  which  are  to 
one  another  as  1 :  v  2.  Similar  results  were  obtained  with  2  per 
cent,  solutions  of  nitrate  and  sulphate  of  potash,  equal  dif- 
fusates  of  the  two  being  obtained  in  3*5  and  4*95  days,  in  7 
and  9*9  days,  and  in  10*5  and  14*85  days;  also,  with  hydrate 
and  nitrate  of  potash,  and  with  nitrate  and  carbonate  of  soda. 
The  times  of  equal  diffusion  of  1  per  cent,  solutions  of 
chloride  of  ammonium  and  chloride  of  sodium,  were  to  one 
another  as  V2  :  VS.  Now,  according  to  Mr.  Graham's  ex- 
periments (  I.  87),  the  squares  of  the  times  of  equal  diffusion 
of  gases  are  to  one  another  in  the  ratio  of  their  densities. 
Hence,  by  analogy,  it  may  be  inferred  that  the  molecules  of 
these  several  salts,  as  they  exist  in  solution,  possess  densities 
which  are  to  one  another  as  the  squares  of  the  times  of  equal 


610  DIFFUSION  OP   LIQUIDS. 

diffusion.  Thus,  the  solution- densities  of  sulphate,  nitrate, 
and  hydrate  of  potash,  are  to  one  another  as  the  numbers  4, 
2,  and  1.  These  solution-densities  appear  to  relate  to  a  kind 
of  molecules  different  from  the  chemical  atoms,  and  the 
weights  of  which  are  either  equal,  or  bear  to  one  another  a 
simple  numerical  relation. 

The  diffusion  of  a  salt  into  the  solution  of  another  salt 
takes  place  with  nearly  the  same  velocity  as  into  pure  water ; 
at  least,  when  the  solutions  are  dilute.  Mr.  Graham  has 
shown  that  the  diffusion  of  a  4  per  cent,  solution  of  carbonate 
of  soda,  is  not  sensibly  affected  by  the  presence  of  4  per  cent, 
of  sulphate  of  soda  in  the  liquid  atmosphere ;  nor  that  of  a 
4  per  cent,  solution  of  nitrate  of  potash,  by  the  same  propor- 
tion of  nitrate  of  ammonia.  The  presence  of  4  per  cent,  of 
sulphate  of  soda  reduced  the  diffusion  of  carbonate  of  soda  by 
only  ^  of  the  whole.  In  stronger  solutions  the  retardation 
would  probably  be  greater.  There  is,  indeed,  reason  to  be- 
lieve that  the  phenomena  of  liquid  diffusion  are  exhibited  in 
their  simplest  form  only  by  weak  solutions,  the  effect  of 
concentration,  like  that  of  compression  in  gases,  being  to 
produce  a  departure  from  the  normal  character. 

The  rate  of  diffusion  is,  however,  materially  affected  when 
the  liquid  atmosphere  already  contains  a  portion  of  the  dif- 
fusing salt.  The  consideration  of  this  case  leads  to  the 
general  question  of  the  motion  of  particles  of  a  dissolved  sub- 
stance in  a  solution  of  unequal  concentration.  The  general 
law  which  regulates  such  movements  appears  to  be  this :  — 
The  velocity  with  which  a  soluble  salt  diffuses  from  a  stronger 
into  a  weaker  solution^  is  proportional  to  the  difference  of  con- 
centration between  two  contiguou^s  strata.  This  law  has  not  yet 
been  experimentally  demonstrated  in  a  sufficient  number  of 
cases  to  establish  it  completely ;  but  in  the  case  of  chloride 
of  sodium,  it  has  been  shown  to  be  true  by  the  following  ex- 
periments of  Fick.* 

*  Phil.  Mag.  [4],  X.  30. 


DIFFUSION  OF   LIQUIDS.  611 

A  cylindrical  glass  tube,  open  at  both  ends,  was  cemented 
into  a  vessel  completely  filled  with  common  salt,  the  cylin- 
drical space  filled  up  with  water,  and  the  whole  immersed  in 
a  large  jar  containing  water.  The  apparatus  was  then  left  to 
itself  for  several  weeks,  the  water  in  the  jar  being  from  time 
to  time  taken  out  and  renewed.  Now,  as  the  lowest  stratum 
of  liquid  in  the  tube,  being  in  contact  with  undissolved  salt, 
must  remain  constantly  saturated,  while  the  uppermost  layer, 
which  is  in  contact  with  pure  water,  contains  no  salt  at  all, 
a  certain  normal  state  of  diffusion  will  ultimately  establish 
itself  throughout  the  length  of  the  tube,  characterised  by  the 
condition,  that  each  horizontal  stratum  will,  in  a  given  time, 
give  up  to  the  stratum  immediately  above  it  as  much  salt  as 
it  receives  from  the  one  below.  When  this  state  is  attained, 
the  densities  of  the  successive  strata  decrease  from  below 
upwards  in  arithmetical  progression.  This  law  of  decrease 
was  verified  experimentally  by  immersing  in  the  liquid,  at 
various  depths,  a  glass  bulb  suspended  from  the  arm  of  a 
balance,  and  counterpoised  by  weights  in  the  opposite  scale. 
This  law  of  decrease,  however,  is  true  only  with  regard  to 
cylindrical  columns  of  liquid,  or  others,  in  which  the  hori- 
zontal section  is  of  uniform  magnitude.  In  other  cases,  the 
law  of  decrease  of  density  may  be  calculated  according  to  the 
form  of  the  vertical  section.  In  funnel-shaped  tubes,  Fick 
has  shown  that  the  results  of  calculation  agree  with  those  of 
experiment. 

Now  let  K  denote  the  quantity  of  salt  which,  in  the  normal 
state  of  diffusion,  passes  in  a  unit  of  time  through  a  unit  of 
horizontal  section  of  a  cylindrical  tube  whose  height  is  equal 
to  the  unit  of  length:  this  quantity  is  called  the  diffusion- 
coefficient;  also,  let  Q  be  the  quantity  of  salt  which,  in  the 
time  tf  flows  from  the  mouth  of  the  tube  into  the  water-atmo- 
sphere ;  h,  the  height  of  the  tube;  5,  its  horizontal  section;  and 
d,  the  density  of  the  liquid  at  the  bottom ;  then 

Q     =     K,d.  t  t. 
.  h 


612 


DIFFUSION   OF   LIQUIDS. 


FiQ.  44. 


Hence,  with  a  tube  of  given  dimensions,  and  a  solution  of 
known  and  constant  density  at  the  bottom,  the  diffusion- 
coefficient  Ky  of  any  salt,  may  be  calculated  from  the  quantity 
Q,  diffused  out  in  a  given  time. 

This  method  has  been  applied  by  Fick  only  in  the  case  of 
chloride  of  sodium.  It  is,  in  fact,  though  simple  in  principle, 
somewhat  inconvenient  of  application,  on  account  of  the  long 
time — at  least  14  days — which  must  elapse  before  the  normal 
state  is  attained. 

Another  method  of  determining  the  diffusion-coefficient  of 
a  salt  has  been  devised  by  Jolly,  and  applied  in  several  cases 
by  Beilstein.*  The  apparatus  used  consists  of  a  glass  tube 
(Fig.  44),  about  three  inches  long,  bent  round  at  the  bottom, 
and  cut  off  near  the  bend,  so  that  the  level  of  the  orifice  is  not 
much  more  than  a  millimeter  above  the  bottom  of  the  bend  at  a. 
The  upper  end  of  the  tube  is  slightly  drawn  out, 
and  closed  with  a  stopper.  This  tube  is  filled 
with  a  solution  of  known  concentration,  and 
fixed  upright  within  a  jar  of  water,  the  orifice  of 
the  tube  being  2  or  3  lines  below  the  level  of  the 
Avater.  The  salt  then  immediately  begins  to 
diffuse  into  the  water,  and  as  the  liquid  near  the 
orifice  becomes  diluted,  it  passes  round  the  bend 
to  the  upper  part  of  the  tube,  its  place  being 
supplied    by    more    concentrated    liquid    from  ^__ 

above.    With  this  apparatus,  Beilstein  has  ob- 
tained   the    following    diffusion-coefficients   (taking   that    of 
chloride  of  potassium  for  unity),  for  solutions  containing  4  per 
cent,  of  salt,  and  at  the  temperature  of  6°  C.  (10*2°  F.). 

Sulphate  of  potash      .  .  0-6987 

Carbonate  of  soda  .     .  .  0*5436 

Sulphate  of  soda    .     .  .  0-5369 

Sulphate  of  magnesia .  .  0-3587 

Sulphate  of  copper      .  .  0*3440 

Beilstein  infers  from  his  experiments,  that  the  rate  of  dif- 


Chloride  of  potassmm 

.     1 

Nitrate  of  potash    .     . 

.     0-9487 

Chloride  of  sodium     . 

.     0-8337 

Bichi-omate  of  potash . 

.     0-7543 

Carbonate  of  potash    . 

.     0-7371 

*  Ann.  Ch.  Pharm.  xcix.  165. 


DIFFUSION   OF   LIQUIDS.  613 

fusion  is  not  exactly  proportional  to  the  difference  of  density 
of  two  contiguous  strata,  but  increases  in  a  somewhat  greater 
ratio. 

Simmler  and  Wilde  *  are  of  opinion  that  the  want  of  agree- 
ment of  Beilstein's  results  with  this  law  arises  from  a  defect 
in  the  method  of  experimenting.  Beilstein's  calculations, 
indeed,  are  based  on  the  supposition  that  the  strength  of 
the  solution  in  the  tube  (Fig.  44),  though  constantly  de- 
creasing, is  uniform  at  any  instant  of  time  throughout 
the  entire  length;  whereas,  a  little  consideration  will  show 
that  the  density  near  the  orifice  must  be  less  than  that  in 
the  larger  arm  of  the  tube,  and  in  this  arm  less  than  near 
the  bottom  of  the  bend,  where  the  liquid  must  stagnate  to 
a  certain  extent.  From  this  source  of  error,  Fick's  mode  of 
observation  is  free.  Simmler  and  Wilde,  however,  propose 
other  methods,  easier  of  execution  than  Fick's,  and  not  subject 
to  the  necessity  of  waiting  till  the  normal  state  of  diffusion  is 
established.  One  of  these  methods  is  similar  to  that  adopted 
by  Mr.  Graham,  excepting  that  the  vessel  containing  the  solu- 
tion is  perfectly  cylindrical,  a  condition  which  greatly  sim- 
plifies the  calculations ;  and,  instead  of  being  placed  at  the 
bottom  of  the  water-jar,  is  supported  on  a  stand,  so  as  to  bring 
its  mouth  within  a  line  or  two  below  the  surface  of  the  water; 
the  salt,  as  it  diffuses  out,  is  thus  made  to  flow  over  the  sides 
of  the  vessel  and  fall  to  the  bottom,  leaving  an  atmosphere  of 
pure  water  above.  Another  method,  proposed  by  the  same 
authors,  is  to  place  the  saline  solution  in  a  vessel  having  the 
form  of  a  triangular  prism,  and  determine  the  variation  of 
density  at  different  depths  below  the  surface  by  observation  of 
the  indices  of  refraction.  The  numerical  results  obtained  by 
these  methods  have  not  yet  been  published. 

Mixed  salts  may  be  more  or  less  separated  by  their  unequal 
diff'usibility.  A  solution  of  1  part  of  carbonate  of  potash  and 
1  part  of  carbonate  of  soda  in  10  parts  of  water,  yielded  in 

*  Pogg.  Ann.  C.  217. 
VOL.  II.  U  U 


614  DIFFUSION   OF   LIQUIDS. 

19  days  at  60°  F.  a  diffusate  containing  63*6  parts  of  carbonate 
of  potash  to  36*4  parts  of  carbonate  of  soda;  the  diffusate 
obtained  in  25  days  contained  the  two  salts  in  nearly  the 
same  proportion.  Sea-water  was  also  partially  decomposed 
by  diffusion,  the  diffusate  containing  a  smaller  proportion  of 
magnesia-salts  than  the  residue.  The  variation  of  compo- 
sition in  the  water  of  the  Dead  Sea,  at  different  times  of  the 
year,  probably  arises  from  the  unequal  rate  of  diffusion  of 
the  different  salts  contained  in  the  strong  saline  liquid  into 
the  layer  of  fresh  water  brought  down  to  it  during  the  rainy 
season.     (Graham.) 

Diffusion  is  also  capable  of  effecting  the  decomposition  of 
chemical  compounds.  From  a  solution  of  bisulphate  of 
potash,  saturated  at  20°  C.  (68°  F.),  there  were  diffused  in 
50  days,  31*8  parts  of  bisulphate  of  potash,  and  12*8  parts  of 
hydrated  sulphuric  acid.  A  solution  of  8  parts  of  anhydrous 
alum  in  100  parts  of  water  yielded,  in  8  days,  at  17  "9°  C. 
(64*2°  F.),  a  diffusate  of  5*3  parts  alum  and  2-2  parts  sulphate 
of  potash.  A  solution  of  1  part  of  sulphate  of  potash  in 
100  parts  of  lime-water,  left  to  diffuse  into  lime-water  for 
seven  days,  yielded  as  a  mean  result,  a  diffusate  containing 
22*67  parts  of  hydrate  of  potash,  and  77*33  parts  of  sulphate 
of  potash.  A  similar  experiment  with  sulphate  of  soda, 
yielded  a  diffusate  containing  about  12  per  cent,  of  hydrate  of 
soda.  The  larger  quantity  of  the  alkaline  hydrate  obtained 
in  the  first  instance,  appears  to  be  due  to  the  superior  diffusi- 
bility  of  the  sulphate  of  potash,  as  it  can  scarcely  be  supposed 
that  the  affinity  of  potash  for  sulphuric  acid  is  less  than  that 
of  soda.  The  sulphates  of  potash  and  soda  were  also  decom- 
posed by  carbonate  of  lime  dissolved  in  carbonic  acid  water, 
when  the  liquid  was  allowed  to  diffuse  into  pure  water.  The 
chlorides  of  potassium  and  sodium  were  not  sensibly  decom- 
posed by  lime-water  in  this  manner.  When  saturated  solu- 
tions of  lime-water  and  sulphate  of  lime  were  mixed  in  equal 
volumes,  1  per  cent,  of  chloride  of  sodium  dissolved  in  tliQ 


DIFFUSION   OF   LIQUIDS.  615 

mixture,  and  the  solution  left  to  diffuse   into   pure  water, 
scarcely  a  trace  of  hydrate  of  soda  was  obtained ;  but  when 
the  solution  of  sulphate  of  lime,  with  an  addition  of  2  per  cent, 
of  chloride  of  sodium,  was  kept  at  the  boiling  point  for  half 
an  hour,  and  the  solution  mixed  two  or  three  days  afterwards 
with  an  equal  volume  of  lime-water,  and  diffused  into  pure 
water  for  3^  days,  the  diffusate  in  three  cells  was  found  to 
contain  0*234  grains  hydrate  of  soda,  and  0*371  sulphate  of 
soda.     It  appears,  then,  that  more  than  one  condition  of  equi- 
librium is  possible  for  mixed  solutions  of  sulphate  of  lime  and 
chloride  of  sodium.     Cold  solutions  of  these  salts  may  be 
mixed  without  decomposition,  or,  without  sensible  formation 
of  sulphate ;  but,  on  heating,  this  change  is  induced,  and  is 
permanent,  sulphate  of  soda  being  formed,  and  continuing  to 
exist  in  the  cold  solution ;  for  it  is  the  decomposition  of  that 
salt  alone  by  hydrate  of  lime  which  appears  to  yield  the  dif- 
fused hydrate  of  soda.     As  the  effects  of  time  and  tempera- 
ture are  often  convertible,  it  is  possible  that  the  same  decom- 
position might  take  place  at  ordinary  temperatures  after  a 
considerable  time.     "  If  such  be  the  case,  we  have  an  agency 
in  the  soil,  by  which  the  alkaline  carbonates  required  by 
plants  may  be  formed  from  the  chlorides  of  potassium  and 
sodium,   as  well  as  from  the   sulphates,  for  the  sulphate  of 
lime,   generally  present,    will  convert   those   chlorides   into 
sulphates.     The  mode  in  which  the  soil  of  the  earth  is  mois- 
tened by  rain,  is  peculiarly  favourable  to  separations  by  dif- 
fusion.    The  soluble  salts  of  the  soil  may  be  supposed  to  be 
carried  down  together,  to  a  certain  depth,  by  the  first  portion 
of  rain  which  falls,  while  they  find  afterwards  an  atmosphere 
of  nearly  pure  water,  in  the  moisture  which  falls  last  and 
occupies  the  surface-stratum  of  the  soil.     Diffusion  of  the 
salts  upwards  into  the  water,  with  its  separations  and  decom- 
positions, must  necessarily  ensue.     The  salts  of  potash  and 
ammonia,   which  are  most  required  for  vegetation,  possess 
the  highest  diffusibility,  and  will  rise  first.     The  pre-eminent 

u  u  2 


616  OSMOSE. 

diffusibility  of  the  alkaline  hydrates  may  also  be  called  into 
action  in  the  soil  by  hydrate  of  lime,  particularly  as  quick- 
lime is  applied  for  a  top-dressing  to  grass  lands."  (Graham.*) 


PASSAGE   OF   LIQUIDS   THROUGH  POROUS   SEPTA.      OSMOSE. 

The  force  of  liquid  diffusibility  still  acts  when  the  two 
liquids  are  separated  by  a  porous  sheet  of  animal  membrane, 
or  unglazed  earthenware ;  for  the  pores  of  such  a  membrane 
are  occupied  by  water,  and  an  uninterrupted  liquid  commu- 
nication exists  between  the  water  on  the  one  side,  and  the 
saline  solution  on  the  other.  Under  these  circumstances,  a 
flow  of  liquid  takes  place,  generally,  though  not  always,  from 
the  water  to  the  saline  solution,  so  that  the  quantity  of  liquid 
diminishes  on  one  side  of  the  septum,  while  it  increases  on 
the  other.  This  phenomenon  was  originally  designated  by 
the  correlative  terms,  Endosmose  and  Exosmose ;  but  it  is 
better  expressed  b}'-  the  shorter  word  Osmose  (from  cja-fio9, 
impulsion),  which  includes  the  two  former. 

This  passage  of  liquids  through  porous  septa,  was  first 
studied  by  Dutrochet,  whose  apparatus,  called  an  endosmometer, 
consisted  of  a  narrow  glass  tube,  having  a  funnel-shaped 
expansion  at  the  bottom,  and  closed  at  that  end  by  a  piece 
of  bladder.  This  tube  was  filled  with  a  saline  solution,  and 
placed  in  a  vertical  position,  in  a  jar  containing  water.  The 
flow  of  liquid  in  one  direction  or  the  other,  was  measured  by 
the  rise  or  fall  of  the  liquid  in  the  tube.  Dutrochet  inferred 
from  his  experiments  that  the  velocity  of  the  osmotic  current 
is  proportional  to  the  quantity  of  salt  or  other  solid  substance 
originally  contained  in  the  saline  solution.  The  experiments 
were,  however,  inexact,  because  no  allowance  was  made  for 
the  alteration  of  hydrostatic  pressure,  caused  by  the  rise  or 
fall  of  liquid  in  the  tube.  Vierordt  f ,  who  used  a  modification 
of  Dutrochet's  apparatus,  in  which  this  source  of  error  was 

♦  Chem.  Soc.  Qu.  J.  iii.  67,  f  Pogg.  Ann.  Ixxiii.  519. 


OSMOSE.  617 

removed,  found  that  the  velocity  of  the  current  increases  with 
the  initial  concentration  of  the  solution,  but  in  a  lower  ratio. 

Professor  Jolly  of  Heidelberg,  has  examined  the  osmose  of 
water  and  saline  solutions  by  a  different  method.  The  saline 
solution  containing  a  known  quantity  of  salt,  is  contained  in  a 
glass  tube  closed  at  the  bottom  with  bladder,  and  plunged  into 
water,  which  is  frequently  changed,  so  as  to  keep  it  nearly  pure. 
The  tube  with  its  contents  is  taken  out  from  time  to  time 
and  weighed,  and  these  operations  are  repeated  till  the  weight 
becomes  constant,  showing  that  the  whole  of  the  salt  has  passed 
out  from  the  tube,  and  nothing  but  water  remains. 

In  this  manner,  it  is  found  that  a  given  quantity  of  any 
salt  which  passes  through  the  septum  into  the  water  is  always 
replaced  by  a  definite  quantity  of  water.  The  quantity  of 
water  which  is  thus  replaced  by  a  unit  of  weight  of  the  salt,  is 
called  the  endosmotic  (or  osmotic)  equivalent  of  that  salt.  This 
quantity  varies  with  the  nature  of  the  salt,  and  with  the 
temperature,  increasing  as  the  temperature  rises,  but  it  is 
independent  of  the  density  of  the  solution.  At  temperatures 
near  0°  C,  the  endosmotic  equivalent  of  hydrate  of  potash  was 
found  to  be  200 ;  of  chloride  of  sodium,  between  4*3  and  4*6; 
of  sulphate  of  soda,  between  11  and  12;  of  neutral  sulphate 
of  potash,  12 ;  of  acid  sulphate  of  potash,  2 '3 ;  and  of  hy- 
drated  sulphuric  acid  (at  18°  C),  0*35. 

These  results  point  to  the  conclusion,  that  the  osmose 
between  water  and  saline  solutions,  consists,  not  in  the  opposite 
passage  of  two  liquid  currents,  but  in  the  passage  of  particles 
of  the  salt  in  one  direction,  and  of  pure  water  in  the  other. 
This  conclusion  is  strengthened  by  Mr.  Graham's  observation, 
that  common  salt  diffuses  into  water,  through  a  thin  membrane 
of  ox-bladder  deprived  of  its  outer  muscular  coating,  at  the 
same  rate  as  when  no  membrane  is  interposed. 

The  flow  of  water  into  the  saline  solution  is  the  only  one 
of  the  two  movements  which  can  be  correctly  described  as  a 
current.     This  is,  in  fact,  the  true  osmose,  and  depends  es- 

U  u  3 


618  OSMOSE. 

Bentiallj  on  the  action  of  the  membrane  or  other  porous  septum ; 
for  the  quantity  of  water  which  thus  passes  into  the  solution, 
is  often  much  greater  than  would  be  introduced  by  mere 
liquid  diffusion,  amounting  in  some  cases  to  several  hundred 
times  that  of  the  salt  displaced. 

This  action  of  the  septum  has  been  explained  in  various 
ways.  By  Datrochet  and  others,  it  was  attributed  to  capil- 
larity ;  but  this  force  is  quite  insufficient  to  account  for  the 
great  inequality  of  ascension  which  different  liquids  exhibit 
in  the  osmotic  apparatus ;  in  fact,  Mr.  Graham  has  shown, 
that  solutions  of  the  most  different  character  exhibit  very 
nearly  equal  ascension  in  tubes  of  equal  diameter. 

Osmose  has  likewise  been  attributed  to  the  unequal  absorp- 
tion of  the  two  liquids  by  the  porous  septum.  Suppose 
the  septum  to  be  of  such  a  nature  as  to  absorb  only  one 
of  the  liquids,  the  water  for  instance.  The  water  will 
then  penetrate  the  septum,  and  coming  in  contact  with  the 
saline  solution,  will  diffuse  into  it.  More  water  will  then 
be  absorbed,  and  subsequently  diffused,  and  thus  a  continuous 
current  will  be  set  up.  If  both  liquids  are  absorbed  by  the 
septum,  but  in  different  degrees,  and  each  is  capable  of  dif- 
fusing into  the  other,  like  water  and  alcohol,  the  result  will 
be  the  formation  of  two  unequal  currents  in  opposite  direc- 
tions. Water  is  absorbed  by  animal  membrane  much  more 
rapidly  than  most  other  liquids,  and  accordingly,  when  a 
septum  of  this  kind  is  used,  the  direction  of  the  current  is  in 
most  cases  from  the  water  to  the  other  liquid.  According  to 
Liebig,  a  given  weight  of  dried  ox-bladder  absorbs  in  the  same 
time,  200  volumes  of  water,  133  vols,  of  a  saturated  solution 
of  common  salt,  38  vols,  of  alcohol  of  the  strength  of  84  per 
cent.,  and  17  vols,  of  bone-oil.  When  water  and  alcohol  are 
separated  by  an  animal  membrane,  the  quantity  of  water 
which  passes  into  the  alcohol,  is  greater  than  the  quantity  of 
alcohol  which  passes  into  the  water;  but  when  the  same  liquids 
are  divided  by  a  thin  film  of  collodion,  which  absorbs  alcohol 
more  quickly  than  water,  the  contrary  effect  is  produced. 


OSMOSE.  619 

On  the  other  hand,  the  numerous  experiments  recently 
made  by  Mr.  Graham  *,  lead  to  the  conclusion,  that  osmose 
depends  essentially  on  the  chemical  action  of  the  liquid  on  the 
septum.  These  experiments  were  made  partly  with  porous 
mineral  septa,  partly  with  animal  membrane.  The  earthen- 
ware osmometer  consisted  of  the  porous  cylinders  employed 
in  voltaic  batteries,  about  five  inches  in  depth,  surmounted  by 
a  glass  tube  0*6  inch  in  diameter,  attached  to  the  mouth  of 
the  cylinder  by  means  of  a  cap  of  gutta  percha.  The  cylinder 
was  filled  to  the  base  of  the  glass  tube  with  a  saline  solution, 
and  immediately  placed  in  a  jar  of  distilled  water ;  and  as  the 
fluid  within  the  instrument  rose  during  the  experiment,  water 
was  added  to  the  jar  to  equalise  the  pressure.  The  rise  (or 
fall)  of  the  liquid  in  the  tube  was  very  regular,  as  observed 
from  hour  to  hour,  and  the  experiment  was  generally  termi- 
nated in  five  hours.  From  experiments  made  on  solutions  of 
every  variety  of  soluble  substance,  it  appeared  that  the  rise 
or  osmose,  is  quite  insignificant  with  neutral  organic  sub- 
stances in  general,  such  as  sugar,  alcohol,  urea,  tannin,  &c. ; 
so  likewise  with  neutral  salts  of  the  earths  and  ordinary 
metals,  with  the  chlorides  and  nitrates  of  potassium  and 
sodium,  and  with  chloride  of  mercury.  A  more  sensible  but 
still  very  moderate  osmose  is  exhibited  by  hydrochloric,  nitric, 
acetic,  sulphurous,  citric,  and  tartaric  acids.  These  are  sur- 
passed by  the  stronger  mineral  acids,  such  as  sulphuric  and 
phosphoric,  and  by  sulphate  of  potash,  which  are  again  ex- 
ceeded by  salts  of  potash  and  soda  possessing  a  decided  acid 
or  alkaline  reaction,  such  as  binoxalate  of  potash,  phosphate 
of  soda,  or  the  carbonates  of  potash  and  soda.  The  highly 
osmotic  substances  were  also  found  to  act  with  most  advantage 
in  small  proportions,  producing,  in  fact,  the  largest  osmose  in  the 
proportion  of  one-quarter  percent,  dissolved.  (See  page  621.) 
The  same  substances  are  likewise  always  chemically  active 
bodies,  and  possess  afiinities  which  enable  them  to  act  on  the 

*  Phil.  Trans.  1855,  177  ;  Chem.  Soc.  Qu.  J.  viii.  43. 
u  u  4 


620 


OSMOSE. 


Fig.  45. 


material  of  the  earthenware  septum.  Lime  and  alumina  were 
always  found  in  solution  after  osmose,  and  the  corrosion 
of  the  septum  appeared  to  be  a  necessary  condition  of  the  flow. 
Septa  of  other  materials,  such  as  pure  carbonate  of  lime,  gyp- 
sum, compressed  charcoal,  and  tanned  sole-leather,  although 
not  deficient  in  porosity,  gave  no  osmose,  apparently  because 
they  are  not  chemically  acted  on  by  the  saline  solutions. 

Similar  results  were  obtained  with  septa  of  animal  mem- 
brane. Ox- bladder  was  found  to  act  with  much  greater 
strength  and  regularity  when  divested  of  its  outer  muscular 
coat.  Cotton-calico,  impregnated  with  liquid  albumen,  and 
afterwards  heated  to  coagulate  the  albumen,  formed  an  excel- 
lent septum,  resembling  membrane  in  every  respect.     The 

osmometer  (Fig.  45)  used 
in  these  experiments  was 
arranged  like  the  original 
instrument  of  Dutrochet ; 
but  the  membrane  was  sup- 
ported by  a  plate  of  per- 
forated zinc,  and  the  tube 
was  of  considerable  diame- 
ter, viz.  one-tenth  of  that 
of  the  mouth  of  the  bulb, 
or  of  the  disc  of  membrane 
exposed  to  the  liquids. 

Osmose  in  membrane 
presents  many  points  of 
similarity  to  that  in  earth- 
enware. The  membrane 
is  constantly  undergoing 
decomposition,  and  its  os- 
motic action  is  exhaustible. 
Salts  and  other  substances 
capable  of  determining  a 
large  osmose,  are  all  clie- 


OSMOSE.  621 

mically  active  substances,  while  the  great  mass  of  neutral 
organic  substances  and  perfectly  neutral  monobasic  salts  of 
the  metals,  such  as  chloride  of  sodium,  possess  only  a  low 
degree  of  action,  or  are  wholly  inert.  The  active  substances 
are  also  most  efficient  in  small  proportions.*  With  a  solution 
containing  -^  per  cent,  of  carbonate  of  potash,  the  rise  in  the 
osmometer  was  167  millimeters;  and  with  1  per  cent,  of  the 
same  salts,  206  millimeters  in  five  hours.  With  another 
membrane  and  a  stronger  solution,  the  rise  was  863  millime- 
ters, or  upwards  of  38  inches,  in  the  same  time.  To  induce 
osmose,  the  chemical  action  on  the  membrane  must  be  diffe- 
rent on  the  two  sides,  and  apparently  not  in  degree  only,  but 
in  kind,  viz.  an  alkaline  action  on  the  albuminous  substance 
of  the  membrane  on  the  one  side,  and  an  acid  action  on  the 
other.  The  water  appears  always  to  accumulate  on  the 
alkaline  or  basic  side  of  the  membrane.  Hence,  with  an 
alkaline  salt,  such  as  carbonate  of  soda,  in  the  osmometer, 
and  water  outside,  the  flow  is  inwards ;  but  with  an  acid  in 
the  osmometer,  there  is  negative  osmose,  or  the  flow  is  in- 
wards, the  liquid  then  falling  in  the  tube.  The  chlorides  of 
barium,  sodium,  and  magnesium,  and  similar  neutral  salts, 
are  wholly  indifferent,  or  appear  to  act  merely  in  a  subor- 
dinate manner  to  some  other  active  acid  or  basic  substance, 
which  may  be  present  in  the  solution  or  the  membrane  in  the 
most  minute  quantity.  Salts  which  admit  of  division  into  a 
basic  salt  and  free  acid,  exhibit  an  osmotic  activity  of  the 
highest  order,  e.  g,  the  acetate  and  various  other  salts  of 
alumina,  ferric  oxide  and  chromic  oxide,  dichloride  of  copper, 
proto-chloride  of  tin,  nitrate  of  lead,  &c.  The  acid  travels 
outwards  by  difi'usion,  superinducing  a  basic  condition  of  the 
inner  surface  of  the  membrane,  and  an  acid  condition  of  the 


*  The  action  increases  with  the  strength  of  the  solution  up  to  a  certain 
point,  as  the  above  examples  show  (see  also  p.  619).  With  stronger  solutions 
the  pores  of  the  membrane  probably  become  stopped  up  with  particles  of  salt, 
and  the  action  consequently  diminishes. 


622 


OSMOSE. 


outer  surface,  the  most  favourable  condition  for  a  liigh  posi- 
tive osmose.  Again,  the  bibasic  salts  of  potash  and  soda, 
such  as  the  sulphate  and  tartrate,  though  strictly  neutral  in 
properties,  begin  to  exhibit  a  positive  osmose,  in  consequence, 
perhaps,  of  their  resolution  into  an  acid  supersalt  and  free 
alkaline  base. 

The  following  table  exhibits  the  osmose  of  substances  of 
all  classes  through  membrane,  the  degree  being  a  rise  or  fall 
of  one  millimeter  :  — 


Osmose  op  1  per  Cent.  Solutions  in  Membrane. 


Degrees. 

Degrees 

Oxalic  acid  . 

.      -148 

Chloride  of  zinc  . 

.      +64 

Hydrochloric  acid  (0 

1  per 

Chloride  of  nickel 

88 

cent.) 

.     -  92 

Nitrate  of  lead     . 

.    125  to  211 

Terchloride  of  gold 

.     -  54 

Nitrate  of  cadmium 

.       137 

Bichloride  of  tin  . 

.     -  46 

Nitrate  of  uranium 

.    234  to  458 

Bichloride  of  platinum 

.     -   30 

Nitrate  of  copper 

.       204 

Chloride  of  magnesium 

.     -     3 

Chloride  of  copper 

.       351 

Chloride  of  sodium 

.      +      2 

Protochloride  of  tin 

.       289 

Chloride  of  potassium 

18 

Protochloride  of  iron 

.       435 

Nitrate  of  soda    . 

2 

Chloride  of  mercury 

121 

Nitrate  of  silver  . 

34 

Mercurous  nitrate 

.       356 

Sulphate  of  potash 

21  to  60 

Mercuric  nitrate  . 

.       476 

Sulphate  of  magnesia 

14 

Ferric  acetate 

.       194 

Chloride  of  calcium 

20 

Acetate  of  alumina 

280  to  393 

Chloride  of  barium 

21 

Chloride  of  aluminium 

.       540 

Chloride  of  strontium 

26 

Phosphate  of  soda 

.       311 

Chloride  of  cobalt 

26 

Carbonate  of  potash     . 

.       439 

Chloride  of  manganese 

34 

The  osmotic  action  of  carbonate  of  potash  and  other  alka- 
line salts  is  interfered  with  in  an  extraordinary  manner  by 
the  presence  of  chloride  of  sodium,  being  reduced  to  almost 
nothing  by  an  equal  proportion  of  that  salt.  The  moderate 
positive  osmose  of  sulphate  of  potash  is  converted  into  a  very 
sensible  negative  osmose  by  the  presence  of  the  merest  trace 
of  a  strong  acid,  while  the  positive  osmose  of  the  same  salt 
is  singularly  promoted  by  a  small  proportion  of  alkaline  car- 
bonate :  thus  a  1  per  cent,  solution  of  sulphate  of  potash  gives 
an  osmose  of  21  degrees,  but  the  addition  of  0-1  per  cent,  of 


OSMOSE.  623 

carbonate  of  potash  raises  it  to  between  254  and  264  degrees. 
(Graham.) 

If  a  glass  tube,  bent  in  the  form  of  a  siphon,  and  having 
its  shorter  leg  closed  with  bladder,  be  partially  filled  with 
salt-water,  the  shorter  leg  then  immersed  in  a  vessel  of  pure 
water,  and  mercury  poured  into  the  longer  leg,  so  that  its 
pressure  may  act  in  opposition  to  the  force  with  which  the 
water  tends  to  enter  the  saline  solution  through  the  bladder, 
it  will  be  found  that,  when  the  column  of  mercury  attains  a 
certain  height,  the  two  liquids  will  mix  without  change  of 
volume,  the  force  of  the  osmotic  current  being  then  exactly 
balanced  by  the  weight  of  the  mercurial  column.  In  this 
way  the  mechanical  force  of  the  osmotic  current  may  be 
measured.     (Liebig.) 

Osmose  appears  to  play  an  important  part  in  the  functions 
of  life.  We  have  seen  that  it  is  peculiarly  excited  by  dilute 
saline  solutions,  such  as  the  animal  and  vegetable  juices  are, 
and  that  the  acid  or  alkaline  property  which  these  juices 
possess  is  another  favourable  condition  for  their  action  on 
membrane.  The  natural  excitation  of  osmose  in  the  sub- 
stance of  the  membranes  or  cell-walls  dividing  such  solutions 
seems  therefore  almost  inevitable. 

In  osmose  there  is  also  a  remarkably  direct  substitution  of 
one  of  the  great  forces  of  nature  by  its  equivalent  in  another 
force,  the  conversion,  namely,  of  chemical  action  into  mechani- 
cal power.  Viewed  in  this  light,  the  osmotic  injection  of 
fluids  may,  perhaps,  supply  the  deficient  link  which  inter- 
venes between  chemical  decomposition  and  muscular  move- 
ment. The  ascent  of  the  sap  in  plants  appears  to  depend 
upon  a  similar  conversion  of  chemical,  or,  at  least,  molecular 
action  into  mechanical  force.  The  juices  of  plants  are  con- 
stantly permeating  the  coatings  of  the  superficial  vessels  in 
the  leaves  and  other  organs ;  and  these  evaporating  into  the 
air,  a  fresh  portion  of  liquid  is  then  absorbed  by  the  mem- 
brane and  evaporates ;  and  thus  a  regular  upward  current 


624  DIFFUSION   OF   GASES. 

is  established,  hy  which  the  sap  is  transferred  from  the  roots 
to  the  highest  parts  of  the  tree.  In  a  similar  manner,  the 
evaporation  constantly  taking  place  from  the  skin  and  lungs 
of  animals,  causes  a  continuous  flow  of  the  animal  juices  from 
the  interior  towards  the  surface. 


DIFFUSION   OF   GASES   THKOUGH   POKOUS   SEPTA. 

It  appears  from  Mr.  Graham's  experiments  (I.  87),  that  the 
rates  of  diffusion  of  gases  through  porous  diaphragms,  such 
as  dry  gypsum,  cork,  unglazed  earthenware,  or  bladder,  are 
to  one  another  in  the  inverse  ratio  of  the  squares  of  their 
densities,  the  law  being,  in  fact,  the  same  as  that  of  the 
effiLsion  of  the  same  gases  into  a  vacuum  through  minute 
apertures  in  a  metal  plate  (I.  78).  Bunsen  has  arrived  at  a 
different  conclusion.*  He  finds,  for  example,  that  when  a 
tube  containing  hydrogen  is  closed  by  a  dry  gypsum  diaphragm, 
and  a  current  of  oxygen  passed  rapidly  over  the  diaphragm, 
so  that  the  hydrogen  may  diffuse  into  an  infinite  atmosphere  of 
oxygen,  the  volume  of  oxygen  which  enters  the  tube  is  to  the 
volume  of  hydrogen  which  issues  from  the  tube,  as  1  :  3*345, 
this  ratio  remaining  constant  during  the  whole  time  of  the 
diffusion.  The  law  of  the  inverse  square  roots  of  the  densities 
would  give  1  :  4.  Again,  when  oxygen  was  made  to  pass 
through  stucco  into  oxygen,  and  hydrogen  into  hydrogen, 
by  difference  of  pressure,  it  was  found  that,  under  the  same 
pressure,  the  rate  of  issue  of  the  oxygen  was  to  that  of 
the  hydrogen  as  1  :  2-73  instead  of  1  :  4.  These  differences 
are  too  great  to  be  accounted  for  by  error  of  observation ; 
they  probably  arise  from  the  circumstance,  that  Graham's 
experiments  were  made  with  thin  diaphragms,  whereas 
Bunsen  used  diaphragms  of  considerable  thickness  f,  in  which 
case,  the  rates  of  diffusion  would  approximate  to  the  rates  of 

♦  See  Bunsen's  "  Gasometry,"  translated  by  Dr.  Roscoe,  pp.  198 — 233. 
t  Compare  the  figure  at  page  87,  Vol.  1,  of  this  work,  with  figure  53, 
p.  202.  of  Bunsen's  "Gasometry." 


HEAT   PROM   CHEMICAL   ACTION.  625 

transpiration  (I.  82.)  rather  than  to  those  of  effusion.  The 
rate  of  transpiration  through  a  mass  of  porous  stucco  was 
ascertained  by  Mr.  Graham  to  be  the  same  as  through 
capillary  tubes,  namely,  1  volume  of  oxygen  to  2*3  volumes 
of  hydrogen.  In  the  interior  of  a  considerable  mass  of  stucco, 
with  hydrogen  on  one  side  and  oxygen  on  the  other,  the  stucco 
acts  as  a  vessel,  a  partial  vacuum  being  formed  in  its  centre. 
To  this  point,  both  oxygen  and  hydrogen  are  impelled  by 
pressure  (transpiration)  in  the  ratio  of  1  to  2*3,  instead  of  1  to 
4,  the  relation  of  diifusion.  Hence  the  oxygen  travels  through 
the  diaphragm,  partly  in  one  of  these  ratios  and  partly  in  the 
other,  and  the  proportion  of  oxygen  which  enters  the  vessel 
is  increased,  as  in  Bunsen's  experiments.* 


DEVELOPMENT    OF   HEAT   BY   CHEMICAL 
ACTION. 

From  the  time  when  Lavoisier  pointed  out  the  true  nature 
of  the  phenomenon  of  combustion,  the  measurement  of  the  heat 
evolved  in  chemical  combination  has  occupied  a  prominent 
place  in  the  attention  of  chemists,  and  has  been  made  the 
subject  of  numerous  researches,  the  most  exact  and  compre- 
hensive of  which,  are  those  of  Messrs.  Favre  and  Silbermann, 
and  of  Dr.  Andrews,  f 

The  apparatus  used  by  Favre  and  Silbermann  for  measur- 
ing the  heat  evolved  by  the  combustion  of  various  substances 
in  oxygen  gas,  is  represented,  with  the  omission  of  minor  details, 
in  figure  46.  C  is  a  vessel  of  gilt  brass  plate,  immersed  in 
a  water-calorimeter,  A  A,  of  silvered  copper-plate,  and  the 
latter  is  enclosed  in  an  outer  vessel,  BB,  the  space  between 
A  and  B  being  filled  with  swan-down,  to  prevent  the  escape 
of  heat  from  the  water  in  A,     The  vessels  A  and  B  are  closed 

♦  Ann.  Ch.  Phys.  [3],  xxxiv.  357  ;  xxxvi.  5;  xxxvii.  405  ;  Abstr.  Chcm. 
Soc.  Qu.  J.  vi.  234. 

t  Phil.  Mag.  [3],  xxxii.  321,  392,  and  426. 


626 


HEAT   FROM   CHEMICAL   ACTION. 


Fig.  46. 


with  lids  having   apertures  for   the  insertion  of  tubes  and 
thermometers.     The  combustions  are  performed  in  the  vessel 

C,  into  which  oxygen  gas  is  in- 
troduced through  the  tube  c  d,  and 
the  gaseous  products  of  the  com- 
bustion escape  by  the  tube  efg  h, 
the  lower  part  of  which  is  bent 
into  numerous  coils,  to  facilitate 
as  much  as  possible,  the  transmis- 
sion of  the  heat  of  these  gases 
to  the  water  in  the  calorimeter. 
The  extremity  A,  of  this  tube  is 
connected  with  a  gasometer,  or 
with  an  absorbing  apparatus.  To 
ensure  uniformity  of  temperature 
in  the  water,  a  flat  ring  of  metal 
i  i,  is  moved  up  and  down  by 
means  of  the  rod  K  i.  Combustible 
gases  were  introduced  into  the  vessel  C,  by  means  of  fine 
tubes,  the  gas  being  previously  set  on  fire  at  the  aperture. 
Solid  bodies  were  attached  to  fine  platinum  wires  suspended 
from  the  lid  of  the  calorimeter  :  liquids  were  burned  in  small 
capsules  or  in  lamps  with  asbestos  wicks ;  charcoal  was  dis- 
posed in  a  layer  on  a  sieve-formed  bottom,  through  the  open- 
ings of  which  the  oxygen  had  access  to  it.  The  heat  evolved 
was  measured  by  the  rise  of  temperature  of  the  known  quan- 
tity of  water  in  the  calorimeter. 

For  processes  which  take  place  without  access  or  escape  of 
gases,  simpler  apparatus  may  be  used.  For  such  reactions  Favre 
and  Silbermann  employed  a  mercury-calorimeter,  (Fig.  47), 
jijQ  47  consisting    of   a   glass 

globe  filled  with  mer- 
cury, and  having  in- 
serted into  it  a  tube  a,  to 
contain  the  combining 


HEAT   FROM   CHEMICAL   ACTION. 


627 


substances,  an  acid  and  a  base  for  instance.  The  mercury  in 
the  globe  communicates  by  the  bent  tube  h,  with  the  capil- 
lary tube  c  d,  on  which  its  expansion  is  measured.  The 
apparatus  forms,  in  fact,  a  large  mercurial  thermometer. 

The  unit  of  weight  to  which  the  following  numbers  refer 
is  the  gramme,  and  the  unit  of  heat  is  the  quantity  required 
to  raise  the  temperature  of  1  gramme  of  water  from  0°  to  1°  C. 


Substance. 


Gases. 
Hydrogen  .    . 
Carbonic  oxide 
Marsh-gas  .    . 
Olefiant-gas    . 

Liquids. 


Amylene    .    . 
Oil  of  turpentine 


Ether 


Wood- spirit  .  , 
Alcohol.  .  .  . 
Amylic  alcohol    . 

Acetic  acid     .     . 
Butyric  acid    .     . 
Valerianic  acid    . 
Palmitic  acid  (solid) 
Stearic  acid  (solid) 

Formiate  of  methyl 
Acetate  of  methyl 
Formiate  of  ethyl 
Acetate  of  ethyl  . 
Butyrate  of  methyl 
Butyrate  of  ethyl 
Valerate  of  methyl 
Spermaceti  (solid) 

Sulphide  of  carbon 


Formula. 


HH 

GO 
GH, 


GH,0 
GoH«0 


^2  "4^2 

G5"i0^2 
^16"  32^2 

T72  ri  4TT2 

G3n,o, 

G,HA 

G,H.,0, 
GgHjjOj 

^32"^6  4^2 


Products. 


H2O 


GO2  and  SOi 


Heat  of  Combustion. 


1  Grm.  of 
Substance 

with 
Oxygen. 


r 34462 
133802 
f  2403 
1  2431 
r 13063 
\  13168 
f  11858 
(_  11942 


11491 
10852 

9028 

5307 
7184 
8959 

3505 
5647 
6439 
9316 
9716 

4197 
5342 
5279 
6293 
6791 
7091 
7376 
10342 

3401 


1  Grm.  of 

Oxygen 

with 

Substance, 


4308 
4226 
4205 
4255 
3266 
3277 
3458 
3483 


3352 
3294 

3479 

3538 
3442 
3285 

3286 
3106 
3158 
3240 
3317 

3935 
3529 
3488 
3461 
3334 
3213 
3342 
3301 

2692 


Observers. 


F.S. 

A. 
F.S. 

A. 

F.S. 

A. 
F.S. 

A. 


F.S. 


628 


HEAT   FROM   CHEMICAL   ACTION. 


Substance. 


Formula. 


Products. 


Heat  of  Combustion. 


1  Grm.  of 
Substance 

with 
Oxygen. 


1  Grm.  of 

Oxygen 

with 

Substance, 


Solids. 

Carbon    (wood-char-   1 

coal) J 

Sulphur  (rhombic)   .     . 
Phosphorus  (yellow)     . 

Zinc 

Iron 

Tin 

Protoxide  of  tin  .     .     . 

Copper 

Red  oxide  of  copper  . 


PP 
ZnZn 

FeFe 

SnSn 
Sn^O 
CuCu 
Cu,0 


Zn^O 

SnO 
SnO 
Cu,0 


2473 

8080 

2221 

5953 

1301 

1575 

1167 

521 

604 

256 


1855 
3030 
2221 
4613 
5366 
4134 
4230 
4349 
2394 
2288 


F.S. 


A  comparison  of  the  numbers  in  this  Table,  shows  that  the 
quantities  of  heat  evolved  by  the  combination  of  a  constant 
weight  of  oxygen  with  different  combustible  bodies,  are  much 
more  nearly  equal  than  the  quantities  evolved  by  the  com- 
bustion of  equal  weights  of  these  several  bodies.  Neverthe- 
less, the  conclusion  drawn  from  older  experiments  (I.  300), 
that  the  quantity  of  heat  evolved  in  combustion  is  always 
proportionate  to  the  quantity  of  oxygen  consumed,  is  very  far 
from  being  confirmed  by  the  numbers  in  the  fifth  column  of 
the  preceding  Table. 

Equal  weights  of  isomeric  bodies  do  not  evolve  equal 
quantities  of  heat  in  combustion.  This  may  be  seen  by 
comparing  the  numbers  for  formiate  of  ethyl  and  acetate  of 
methyl,  for  acetic  acid  and  formiate  of  methyl,  &c. 

In  homologous  organic  compounds,  the  heat  of  combustion 
for  equal  weights  of  the  compounds  increases,  as  the  carbon 
and  hydrogen  bear  a  greater  proportion  to  the  oxygen.  This 
may  be  seen  in  the  series  of  alcohols,  fatty  acids,  and  com- 
pound ethers. 

In  general,  the  heat  evolved  by  the  combustion  of  an  oxi- 
dised body,  such  as  carbonic  oxide,  or  protoxide  of  tin,  is  less 


HEAT   OIT    CHEMICAL    COMBINATION.  629 

than  that  which  is  evolved  in  the  complete  oxidation  of  the 
combustible  constituent. 

But  little  is  known  respecting  the  relation  which  the  heat 
of  combustion  of  a  compound  of  two  or  more  combustible 
substances  bears  to  the  sum  of  the  heats  of  combustion  of  its 
constituents.  In  some  cases,  it  is  less  than  that  sum  {e.  g. 
marsh-gas  and  defiant  gas);  in  others,  greater  (bisulphide  of 
carbon,  oil  of  turpentine).  The  relation  in  question  is, 
doubtless,  greatly  affected  bj  the  molecular  states  of  the 
compound  and  of  its  elements  in  the  separate  state.  That 
the  heat  of  combustion  of  a  body  is  materially  influenced 
by  its  state  of  aggregation,  is  shown  by  many  experiments ; 
and  in  general  it  is  found  that,  of  two  modifications  of  a  sub- 
stance, that  which  has  the  greater  specific  heat,  likewise 
evolves  the  greater  quantity  of  heat  in  combination.  Thus, 
the  specific  heat  of  yellow  phosphorus  is  greater  than  that  of 
the  red  variety ;  now  1  gramme  of  yellow  phosphorus,  in 
burning  to  phosphoric  acid,  evolves  5953  heat-units,  whereas 
the  same  quantity  of  red  phosphorus  evolves  only  5070  heat- 
units.  The  same  relation  is  strikingly  shown  by  the  fol- 
lowing comparison  of  the  quantities  of  heat  evolved  in  the 
complete  combustion  of  equal  weights  of  different  kinds  of 
carbon,  as  determined  by  Favre  and  Silbermann,  with  their 
specific  heats,  as  determined  by  Regnault :  — 


Heat  of 
Combustion. 

Specific 
Heat. 

Wood-charcoal 

.     8080     . 

0-24150 

Coke  from  gas-retorts 

.     8047     . 

0-20360 

Native  graphite 

.     7797     . 

0-20187 

Graphite  from  blast-furnaces 

.     7762     .     , 

0-19702 

Diamond 

.     7770     . 

0-11687 

Sulphur  likewise  evolves  in  combustion  different  quantities 
of  heat,  according  to  its  state  of  aggregation.  Octohedral 
sulphur,  native  or  artificial,  gives,  as  a  mean  result,  2221  heat- 

VOL.  II.  X  X 


630 


HEAT   OF   CHEMICAL   COMBINATION. 


units;  prismatic  sulphur,  recently  crystallised  from  fusion, 
gives  2260  heat -units. 

Combination  of  Metals  with  Chloriney  Bromine,  and  Iodine, 
— To  determine  the  heat  evolved  in  the  combination  of  metals 
with  chlorine,  Andrews  introduced  the  metals,  enclosed  in 
thin  glass  bulbs,  into  a  glass  vessel  filled  with  dry  chlorine. 
This  vessel  was  placed  within  the  water-calorimeter,  and  the 
glass  bulb  broken  by  shaking  the  vessel.  The  results  are 
given  in  the  following  Table.  The  number  for  hydrogen  is 
from  the  experiments  of  Favre  and  Silbermann:  — 


Substance. 

Product. 

Heat  of  Combustion. 

1  Gramme  of  Substance 

1  Gramme  of  Chlorine 

* 

with  Clilorine. 

with  Substance. 

Hydrogen     . 

HCl 

23783 

670 

Potassium     . 

KCl 

2655 

2932 

Zinc 

ZnCl 

1529 

1404 

Copper    .... 

CnCl 

961 

858 

Iron ..... 

Fe^Cla 

1745 

317 

Tin 

SnCl, 

1079 

881 

Arsenic  .... 

ASCI3 

994 

700 

Antimony     . 

SbClg 

707 

799 

If  we  multiply  the  numbers  which  express  the  heat  of 
combination  of  1  gramme  of  each  of  the  metals  with  oxygen 
and  chlorine,  by  the  atomic  weights  of  the  several  metals,  we 
obtain  the  following  numbers  for  the  quantities  of  heat 
evolved  by  equivalent  quantities  of  these  metals  in  combining 
with  oxygen  and  chlorine :  — 


With  8  gr.  Oxygen. 

1  gramme  of  hydrogen      ....  34462 

32-6         „         zinc 42413 

31-7         „        copper I9147 

29  „        tin  (to  SnO  and  SnCL)         ,  33843 


With  35-5  gr.Cl. 
23783 
49844 
30464 
31291 


The  numbers  in  this  Table  do  not  exhibit  any  simple  rela- 
tion to  each  other,  so  that  no  conclusion  can  be  drawn  from 
them  as  to  the  quantity  of  heat  evolved  or  absorbed  in  the 


HEAT   OF    CHEMICAL   COMBINATION. 


631 


substitution  of  chlorine  for  oxygen,  or  of  one  metal  for 
another  in  combination  with  either  of  these  elements.  Here, 
as  in  other  cases,  the  difference  in  the  state  of  aggregation 
doubtless  interferes  with  the  constancy  of  action  which  might 
otherwise  be  observed.  The  amount  of  interference  arising 
from  this  cause  is  much  diminished  when  compounds  are 
compared  in  the  state  of  aqueous  solution ;  and  accordingly  it 
is  found  that,  when  the  quantities  of  heat  evolved  by  the  com- 
bination of  different  bases  and  acids  (or  metals  and  radicals), 
in  the  form  of  soluble  salts,  are  compared,  numbers  are 
obtained  which  exhibit  a  tolerably  near  approach  to  regular 
progression. 

The  following  Table  exhibits  the  number  of  units  of  heat 
evolved  by  equivalent  quantities  of  different  bases  in  com- 
bining with  various  acids,  as  determined  by  Favre  and  Silber- 
mann :  — 


Bases. 

Acids. 

Sul- 
phuric. 

Nitric. 

Hydro- 
cliloric. 

Hydro- 
bromic. 

Hy- 

driodic. 

Acetic. 

Grm. 

47-2  Potash  . 

31     Soda      . 

26     Oxide  of  ammonium     . 

76-5  Baryta 

28     Lime     . 

20     Magnesia      .     . 

35-6  Manganous  oxide 

40-6  Zinc-oxide 

64     Cadmic  oxide    . 

39'7  Cupric  oxide     . 

37-6  Nickel-oxide      . 

37  "5  Cobaltous  oxide 
111-7  Lead-oxide 
116-1  Silver-oxide       . 

16083 
15810 
14690 

14440 
12075 
10455 
10240 
7720 
11932 
11780 

15510 

15283 

13676 

15360 

16943 

12840 

10850 

8323 

8116 

6400 

10450 

9956 

9240 

6206 

15656 

15128 

13536 

15306 

16982 

13220 

11235 

8307 

8109 

6416 

10412 

10374 

15510 
15159 

15698 
15097 

13978 

13600 

12649 

13262 

14675 

12270 

9982 

7720 

7546 

5264 

9245 

9272 

7168 

A  comparison  of  these  numbers  shows  that  nitric,  hydro- 
chloric, hydrobromic,  and  hydriodic  acids,  in  combining  with 
the  same  base,  evolve  nearly  equal  quantities  of  heat;  sul- 


X  X  2 


632  HEAT   OF   CHEMICAL   COMBINATION. 

phuric  acid  a  considerably  greater,  and  acetic  acid  a  smaller 
quantity.  Among  the  bases,  the  alkalies  evolve  the  greatest 
quantity  of  heat  in  combining  with  any  acid.  In  general,  it 
appears  that  the  greatest  heat  is  evolved  by  the  combination 
of  the  strongest  acids  with  the  strongest  bases. 

The  corresponding  terms  of  any  two  horizontal  rows  in  the 
preceding  table  exhibit,  in  some  cases,  nearly  equal  differ- 
ences ;  and  the  same  is  true  with  regard  to  the  corresponding 
terms  of  any  two  vertical  rows.  If  these  differences  were 
constantly  equal,  it  would  follow  that  the  quantities  of  heat 
evolved  or  absorbed  in  the  substitution  of  a  base  a  for  a 
base  b  (potash  for  soda,  for  example),  would  be  the  same 
with  whatever  acid  the  base  were  united  ;  and,  similarly,  the 
heat  evolved  or  absorbed  in  the  substitution  of  one  particular 
acid  for  another,  would  be  independent  of  the  bases.  The 
actual  differences,  however,  deviate  too  much  from  this  law 
to  warrant  its  reception  as  an  expression  of  the  results  of 
observation.  Nevertheless,  there  is  a  considerable  degree  of 
a  priori  probability  in  its  favour ;  and  the  observed  deviations 
from  it  may  perhaps  arise  from  disturbing  causes,  such  as 
the  different  quantities  of  heat  absorbed  in  the  solution  of 
salts,  &c.  How  far  this  is  the  case,  remains  to  be  decided 
by  further  experiments. 

Heat  is  likewise  evolved  in  the  combination  of  acids  with 
water.  The  following  are  the  quantities  of  heat  developed, 
according  to  Favre  and  Silbermann,  by  mixing  sulphuric 
acid,  SO4H,  with  various  proportions  of  water. 


Heat-units.  Differences. 


With  the  first      ^  atom  water  .         .         .         .         9*4 ")     q- 

,,  .         .         .         ,         .         8'8J 


second  i 


first      \  „ 18-8  "1 

second  ^  „ 172 J 

first       ^  „ 3G-7\     .. 

second^  „ 28-3  J 


HEAT   OF   CHEMICAL   COMBINATION.  633 


Heat-units.  Differences. 

With  1  atom  water 64-7 

2 94-6 


3 

4 
.5 
6 
7 
8 
9 
10 
20 


111 

122-2 

1307 

136-2 

141-8 

145-1 


.9}    ^^• 

.0}  10- 


29-9 
•3 
3 
8-5 
5-5 
4-4 
3-3 
3-4 


148-5  , 

148-4}    0-0 

148-6 


0-0 


These  numbers  show  that  the  heat  evolved  by  adding  a 
given  quantity  of  water  to  hydrated  sulphuric  acid,  diminishes 
as  the  quantity  of  water  already  present  is  greater. 

Heat  evolved  hy  the  solution  of  gases  in  water,  —  When  a  gas 
dissolves  in  water,  heat  is  evolved,  partly  in  consequence  of 
the  chemical  combination,  and  partly  from  the  condensation 
of  the  gas  to  the  liquid  state.  According  to  Favre  and  Sil- 
bermann :  — 

Heat-units, 
gramme  of  hydrochloric  acid  gas  dissolved  in  water  evolves  449-6 
„  hydrobromic         „  „  „         235*6 

„  hydriodic  „  „  „         147-7 

„  sulphurous  „  „  „         120*4 

„  amraoniacal  gas  „  „  „         514*3 

The  heat  evolved  varies,  however,  according  to  the  quantity 
of  water  in  which  a  given  quantity  of  the  gas  dissolves. 

Solution  of  salts,  Sfc,  in  water. — The  calorific  effect  pro- 
duced by  the  solution  of  a  solid  in  a  liquid,  depends  upon 
several  circumstances ;  viz.  on  the  chemical  affinity  between 
the  two,  on  the  quantity  of  heat  absorbed  in  the  passage  of 
the  solid  to  the  liquid  state,  on  the  quantity  of  the  solvent, 
and  on  the  temperature  at  which  the  solution  takes  place. 
The  result  is,  in  most  cases,  an  absorption  of  heat  or  reduc- 
tion of  temperature ;  in  some  cases,  however,  as  when  the 
act  of  solution  is  preceded  or  accompanied  by  the  formation 
of  a  definite  hydrate,  the  effect  may  be  reversed.  The  com- 
bination of  anhydrous  potash  with  water  to  form  the  hydrate 

X  X  3 


634 


HEAT   OF   CHEMICAL   COMBINATION. 


KO  .  HO,  is  attended  with  a  rise  of  temperature  sufficient  to 
produce  incandescence  ;  the  hydrate  KO  .  HO  likewise  evolves 
a  considerable  quantity  of  heat  on  dissolving  in  water,  because 
it  first  combines  with  a  definite  proportion  of  water,  forming 
the  hydrate  KHO2.4HO;  but  the  solution  of  this  latter 
compound  in  water  produces  a  considerable  fall  of  tempera- 
ture. Anhydrous  chloride  of  calcium  combines  with  water, 
forming  the  hydrate  CaCl .  6H0,  the  combination  being 
attended  with  great  evolution  of  heat;  but  the  solution  of 
the  hydrate  in  water  produces  cold. 

The  absorption  of  heat  accompanying  the  solution  of  salts 
is  not  wholly  due  to  the  liquefaction  of  the  solid  ;  for  the  heat 
thus  absorbed  in  solution  is  sometimes  greater,  sometimes 
less  than  when  the  salt  is  liquefied  by  heat  alone.  Thus,  in 
the  fusion  of  1  gramme  of  nitrate  of  potash,  49  heat-units 
are  rendered  latent;  but  when  the  same  salt  is  dissolved  in 
20  parts  of  water,  at  20°  C,  80  heat-units  are  absorbed.  The 
latent  heat  of  fusion  of  crystallised  chloride  of  calcium  is  41 
heat-units ;  but  when  this  hydrated  salt  dissolves  in  12 
parts  of  water  at  8°  C,  only  19  heat-units  are  absorbed.  (0. 
Person.*) 

The  following  results  are  extracted  from  Person's  deter- 
minations of  the  influence  of  the  temperature  and  quantity  of 
the  solvent  on  the  quantity  of  heat  absorbed  :  — 


Name  of  Salt. 

Quantity  of 
Water. 

Temperature. 

Units  oflleat 
absorbed. 

Chloride  of  sodium  .    .     1  gramme  -I 
Nitrate  of  soda    ...            „         j 

Nitrate  of  potash     .    .           "        -f 

7-28 
7-28 
7-28 

5 

20 

10 
10 
20 
20 

17-1  C. 
10-3 
0-2 

22-7 
22-8 

23-8 

5-5 

5-7 
19-7 

13',') 
14-9 

18-7 

47-1 
55-7 

76-7 
80-2 
86-4 
80-5 

Ann.  Ch.  Thys.  [3],  xxxiii.  448. 


COLD  PRODUCED  BY  CHEMICAL  DECOMPOSITION.      635 

Hence  it  appears  that  when  a  given  quantity  of  a  salt  is 
dissolved  in  the  same  quantity  of  water  at  different  tem- 
peratures, the  quantity  of  heat  absorbed  is  greater  as  the 
initial  temperature  is  lower ;  and  at  the  same  temperature, 
the  quantity  of  heat  absorbed  increases  with  the  quantity  of 
the  solvent.  A  fall  of  temperature  is  sometimes  produced  by 
merely  diluting  a  solution  with  water.     (Person.) 


COLD   PRODUCED   BY   CHEMICAL   DECOMPOSITION. 

The  separation  of  any  tivo  bodies  is  attended  ivith  the  ahsorp- 
tion  of  a  quantity  of  heat  equal  to  that  luhich  is  evolved  in  their 
combination.  The  truth  of  this  proposition  has  been  estab- 
lished by  Dr.  Woods  *  and  Mr.  Joule  f,  by  comparing  the  heat 
evolved  in  the  electrolysis  of  water,  with  that  which  is  de- 
veloped in  a  thin  metallic  wire  by  a  current  of  the  same 
strength.  The  current  was  first  made  to  pass  through  a 
vessel  containing  acidulated  water,  the  quantity  of  gas 
evolved  in  a  given  time  determined,  and  also  the  rise  of 
temperature,  the  strength  of  the  current  being  at  the  same 
time  measured  by  the  tangent-compass  (p.  497).  The  elec- 
trolytic cell  was  then  removed,  and  a  thin  platinum  wire 
introduced  between  the  poles,  of  such  a  length  as  to  produce 
a  resistance  equal  to  that  of  the  electrolyte.  The  quantity  of 
heat  evolved  in  this  wire  was  then  determined,  and  found 
to  exceed  that  which  was  previously  evolved  in  the  electro- 
lytic cell,  by  a  quantity  equal  to  that  which  would  be  evolved 
in  the  combination  of  the  oxygen  and  hydrogen  eliminated  by 
the  current  in  the  previous  experiment. 

The  same  proposition  is  likewise  established  by  many  other 
chemical  phenomena.  When  zinc  dissolves  in  dilute  sulphuric 
acid,  the  action  may  be  supposed  to  consist  of  three  stages, 
viz,  the  decomposition  of  w^ater,  the  formation  of  oxide  of 

*  Phil.  Mag.  [4],  ii.  368. 
t  Pliil.  Mag.  [4],  iii.  481. 
XX  4 


636      COLD  PRODUCED  BY  CHEMICAL  DECOMPOSITION. 

zinc,  and  the  combination  of  the  oxide  of  zinc  with  sulphuric 
acid,  forming  ZnO  .  SO3.     Now  : 

Ileat-uiiits. 
The  heat  evolved  in  the  oxidation  of  1  atom  or  32*6  parts  of  zinc    .     =  42413 
The  heat  evolved  in  the  combination  of  1  atom  or  40*6  parts  oxide 
of  zinc  with  sulphuric  acid,  in  presence  of  a  large  quantity  of 
water  (p.  631)     .......=  10455 

Sumt  .      =  52868 
Deducting  from  this  the  heat  evolved  in  the  combination  of  1  atom 

or  1  gramme  of  hydrogen  with  oxygen    .  .  .  .=  34462 

There  remains  for  the  heat  evolved  in  the  entire  process       .  .         18406 

which  agrees  very  nearly  with  the  quantity  determined  by 
direct  experiment,  viz.  18,514  heat-units. 

Again,  when  metallic  oxides  are  reduced  by  hydrogen,  the 
heat  evolved  is  not  so  great  as  when  the  same  quantity  of 
hydrogen  combines  with  free  oxygen,  because  it  is  diminished 
by  the  heat  absorbed  in  the  separation  of  the  oxygen  and  the 
metal. 

The  reduction  of  oxide  of  iron  by  hydrogen  takes  place 
without  much  evolution  of  heat,  because  the  heat  evolved  in 
the  combination  of  1  grm.  of  oxygen  with  hydrogen,  viz. 
4308  heat-units  (p.  627),  is  not  much  greater  than  that  which 
is  evolved  when  the  same  quantity  of  oxygen  combines  with 
iron,  viz.  4134  heat-units.  But  the  reduction  of  oxide  of 
copper  is  attended  with  a  rise  of  temperature  amounting  to 
incandescence,  because  the  heat  evolved  in  the  oxidation  of 
hydrogen  greatly  exceeds  that  which  is  evolved  in  the  oxida- 
tion of  copper,  which  is  only  2393  heat-units. 

The  absorption  of  heat  in  decomposition  is  also  demon- 
strated by  the  fact  that  no  alteration  of  temperature  takes 
place  in  the  double  decomposition  of  salts,  provided  all  the 
products  remain  in  solution ;  in  fact,  the  heat  evolved  in  the 
combinations  is  exactly  compensated  by  the  cold  produced  by 
the  decompositions  which  take  place  at  the  same  time.  But 
if  a  precipitate  is  formed,  heat  is  evolved,  in  consequence  of 


COLD  PRODUCED  BY  CHEMICAL  DECOMPOSITION.   637 

the  passage  of  the  compound  from  the  liquid  to  the  solid 
state. 

There  are  some  phenomena  which  appear  to  contradict  the 
assertion  that  heat  is  always  absorbed  in  chemical  decomposi- 
tion. The  decomposition  of  some  of  the  oxides  of  chlorine, 
and  of  the  chloride  and  iodide  of  nitrogen,  is  attended  with 
evolution  of  heat.  It  has  also  been  shown  by  Favre  and 
Silbermann,  that,  in  the  combustion  of  charcoal  in  nitrous 
oxide,  more  heat  is  evolved  than  when  charcoal  burns  in 
pure  oxygen  ;  and  that  the  decomposition  of  peroxide  of  hy- 
drogen by  platinum  is  attended  with  considerable  rise  of  tem- 
perature. These  apparent  anomalies  may,  however,  be  re- 
conciled with  the  general  law,  if  we  admit  that  all  chemical 
actions  may  be  regarded  as  double  decompositions  (pp.  517 — 
520).  Thus,  in  the  last  case,  regarding  peroxide  of  hydrogen 
as  water  plus  oxygen,  the  decomposition  may  be  represented 
by  the  equation  :  — 

HO.O   +  HO.O  =  2H0   +   00. 

And  it  is  possible  that  the  heat  evolved  in  the  combination  of 
oxygen  with  oxygen,  may  be  greater  than  that  which  is  ab- 
sorbed in  the  separation  of  the  oxygen  from  the  water ;  and 
similarly  in  the  other  cases. 


638 


NON-METALLIC  ELEMENTS. 


OXYGEN  AND   HYDROGEN. 

Extraction  of  Oxygen  from  Atmospheric  air.  —  Boussingault 
lias  shown*  that  it  is  possible  to  obtain  oxygen  gas  in  con- 
siderable quantity  from  the  air  by  the  use  of  baryta,  that 
substance  absorbing  oxygen  from  the  air  at  a  low  red  heat, 
and  being  converted  into  peroxide  of  barium,  and  the  latter, 
when  raised  to  a  higher  temperature,  —  or  still  more  easily 
when  exposed  to  a  current  of  aqueous  vapour, — giving  up  its 
second  atom  of  oxygen  in  the  free  state.  The  apparatus  used 
consists  of  a  tube  of  porcelain  or  glazed  earthenware,  com- 
municating at  the  one  end,  by  means  of  smaller  tubes  provided 
with  stopcocks,  with  an  aspirator  and  a  gas-holder,  and  at  the 
other  with  the  external  air  and  also  with  a  steam-boiler.  The 
tube  is  filled  with  hydrate  of  baryta, — mixed  with  lime  or 
magnesia  to  diminish  its  fusibility, — and  heated  to  low  red- 
ness, a  current  of  air  being  at  the  same  time  drawn  through 
the  tube  by  the  aspirator.  The  hydrate  of  baryta  is  thereby 
converted  into  peroxide  of  barium ;  and  when  the  oxidation 
has  proceeded  far  enough,  the  current  of  air  is  suspended,  a 
jet  of  steam  sent  through  the  tube,  and  at  the  same  time  the 
connection  with  the  gas-holder  is  opened ;  the  peroxide  of 
barium  is  then  reconverted  into  hydrate  of  baryta,  and  the 
excess  of  oxygen  passes  into  the  gas-holder.     The  hydrate  of 

*  Compt.  rend,  xxxii.  2G1  ;  Ann.  Ch.  Phys.  [3],  xxx.  5 ;  Clicm.  Soc.  Qu.  J. 
V.  269. 


EXTRACTION  OF  OXYGEN  FROM  THE  AIR.     639 

baryta  may  now  be  reoxidised  by  a  fresh  current  of  air,  the 
resulting  peroxide  again  decomposed  by  vapour  of  water,  — 
and  this  series  of  operations  may  be  repeated  any  number  of 
times.  Boussingault's  first  experiments  were  made  with  an- 
hydrous baryta,  which  Hkewise  absorbs  oxygen  when  heated 
to  low  redness  in  a  current  of  air,  and  gives  it  up  again  at  a 
bright  red  heat.  It  was  found,  however,  that  the  baryta, 
after  one  or  two  repetitions  of  the  process,  lost  in  a  great 
measure  its  power  of  absorbing  oxygen.  In  fact,  baryta, 
when  really  anhydrous,  shows  but  little  inclination  to  absorb 
oxygen  ;  it  is  only  the  hydrate  that  is  readily  converted  into 
BaOg.  Now  baryta,  when  prepared  in  the  ordinary,  way,  by 
calcining  the  nitrate,  always  contains  a  little  water,  which 
facilitates  the  absorption  of  the  oxygen;  but  after  being 
heated  two  or  three  times  in  a  current  of  dry  air,  it  becomes 
really  anhydrous,  and  is  then  no  longer  oxidised.  The  use  of 
hydrate  of  baryta  is  therefore  much  more  advantageous,  both 
for  the  reason  just  stated,  and  likewise  because  the  decom- 
position of  the  peroxide  by  vapour  of  water  takes  place  at  a 
much  lower  temperature  than  by  simple  ignition.  The  pro- 
cess in  this  form  is  adapted  for  use  on  the  large  scale.* 

Ozone  (I.  304).  —  The  nature  of  ozone  is  still  a  matter  of 
discussion.  That  it  is  a  higher  oxide  of  hydrogen  was  first 
suggested  by  Professor  Williamson  f,  who  passed  ozoniferous 
oxygen,  obtained  by  electrolysis,  first  over  chloride  of  calcium 
to  dry  it,  and  then  through  a  glass  tube,  in  which  it  was  either 
heated  by  a  spirit-lamp  or  brought  in  contact  with  finely 

*  A  patent  for  the  preparation  of  oxygen  in  this  manner,  and  its  application 
in  various  chemical  operations,  has  been  taken  out  by  Messrs.  Swindells  and 
Nicholson.     (Chem.  Gaz.  1855,  139.) 

f  Ann.  Ch.  Pharm.  liv.  127.  This  view  was  afterwards  adopted  by 
Schonbein  (Pogg.  Ann.  Ixvii.  78),  but  he  has  since  abandoned  it,  inclining 
rather  to  regard  ozone  as  an  allotropic  modification  of  oxygen  (^Atm.  Ch, 
Pharm.  Ixxxii.  222  ;  J.  pr.  Chem.  liii.  65). 


640  OXYGEN   AND   HYDROGEN. 

divided  copper  at  a  red  heat.  The  ozone  was  thereby  decom- 
posed and  deprived  of  its  odour,  and  water  was  deposited. 
The  same  view  has  been  further  supported  by  the  more 
recent  experiments  of  Baumert*,  who  has  likewise  analysed 
the  ozone  quantitatively,  and  finds  that  it  is  a  teroxide  of 
hydrogen,  HO3.  In  Baumert's  experiments,  ozoniferous  oxygen, 
evolved  at  the  positive  pole  from  water  acidulated  with  sul- 
phuric and  chromic  acids  (which  mixture  was  found  to  yield 
the  largest  quantity  of  ozone,  not,  however,  exceeding  1  milli- 
gramme of  that  substance  to  3^  litres  of  oxygen)  was  passed, 
after  thorough  drying,  into  a  glass  tube  lined  with  a  film  of 
anhydrous  phosphoric  acid.  On  heating  the  tube  with  a 
spirit-lamp,  the  phosphoric  acid  became  transparent,  and  was 
dissolved  at  the  part  of  the  tube  beyond  the  flame,  showing  that 
water  was  there  deposited.  It  would  appear  then  that  ozone, 
obtained  by  electrolysis,  contains  the  elements  of  water ;  and 
its  powerful  oxidising  properties  show  that  it  also  contains  an 
excess  of  oxygen.  Hence,  to  analyse  it  quantitatively,  it  is 
only  necessary  to  determine  the  proportion  of  this  excess  of 
oxygen  in  a  known  weight  of  ozone.  The  analysis  was  made 
by  passing  the  ozoniferous  oxygen,  first  through  a  tube  con- 
taining pumice-stone  soaked  in  sulphuric  acid,  to  dry  it ; 
then  through  a  bulb- apparatus  containing  solution  of  iodide 
of  potassium,  which  completely  absorbed  the  ozone,  and  was 
itself  at  the  same  time  partially  decomposed,  a  certain  quan- 
tity of  iodine  being  set  free  by  the  excess  of  oxygen  in  the 
ozone  ;  and,  lastly,  through  a  second  bulb-apparatus  contain- 
ing strong  sulphuric  acid,  to  absorb  any  water  mechanically 
carried  forward  from  the  iodide  of  potassium  solution  by  the 
stream  of  gas.  The  increase  of  weight  in  the  two  bulb- 
apparatus  gave  the  total  quantity  of  ozone ;  and  the  quantity 
of  iodine  set  free  (estimated  by  Bunsen's  volumetric  method  f) 

*  Pogg.  Ann.  Ixxxix.  38  ;  Chcm.  Soc.  Qu.  J.  vi.  169. 
f  Ann.  Ch.  Pharm.  Ixxxvi.  265. 


OZONE,  641 

determined  the  amount  of  active  oxygen  therein.  Two  ex- 
periments made  in  this  manner  gave  in  100  parts  of  ozone : — 
96-24  O  +  3-76  H,  and  95-70  O  +  4-30  H  respectively.  The 
formula,  HOg,  requires  95*66  O  +  4-34  H.  The  oxidising 
action  of  the  ozone  was  found  to  be  so  powerful,  that  it  quickly 
destroyed  any  organic  substance,  such  as  vulcanised  caout- 
chouc, used  to  connect  the  different  parts  of  the  apparatus : 
hence  it  was  necessary  to  make  all  the  connections  either  by 
fusion  or  by  grinding. 

Baumert  has  also  found,  in  accordance  with  the  observa- 
tions of  previous  experimenters,  that  perfectly  dry  oxygen 
gas,  subjected  for  some  time  to  the  action  of  the  electric  spark, 
is  brought  into  an  allotropic  state,  in  which  its  combining 
tendencies  are  highly  exalted,  so  that  it  is  capable  of  over- 
coming the  most  powerful  affinities,  such  as  that  of  chlorine 
or  iodine  for  potassium,  at  ordinary  temperatures.  Ozonised 
oxygen  was  freed  from  ozone  and  aqueous  vapour  by  passing 
through  sulphuric  acid,  through  a  heated  glass  tube,  over 
fragments  of  iodide  of  potassium,  and  through  pulverulent 
phosphoric  acid,  and  then  made  to  pass  through  a  glass  tube 
having  platinum  wires  fixed  into  its  sides.  On  passing  a  rapid 
succession  of  electric  sparks  between  these  wires,  the  gas  ac- 
quired again  the  odour  of  ozone,  and  the  power  of  decomposing 
a  solution  of  iodide  of  potassium,  characters  which  it  did  not 
possess  before  the  sparks  were  passed  through  it.  When 
heated  to  200°  C.  it  lost  these  peculiar  properties,  and  was 
restored  to  its  ordinary  state.  Results  similar  to  this  had 
previously  been  obtained  by  Marignac  and  De  la  Rive,  and 
also  by  Fremy  and  Becquerel.*  In  the  experiments  of  the 
last-mentioned  philosophers,  perfectly  dry  oxygen  gas,  enclosed 
in  sealed  glass  tubes,  and  subjected  to  the  continued  action  of 
electric  sparks  passed  along  the  outer  surface  of  the  glass,  was 
found  to  acquire  the  power  of  decomposing  iodide  of  potassium, 

*  Ann.  Cli.  rhys.  [3],  xxxv.  62  j  Chem.  Soc.  Qu.  J.  v.  272, 


042  OXYGEN   AND   HYDROGEN. 

and  was  absorbed  by  moist  mercury  or  silver,  and  by  solu- 
tion of  iodide  of  potassium.  From  these  experiments  it  may 
be  reasonably  concluded  that  oxygen  can  by  certain  means  be 
brought  into  a  modified,  and  excited  condition;  but  as  this 
modified  oxygen,  when  it  exhibits  the  odour  of  ozone,  or  any  of 
its  peculiar  reactions,  is  necessarily  brought  into  contact  with 
moisture,  it  is  likewise  highly  probable  that  it  then  combines 
with  the  elements  of  water,  forming  the  true  ozone  IIO3, 
and  that  to  this  the  odour  and  oxidising  actions  are  really 
due. 

Ozone,  formed  by  the  slow  oxidation  of  phosphorus  in  the 
air,  exhibits  the  same  characters  as  that  which  is  obtained  by 
electrolysis  of  water,  &c.  Ozone  thus  produced  is  generally 
regarded  as  merely  allotropic  oxygen ;  but  as  water  is  always 
present  in  its  formation,  it  may  also  be  a  peroxide  of  hydrogen, 
like  the  ozone  obtained  from  electrical  sources.* 

According  to  Schonbein,  many  other  substances  besides 
phosphorus  possess  the  power  of  inducing  the  formation  of 
ozone.  Thus,  ether,  oil  of  turpentine,  oil  of  lemons,  linseed 
oil,  alcohol,  wood-spirit,  various  vegetable  acids,  sulphuretted 
hydrogen,  arseniuretted  hydrogen,  and  sulphurous  acid,  in 
contact  with  air  or  oxygen  gas,  and  under  the  influence  of 
light,  acquire  the  power  of  decolorising  indigo,  and  producing 
various  oxidising  actions.  A  similar  influence  is  exerted  by 
mercury  and  other  noble  metals  in  the  finely  divided  state; 
and  stibethyl  is  found  to  be  a  more  powerful  ozoniser  than 
even  phosphorus  itself. 

Houzeau  has  shown  f  that  active  oxygen  may  be  obtained 
by  the  action  of  strong  (monohydrated)  sulphuric  acid  on 
peroxide  of  barium.  The  gas  thus  evolved  has  a  very 
powerful  odour,  and  a  taste  like  that  of  the  lobster  ;  it 
rapidly  decolorises  blue  litmus  paper ;  oxidises  silver ;  burns 

*  Williamson,  Ann.  Ch.  riiarra.  Ixi.  32. 
f  Compt.  rend.  xl.  947. 


OZONE,  643 

ammonia  spontaneously,  transforming  it  into  nitrate  of  am- 
monia; instantly  burns  phosphurettecl  hydrogen  (the  less 
inflammable  variety,  I.  451)  with  emission  of  light;  de- 
composes hydrochloric  acid,  setting  the  chlorine  free ;  is 
a  powerful  oxidising  and  chlorinising  agent;  is  stable  at 
ordinary  temperatures,  but  loses  its  peculiar  properties  when 
heated  to  75°  C.  In  all  these  respects,  it  differs  essentially 
from  ordinary  oxygen ;  in  fact  it  exhibits  the  properties  of 
ozone.  Active  oxygen  may  also  be  obtained  from  other 
bodies  besides  the  peroxide  of  barium.  Oxygen  in  the  com-* 
bined  state  appears,  indeed,  to  possess  the  intensified  power 
which  distinguishes  free  oxygen  in  the  nascent  state. 

The  nature  of  ozone  has  also  been  investigated  by  Dr. 
Andrews*,  who  has  arrived  at  the  conclusion  that  electrolytic 
ozone,  as  well  as  that  obtained  from  other  sources,  is  nothing 
but  active  oxygen.  The  excess  of  the  weight  of  ozone  in 
Baumert's  experiments,  over  that  of  the  active  oxygen,  is 
attributed  by  Andrews  to  the  presence  of  a  small  quantity  of 
carbonic  acid,  which  he  states  is  always  mixed  with  the 
gases  resulting  from  the  decomposition  of  water,  unless  espe- 
cial precautions  be  taken  to  get  rid  of  it,  and  being  absorbed 
by  the  potash  resulting  from  the  decomposition  of  the  neutral 
solution  of  iodide  of  potassium,  increases  the  weight  of  the 
apparatus,  and  consequently  produces  an  apparent  increase  in 
the  quantity  of  ozone  absorbed. 

To  obviate  this  supposed  source  of  inaccuracy,  Andrews, 
using  an  apparatus  similar  to  that  of  Baumert,  acidulated  his 
solution  of  iodide  of  potassium  with  hydrochloric  acid ;  and, 
in  five  experiments,  in  which  29  litres  of  the  ozoniferous  gas 
were  passed  through  the  apparatus,  obtained  an  increase  of 
weight  in  the  absorption-bulbs,  that  is  to  say,  a  quantity  of 
ozone  —  amounting  to  0*1179  grm.,  while  the  quantity  of 
active  oxygen,  estimated  according  to  the  quantity  of  iodine 
*  Chera.  Soc.  Qu.  J.  ix.  168. 


644  OXYGEN   AND   HYDROGEN. 

separated,  was  0*1178  grm.  From  this  result,  Andrews  con- 
cludes that  ozone  is  nothing  but  an  active  form  of  oxygen. 

In  another  series  of  experiments,  in  which  electrolytic 
ozone  was  decomposed  by  heat,  and  the  gas  subsequently 
passed  over  strong  oil  of  vitriol  and  anhydrous  phosphoric 
acid,  not  a  trace  of  water  could  be  discovered.  Andrews 
has  likewise  confirmed  the  result  obtained  by  other  experi- 
menters that  pure  dry  oxygen  acquires  peculiar  active  pro- 
perties by  the  action  of  the  electric  spark ;  and  by  comparing 
the  properties  of  ozone  obtained  from  various  sources,  he 
concludes  that  ozone,  in  whatever  manner  produced,  is  es- 
sentially the  same,  consisting  in  fact  of  allotropic  oxygen. 

On  the  other  hand,  Baumert  *  denies  the  existence  of  car- 
bonic acid  in  the  ozoniferous  gas  which  he  obtained  by  elec- 
trolysis, inasmuch  as  the  electrolyte  used,  water  acidulated 
with  sulphuric  and  chromic  acid,  could  scarcely  absorb  a 
sufficient  quantity  of  carbonic  acid  to  account  for  the  results 
obtained.  He  moreover  attributes  the  carbonic  acid  which 
Andrews  obtained,  to  the  oxidising  action  of  the  ozone  on  the 
diaphragm  of  bladder  with  whicli  the  positive  cell  of  the 
decomposing  apparatus  was  closed.  Baumert  finds,  indeed, 
that  when  a  diaphragm  of  bladder  is  used  for  this  purpose, 
carbonic  acid  is  actually  produced  ;  but  when  a  diaphragm  of 
gypsum  is  employed,  not  a  trace  of  that  gas  can  be  detected. 
With  respect  to  the  use  of  iodide  of  potassium  acidulated 
with  hydrochloric  acid,  Baumert  calls  attention  to  the  fact 
that  such  a  solution  must  contain  free  hydriodic  acid,  which  is 
decomposed  by  oxygen  in  its  ordinary  as  well  as  in  its  allo- 
tropic state.  In  fact,  oxygen  gas  evolved  by  electrolysis,  and 
completely  freed  from  ozone  by  passing  through  a  neutral 
solution  of  iodide  of  potassium,  liberated,  when  subsequently 
passed  through  a  solution  of  the  same  salt  acidulated  with 
hydrochloric  acid,  a  quantity  of  iodine  much  larger  than 
that  which   it  had   previously  separated   from   the   neutral 

*  Pogg.  Ann.  xcix.  88. 


ESTIMATION   OF   OXYGEN   AND   HYDROGEN.  645 

solution.  This  may  account  for  the  greater  proportion  of 
the  active  oxygen  to  the  total  quantity  of  ozone  obtained  in 
the  experiments  of  Andrews. 

The  true  nature  of  ozone  must  then  still  be  considered  a 
matter  for  investigation.  The  existence  of  an  allotropic 
modification  of  oxygen  possessing  peculiarly  active  properties 
appears  to  be  established  by  the  researches  of  numerous 
inquirers ;  but  on  the  other  hand,  till  some  more  valid  ob- 
jection is  adduced  against  the  results  obtained  by  Baumert  and 
Williamson,  the  existence  of  hydrogen  in  the  ozone  obtained 
by  electrolysis  of  acidulated  water  can  scarcely  be  denied. 

Quantitative  estimation  of  Oxygen  and  Hydrogen,  —  Tlie 
quantity  of  either  of  these  gases  in  a  gaseous  mixture  may  be 
determined  by  mixing  it  with  an  excess  of  the  other,  and 
inducing  combination  by  the  electric  spark,  or  by  spongy  plati- 
num or  platinised  charcoal.  One-third  of  the  volume  of  gas 
which  disappears  is  oxygen,  and  two-thirds  hydrogen.  This, 
of  course,  implies  that  no  other  gases  are  present  capable  of 
uniting  with  either  oxygen  or  hydrogen. 

The  amount  of  hydrogen  in  solid  or  liquid  compounds 
(generally  organic),  when  it  is  not  present  in  the  form  of 
water,  is  estimated  by  heating  the  compound  in  contact  with 
some  oxidising  agent,  generally  oxide  of  copper,  and  weigh- 
ing the  water  produced  (p.  662).  Oxygen  in  such  compounds 
is  generally  determined  by  loss,  the  quantities  of  all  the  other 
elements  being  determined  by  the  methods  severally  applicable 
to  them,  and  the  remainder  being  estimated  as  oxygen.  The 
quantity  of  oxygen  in  metallic  oxides  which  are  not  reduced 
by  heat  alone,  is  generally  estimated  by  igniting  them  in  a 
current  of  hydrogen  and  weighing  the  water  produced. 

The  quantity  of  oxygen  in  the  atmosphere  may  be  deter- 
mined by  methods  already  described  (I.  331).  A  very  good 
method  has  since  been  given  by  Liebig*,  viz.  to  absorb  the 

*  Chem.  Soc.  Qu.  J.  iv.  221. 
VOL.  II.  Y  Y 


646  OXYGEN   AND   HYDROGEN. 

oxygen  by  means  of  an  alkaline  solution  of  pyrogallate  of 
potash.  Pyrogallic  acid  is  readily  obtained  as  a  crystalline 
sublimate  by  the  dry  distillation  of  gallic  acid;  it  dissolves 
easily  in  potash :  and  the  solution  introduced  by  means  of  a 
pipette  into  air  standing  over  mercury,  absorbs  the  oxygen 
quickly  and  completely. 

Estimation  of  Water, — The  quantity  of  water  in  a  solid 
compound,  a  salt  for  example,  is  determined  by  heating  a 
weighed  quantity  of  the  substance  in  a  capsule  or  crucible 
over  a  lamp,  or  in  a  sand-bath,  or  over  a  water-bath,  accord- 
ing to  the  temperature  which  it  will  bear  without  giving  off 
anything  but  water.  Substances  which  will  not  bear  even 
the  temperature  of  the  water-bath,  are  dehydrated  by  placing 
them  over  strong  sulphuric  acid,  sometimes  in  vacuo,  sometimes 
by  merely  placing  the  dish  containing  the  sulphuric  acid,  with 
the  substance  supported  above  it  in  a  capsule,  on  a  ground 
glass  plate,  and  covering  the  whole  with  a  bell  jar.  Another 
method  of  drying  substances  which  will  not  bear  much  heat, 
is  to  place  them  in  a  bent  tube  immersed  in  a  water-bath  at  a 
regulated  temperature,  and  pass  through  the  tube  a  current  of 
dry  air,  hydrogen,  or  carbonic  acid,  according  to  the  nature 
of  the  substance. 

Some  salts  when  heated  give  off  a  portion  of  their  acid  as 
well  as  their  water,  the  sulphates  of  alumina,  and  sesquioxide  of 
iron  for  example.  To  determine  the  quantity  of  water  in  such 
cases,  the  salt  must  be  mixed  with  a  weighed  quantity  of 
protoxide  of  lead,  sufficient  to  cover  it  completely,  and  heated 
in  a  platinum  crucible :  the  acid,  which  would  otherwise 
escape,  is  then  retained  by  the  oxide  of  lead,  and  nothing  but 
water  goes  off. 

The  quantity  of  combined  water  in  a  base,  such  as  hydrate 
of  potash,  is  determined  by  heating  the  base  with  an  acid  which 
will  form  with  it  a  compound  not  decomposable  at  a  red  heat. 

In  all  cases,  the  water,  instead  of  being  estimated  merely 
by  loss  of  weight,  may  be  determined  by  receiving  it  in  a 
tube  filled  with  dry  chloride  of  calcium,  or   with   pumice 


ABSORrXION    OP^    GASES.  64^ 

stone  soaked  in  strong  sulphuric  acid,  an  empty  glass  bulb, 
previously  weighed,  being,  however,  interposed  when  the 
quantity  of  water  is  large  (Vol.  I.  p.  313,  fig.  102).  This 
method  is  particularly  applicable  when  other  substances  be- 
sides water  are  given  off  at  the  same  time. 

The  methods  of  determining  the  quantity  of  water  in  solu- 
tions are  similar  to  those  above  described  for  solids  (I.  545). 

Absorption  of  gases  by  water  and  other  liquids. — The  laws 
relating  to  the  absorption  of  gases  by  liquids  have  lately  been 
examined  with  great  care  by  Bunsen,  whose  results  tend 
partly  to  coniSrm,  partly  to  modify  those  of  the  older  experi- 
ments of  Dalton,  Henry,  and  Saussure  (I.  75,  316). 

The  absorption  of  the  more  soluble  gases,  such  as  am- 
monia, sulphurous  acid,  &c.,  was  estimated  by  saturating  the 
liquid  with  the  gas  at  a  known  temperature,  and  then  de- 
termining, either  by  volumetric,  or  by  weighed  analyses,  the 
quantity  of  gas  dissolved  in  a  given  volume  of  the  liquid ;  for 
example,  hydrosulphuric  acid  was  precipitated  by  a  solution 
of  copper,  sulphurous  acid  and  chlorine  were  determined  by 
the  iodometric  method,  to  be  afterwards  described. 

For  the  less  soluble  gases,  a  different  method  was  adopted. 
The  apparatus  used  for  the  purpose,  called  an  absorptiometer, 
consists  of  a  graduated  tube  closed  at  the  top,  and  containing 
mercury.  The  gas  is  first  introduced  into  this  tube  above  the 
mercury,  and  afterwards  the  absorbing  liquid.  This  tube  is 
enclosed  within  a  wider  one,  the  space  between  the  two  being 
filled  with  water,  by  means  of  which  any  required  tempera- 
ture may  be  imparted  to  the  contents  of  the  inner  tube.  The 
outer  tube  is  closed  at  top  with  a  lid,  in  the  middle  of  which 
is  an  elastic  cushion  pressing  firmly  on  the  inner  tube  con- 
taining the  gas.  This  tube,  by  a  peculiar  contrivance,  may 
be  either  firmly  closed  at  the  bottom,  or  made  to  communicate 
with  the  mercury  in  the  cistern  in  which  it  stands.  The 
tubes    being   filled   and   firmly  closed  top  and  bottom,  the 


648  ABSORPTION   OF   GASES. 

whole  is  vigorously  shaken  for  about  a  minute,  to  bring 
the  gas  well  in  contact  with  the  liquid.  The  inner  tube  is 
then  loosened  at  the  bottom,  so  as  to  open  a  communication 
with  the  mercury  in  the  cistern,  and  equalise  the  pressure* 
More  gas  is  then  introduced,  and  the  shaking  repeated,  and 
these  operations  are  continued,  till  the  mercury  in  the  inner 
tube  no  longer  exhibits  any  alteration  of  level.  The  volume 
of  the  remaining  gas  is  then  read  off,  and  observations  made 
of  the  pressure  and  temperature. 

The  volume  of  a  gas,  reduced  to  0°  C,  and  760  mm.  pres- 
sure, which  is  absorbed  by  the  unit  of  volume  of  any  liquid,  is 
called  the  coefficient  of  absorption.  The  formula  used  by 
Bunsen  for  calculating  these  coefficients  is  founded  on  the 
law  of  gas-absorption  discovered  by  Dr.  Henry,  viz.  that  at 
any  given  temperature,  the  weight  of  a  gas  absorbed  by  a 
given  quantity  of  a  liquid  is  proportional  to  the  pressure; 
or,  in  other  words,  that  the  volume  of  the  gas  absorbed  at 
any  given  temperature  is  the  same  under  all  pressures  (I.  75). 
Bunsen  finds,  indeed,  that  the  coefficient  of  absorption  of 
any  gas  thus  determined  under  different  pressures,  exhibits  a 
constant  value,  a  result  which  affords  a  striking  confirmation 
of  the  truth  of  Henry's  law. 

If  V  and  P  denote  the  volumes  of  a  gas  reduced  to 
0°,  before  and  after  absorption,  F  and  P'  the  corresponding 
pressures,    the   quantity    of  gas   absorbed   under  the   pres- 

V  F         F  F\ 

sure   P'  is  ^  ^^^^  —    ^  ^n^^      To  reduce  this  to  the  normal 

pressure,  0*760  mm.,  it  must  be  multiplied  by  —p?-  ;  and 
if  the  volume  of  the  absorbing  liquid  is  A,  the  coefficient  of 
absorption  a,  or  the  quantity  of  gas  absorbed  by  a  unit 
volume  of  the  liquid,  will  be 

The  following, table  exhibits  the  coefficients  of  absorption 
of  certain  gases  by  water  and  alcohol  for  every  5  degrees 
centigrade  of  temperature  : — 


COEFFICIENTS   OF   ABSORPTION. 


649 


Oxygen. 

Hydrogen. 

Nitrogen. 

Nitrous  Oxide. 

In 

In 

In 

In 

In 

In 

In 

In 

O^C. 

Water. 

Alcohol. 

Water. 

Alcohol. 

Water. 

Alcohol. 

Water. 

Alcohol. 

0-04114 

0-06925 

0-02035 

0-12634 

1-3052 

4-1780 

5 

0-03628 

0-06853 

0-01794 

0-12440 

1-0954 

3-8442 

10 

0-03250 

0-28397 

0-0193- 

0-06786 

0-01607 

0-12276 

0-9196 

3-5408 

15 

0-02989 

0-06725 

001478 

0-12142 

0-7778 

3-2678 

20 

0-02838 

0-06668 

0-01403 

0-12038 

0-6700 

3-0253 

25 

? 

006616 

• 

0-11964 

0-5962 

2-8133 

Carbonic  Oxide. 

Carbonic  Acid. 

Marsh  Gas. 

Olefiant  Gas. 

In 

In 

In 

In 

In 

In 

In 

In 

ooc. 

Water. 

Alcohol. 

Water. 

Alcohol. 

Water. 

Alcohol. 

Water. 

Alcohol. 

0-03287 

^ 

1-7967 

4-3295 

0-05449 

0-52259 

0-2563 

3-5950 

5 

0-02920 

1-4497 

3-8908 

0-04885 

0-50861 

0-2153 

33234 

10 

0-02635 

-0-20443 

1-1847 

3-5140 

0-04372 

0-49535 

0-1837 

3-0859 

15 

0-02432 

1-0020 

3-1993 

0-03909 

0-48280 

0-1615 

2-8825 

20 

0-02312 

0-9014 

2-9465 

0-03499 

0-47096 

01488 

2-7131 

25 

• 

• 

2-7558 

• 

0-1.5982 

• 

2-5778 

Sulphurc 

us  Acid. 

Hydrosulphuric  Acid. 

Chlorine. 

Nitric  Oxide. 

Ammonia. 

In 

In 

In 

In 

In 

In 

In 

0°C. 

Water. 

Alcohol. 

Water. 

Alcohol. 

Water. 

Alcohol. 

Water. 

79-789 

327-80 

4-3706 

17-891 

0-31606 

1049-60 

5 

67-485 

251-24 

3-9652 

14-776 

, 

0-29985 

917-90 

10 

56-647 

190-02 

3-5858 

11-992 

2-5852 

0-28609 

812-76 

15 

47  276 

144-13 

3-2326 

9-539 

2-3681 

0-27478 

727-22 

20 

39-374 

113-56 

29053 

7-415 

2-1565 

0-26592 

653-99 

25 

32-786 

98-33 

2-6041 

5-623 

1-9504 

0-25951 

585-94 

30 

27-161 

, 

2-3290 

. 

1  7499 

35 

22-489 

.            , 

2-0799 

. 

1-5550 

40 

18  766 

• 

1-8569 

• 

1-3655 

When  a  liquid  is  in  contact  with  a  mixture  of  several  gases, 
with  none  of  which  it  is  disposed  to  form  a  definite  compound, 
it  absorbs  of  each  gas  a  quantity  corresponding  to  the  pressure 
which  this  same  gas  exerts  in  the  mixture  that  remains  after 
the  absorption  is  complete.  Now,  in  any  mixture  of  gases, 
each  gas  exerts  the  same  pressure  that  it  would  if  it  alone 
filled  the  entire  space ;  and  the  pressure  of  the  entire  mixture 

Y  Y    3 


650  ABSORPTION   OF   GASES. 

is  equal  to  the  sum  of  the  pressures  of  the  separate  constituents. 
If,  for  example,  atmospheric  air,  which  in  100  volumes  con- 
tains 20-9  vols,  oxygen,  and  79*1  vols,  nitrogen,  exerts  alto- 
gether a  pressure  equal  to  that  of  760  mm.  of  mercury,  the 

20*9 
pressure  of  the  oxygen  is  equal  to  Yoo  •  ^^^  ~  158*8  mm. 

79*1 
and  that  of  the  nitrogen  is  -— -  .  760  =  601*2  mm. 

When  water  is  saturated  with  atmospheric  air,  it  takes 
up  of  each  constituent  a  quantity  determined  by  the  ex- 
isting temperature,  and  the  partial  pressure  of  each  gas. 
For  example,  at  13°  C,  and  under  a  pressure  correspond- 
ing to    760  mm.    of  mercury,  1  volume  of  water   absorbs 

0-03093   X  ^^  =  00646  vols,  of  oxygen,  measured  at  0°  C. 

and760mm.;  and  0-01530  x  ?^1^=   0-01210  vols,  nitro- 

760 

gen,  also  measured  at  the  standard  pressure  and  tempera- 
ture. Hence,  at  13°  C.  and  760  mm.,  1  vol.  water  absorbs 
0-00646  vols,  oxygen,  and  0-01210  vols,  nitrogen,  making 
together  0-01856  vols,  of  a  gaseous  mixture,  containing 
34-8  vols,  oxygen,  and  65-2  vols,  nitrogen.  Direct  analysis 
of  a  gaseous  mixture  evolved  by  boiling,  from  water  previ- 
ously saturated  with  atmospheric  air,  gave  34-73  vols,  pure 
oxygen  and  65*27  vols,  nitrogen. 

When  water  previously  saturated  with  oxygen  or  nitrogen 
is  exposed  to  the  air,  the  final  result  is  still  the  same,  the 
excess  of  either  gas  being  given  off,  and  the  oxygen  and 
nitrogen  being  ultimately  absorbed  in  the  proportions  just 
given.  If  water  containing  any  other  gas  is  exposed  to  the 
air,  the  whole  of  the  dissolved  gas  is  ultimately  eliminated, 
and  the  water  becomes  saturated  with  the  atmospheric  gases, 
in  the  same  proportion  as  if  no  other  gas  had  been  previously 
dissolved  in  it.  An  exception,  however,  occurs  when  the 
dissolved  gas  is  capable  of  forming  a  definite  compound  with 


NITROGEN.  651 

the  water,  in  which  case  portions  of  the  gas  and  the  water 
evaporate  together. 

The  general  law  above  stated  with  regard  to  the  absorption 
of  gaseous  mixtures  is  found  to  hold  good  in  mixtures  of  sul- 
phurous acid  gas  with  hydrogen  and  carbonic  acid ;  of  carbonic 
oxide  and  carbonic  acid ;  and  of  carbonic  oxide,  marsh-gas, 
and  hydrogen ;  but  not  with  a  mixture  of  equal  volumes  of 
chlorine  and  hydrogen,  or  of  chlorine  with  twice  or  four  times 
its  volume  of  carbonic  acid. 


NITROGEN. 

Preparation  of  Nitrogen  gas  (I.  323). — This  gas  may  be 
obtained  in  great  abundance,  and  perfectly  pure,  by  heating 
a  solution  of  nitrite  of  potash  with  sal-ammoniac  : 

KO  .  NO3  +  NH.Cl  =  KCl  +  4H0  +  2N. 

The  solution  of  nitrite  of  potash  is  prepared  by  passing  the 
nitrous  gas,  evolved  by  heating  1  part  of  starch  with  10  parts 
of  nitric  acid,  into  a  solution  of  caustic  potash  of  sp.  gr.  1*38, 
till  the  liquid  becomes  decidedly  acid,  and  then  adding  a 
sufficient  quantity  of  caustic  potash  to  restore  the  alkaline 
reaction.  The  solution  of  nitrite  of  potash  thus  obtained  may 
be  preserved  without  alteration.  On  mixing  this  liquid  with 
three  times  its  bulk  of  concentrated  solution  of  sal-ammoniac, 
and  heating  the  mixture  in  a  flask,  nitrogen  gas  is  given  off 
in  large  quantity  and  with  perfect  regularity.  Pure  nitrogen 
may  also  be  obtained  by  heating  a  solution  of  nitrite  of 
ammonia;  but  this  salt  is  difficult  to  prepare  (Corenwinder.*) 
Another  method  of  obtaining  nitrogen,  mixed  however  with 
chlorine,  is  to  heat  a  mixture  of  nitrate  of  ammonia  and  sal- 
ammoniac  : — 

2(NH4.N06)  +  NH4CI  =  5N  +  CI  +  12H0. 
After  the  mixture  has  been  heated  to  the  melting  point  of  the 

*  Ann,  Ch.  Phys.  [3],  xxvi.  296. 

Y  Y   4 


652  NITROGEN. 

nitrate,  the  reaction  goes  on  by  itself.     The  chlorine  may  be 
afterwards  absorbed  by  potash.    (Maumend.*) 

Nitrous  oxide  (I.  340). — This  gas  may  be  obtained  in  a 
state  of  purity  by  the  action  of  protochloride  of  tin  on  aqua- 
regia.  The  tin-salt  is  dissolved  in  hydrochloric  acid,  the 
solution  heated  over  the  water-bath,  and  crystals  or  cylin- 
drical lumps  of  nitre,  successively  dropped  into  it  through  a 
wide  tube  dipping  into  the  liquid.     (Gay-Lussac.f) 

Nitric  oxide  may  be  obtained  by  a  process  similar  to  that 
above  described  for  the  preparation  of  nitrous  oxide,  using 
however  protochloride  of  iron  instead  of  protochloride  of  tin. 
(Pelouze  and  Gay-Lussac.J) 

AnhydroiLS  nitric  acid,  NO5,  is  obtained  by  the  action  of  dry 
chlorine  on  nitrate  of  silver.  Chlorine  gas  contained  in  a 
gasometer  standing  in  sulphuric  acid,  is  made  to  pass  very 
slowly,  first  over  chloride  of  calcium,  then  over  sulphuric 
acid,  and  lastly  over  thoroughly  dried  nitrate  of  silver,  which 
is  heated,  first  to  95°  C,  and  afterwards  constantly  to  58°  or 
60°C.  The  products  of  decomposition  pass  into  a  U-tube 
cooled  to  21°  C,  in  which  a  very  volatile  liquid  (probably 
nitrous  acid)  collects,  together  with  crystals  of  anhydrous 
nitric  acid,  while  oxygen  escapes.  The  different  parts  of 
the  apparatus  must  be  connected  by  fusion,  as  the  acid 
vapours  would  quickly  corrode  caoutchouc  joints.  The  an- 
hydrous nitric  acid  crystallises  in  colourless  rhombic  prisms, 
having  angles  of  about  60°  and  120°,  and  in  hexagonal  prisms 
derived  therefrom.  It  melts  at  29°  to  30°  C,  and  boils  at 
45°  to  50°  C,  but  begins  to  decompose  near  its  boiling  point. 
It  becomes  strongly  heated  by  contact  with  water,  in  which  it 

*  Compt.  rend,  xxxiii.  401.  f  Ann.  Ch.  Pliys.  [3j,  xxiii.  229. 

X  Ann.  Ch.  Phys.  [3],  216. 


ESTIMATION   OF   NITROGEN.  653 

dissolves  without  colouring  or  evolution  of  gas,  forming 
liydrated  nitric  acid  (H.  Deville).*  According  to  Dumas f, 
the  crystals  melt  spontaneously  when  left  to  themselves  ;  and 
on  one  occasion,  when  an  attempt  was  made  to  recrystallise 
the  fused  mass  by  immersion  in  a  freezing  mixture,  the  tube 
was  shattered  with  explosion. 

Quantitative  estimation  of  Nitrogen, — Nitrogen  is  estimated, 
either  by  collecting  it  as  a  gas  in  the  free  state  and  measuring 
its  volume,  or  by  converting  it  into  ammonia.  Most  nitrogen- 
compounds,  when  strongly  heated  with  the  hydrates  of  the  fixed 
alkalies,  give  off  the  whole  of  their  nitrogen  in  the  form  of 
ammonia.  This  reaction  is  especially  applied  to  the  estima- 
tion of  nitrogen  in  organic  compounds,  in  which  that  element 
is  united  with  carbon,  hydrogen,  &c.  The  organic  compound 
is  mixed  with  a  large  excess  of  soda-lime  —  a  mixture  of 
caustic  soda  and  quick-lime,  the  latter  being  added  to  coun- 
teract the  deliquescence  of  the  hydrate  of  soda,  —  and  heated 
to  redness  in  a  combustion-tube  (I.  373),  to  which  is  attached  a 
suitable  bulb- apparatus  containing  hydrochloric  acid.  The 
ammonia  is  thereby  absorbed,  and  is  subsequently  precipitated 
by  chloride  of  platinum,  in  the  manner  described  at  page  385 
of  this  volume.  This  method  gives  very  exact  results  ;  but 
it  is  not  applicable  to  compounds  containing  nitrogen  in  the 
form  of  nitric  acid  or  of  peroxide  of  nitrogen,  because  in  such 
compounds  the  conversion  of  the  nitrogen  into  ammonia  by 
heating  with  caustic  alkalies  is  never  complete.  For  such 
compounds,  it  is  better  to  evolve  the  nitrogen  in  the  free 
state,  and  determine  its  quantity  by  measurement.  This 
may  be  done  either  comparatively  or  absolutely. 

For  the  comparative  determination,  the  azotised  organic 
compound  is  mixed  with  oxide  of  copper,  and  heated  in  a 
combustion-tube,  the  open  end  of  which,  to  the  depth  of 
four   or   five  inches,   is  filled   with   finely  divided   metallic 

*  Ann.  Ch.  Phys.  [3],  xxviii.  241  f  Compt.  rend,  xxviii.  323. 


654:  NITROGEN. 

copper,  obtained  by  reducing  the  oxide  with  hydrogen.  By 
the  oxidising  action  of  the  oxide  of  copper,  the  carbon  of  the 
organic  compound  is  converted  into  carbonic  acid,  and  the 
nitrogen  into  nitric  oxide  and  other  oxides  of  nitrogen,  all  of 
which  are,  however,  completely  decomposed  in  passing  over 
the  red-hot  metallic  copper,  so  that  nothing  but  nitrogen  and 
carbonic  acid  pass  out.  These  gases  are  collected  over  mer- 
cury in  a  graduated  tube,  and  their  volume  measured.  The 
carbonic  acid  is  then  absorbed  by  potash,  and  the  residual 
nitrogen  also  measured.  Now  the  weights  of  equal  volumes 
of  nitrogen  and  carbonic  acid  are  to  one  another  as  14  to  22 
(I.  149),  that  is  to  say,  as  the  atomic  weights  of  N  and  COg ; 
and  each  atom  of  carbonic  acid  contains  one  atom  of  carbon. 
Consequently,  the  volumes  of  nitrogen  and  carbonic  acid  pro- 
duced by  the  combustion  of  the  organic  compound,  are  to  one 
another  as  the  numbers  of  atoms  of  nitrogen  and  carbon. 
This  method,  of  course,  implies  that  the  carbon  in  the  organic 
compound  has  been  previously  determined. 

For  the  absolute  determination  of  nitrogen,  the  same  method 
of  combustion  and  collecting  the  gas  is  adopted,  excepting 
that  a  longer  combustion-tube  is  used,  and  a  quantity  of 
bicarbonate  of  soda  is  placed  at  the  sealed  end,  sufficient  to 
occupy  about  eight  inches  of  the  tube.  The  process  is  com- 
menced by  heating  a  portion  of  this  bicarbonate  of  soda,  so  as 
to  evolve  carbonic  acid,  and  sweep  all  the  air  out  of  the  tube. 
The  substance  is  then  burned,  and  the  evolved  gases  collected 
over  mercury,  the  carbonic  acid  being  absorbed  by  strong 
potash-ley  placed  at  the  top  of  the  mercury ;  and  when  the 
combustion  is  ended,  the  remainder  of  the  bicarbonate  of  soda 
is  heated  so  as  to  evolve  more  carbonic  acid,  and  drive  all 
the  remaining  gases  out  of  the  tube.  The  volume  of  nitrogen 
collected  is  then  read  off  and  its  weight  calculated,  the  pro- 
per corrections  being  made  for  pressure  and  temperature. 
Dr.  M.  Simpson,  of  Dublin,  has  proposed  certain  modifica- 
tions both  in  this  and  in  the  comparative  method  of  estimating 


ESTIMATION   OF   NITROGEN.  655 

nitrogen,  with  the  view  of  facilitating  the  process  and  insur- 
ing greater  accuracy.  The  principal  of  these  attentions  is 
the  replacement  of  the  oxide  of  copper  by  oxide  of  mercury, 
which  gives  up  its  oxygen  more  readily,  and,  therefore, 
insures  a  more  complete  combustion,  especially  when  the 
substance  is  rich  in  carbon.* 

The  method  of  combustion  with  oxide  of  copper  and  de- 
composition of  the  oxides  of  nitrogen  by  metallic  copper,  is 
applicable  to  all  nitrogen  compounds  whatsoever.  For  the 
analysis  of  nitrates,  in  which  the  nitrogen  is  already  com- 
pletely oxidised,  the  oxide  of  copper  may  be  dispensed  with, 
the  salt  being  simply  ignited  in  a  tube,  and  the  nitrous 
vapours  passed  over  red-hot  metallic  copper.  Nitric  acid 
may  also  be  determined  by  several  other  methods.  When  it 
exists  in  the  free  state  in  aqueous  solution,  its  quantity  may 
be  determined  by  shaking  up  the  liquid  with  carbonate  of 
baryta,  till  the  nitric  acid  is  completely  neutralised,  then  fil- 
tering, evaporating  the  filtrate  to  dryness,  care  being  taken 
not  to  heat  the  residue  too  strongly,  and  weighing  the  dry 
nitrate  of  baryta  thus  obtained.  Or  the  solution  of  nitrate 
of  baryta  may  be  decomposed  by  sulphuric  acid,  the  sulphate 
of  baryta  weighed,  and  the  equivalent  quantity  of  nitric  acid 
calculated  therefrom.  If  the  solution  of  nitric  acid  is  very 
weak,  it  is  better  to  use  baryta-water  to  neutralise  it ;  then 
pass  carbonic  acid  gas  through  the  liquid  to  remove  any 
excess  of  baryta;  filter;  and  treat  the  filtered  solution  of 
nitrate  of  baryta  as  above. 

When  nitric  acid  is  combined  with  a  base,  it  may  be  libe- 
rated by  distillation  with  sulphuric  acid  (I.  346),  and  the 
distillate  treated  with  carbonate  of  baryta  or  baryta-water,  in 
the  manner  already  described.  Or  a  weighed  portion  of  the 
nitrate  may  be  decomposed  by  sulphuric  acid  in  a  platinum 
crucible,  the  residual  sulphate  ignited  and  weighed,  and  the 
quantity   of  nitric    acid   thence   determined   by  calculation. 

*  Chcm.  Soc.  Qu.  J.  vi.  289. 


(j56  nitrogen. 

This  method,  however,  is  applicable  only  when  the  sulphate 
thus  formed  can  bear  a  red-heat  without  decomposition. 

For  the  estimation  of  small  quantities  of  nitric  acid,  such 
as  exist  in  plants,  soils,  and  waters,  some  very  ingenious 
methods  have  been  invented  by  M.  G.  Yille.*  The  nitric 
acid  is  first  converted  into  binoxide  of  nitrogen  by  boiling 
the  solution  of  the  nitrate  with  protochloride  of  iron  and  free 
hydrochloric  acid : 

NO5  +  6FeCl  +  3HC1  =  NO2  +  SFe^Clg  +  3H0 ; 

and  the  nitric  oxide  then  converted  into  ammonia,  either  by 
passing  it,  mixed  with  excess  of  hydrogen,  over  spongy  pla- 
tinuni  heated  nearly  to  redness : 

NO2  + 5H  =  NH3  +  2HO; 

or  by  passing  it,  mixed  with  excess  of  hydrogen  and  hydro- 
sulphuric  acid,  over  soda-lime  heated  nearly  to  redness  : 
NO2  +  3HS  +  2CaO  =  NH3  +  CaO  .  SO3  +  CaS^. 

The  second  method  is  generally  the  more  exact  of  the  tw^o, 
the  first  giving  accurate  results  only  when  the  quantity  of 
nitrogen  to  be  determined  is  very  small.  The  ammonia  is 
absorbed  by  an  acid  of  known  strength  contained  in  a  bulb- 
apparatus,  and  its  quantity  determined  by  the  alkalimetric 
method  (I.  547);  or  it  may  be  absorbed  by  hydrochloric 
acid,  and  precipitated  by  chloride  of  platinum.  Another 
method  is  to  pass  the  nitric  oxide  over  red-hot  metallic  cop- 
per ;  but  this  method  is  not  so  exact  as  the  precedinsr.  To 
apply  these  methods  to  the  determination  of  the  quantity  of 
nitrates  in  vegetable  substances,  soils,  waters,  &c.,  the  sub- 
stance (10  to  100  grammes)  is  exhausted  with  boiling  water, 
and  the  concentrated  solution  treated  as  above. 

Professor  Way  has  also  devised  a  method  of  estimating 
small   quantities   of  nitric  acid,  especially  adapted  to  rain- 

*  Ann.  Ch.  Phys.  [3],  vi.  20. 


VALUATION   OF   NITRE.  657 

water  and  other  waters.  This  process,  which  is  a  modifica- 
tion of  Bunsen's  volumetric  method,  consists  in  heating  the 
solid  residue  obtained  by  evaporating  about  a  pint  of  the 
water  —  previously  rendered  alkaline  by  lime-water  to  pre- 
vent loss  of  nitric  acid  —  with  hydrochloric  acid  and  iodide  of 
silver,  in  an  apparatus  from  which  the  air  has  been  com- 
pletely excluded  by  a  stream  of  carbonic  acid  gas,  and  ex- 
haustion with  the  air-pump.  The  nitrates  and  the  hydrochloric 
acid  then  decompose  each  other,  with  separation  of  nitric 
oxide  and  chlorine ;  and  the  chlorine  decomposes  the  iodide 
of  silver,  liberating  iodine,  the  amount  of  which  is  afterwards 
determined  by  a  standard  solution  of  sulphurous  acid  in  the 
manner  to  be  hereafter  described.  Organic  matter,  if  present 
in  the  water,  must  be  destroyed  by  adding  a  small  quantity  of 
permanganate  of  potash,  during  the  concentration  of  the  liquid. 
The  determination  of  the  quantity  of  nitric  acid  in  nitrate 
of  potash  is  a  process  of  considerable  commercial  importance, 
and  several  methods  have  been  devised  for  it.  Of  these, 
however,  there  are  only  two  in  general  use.  The  first, 
originally  introduced  by  Gossart  and  improved  by  Pelouze, 
consists  in  boiling  the  acidified  solution  of  the  nitre  with  a, 
solution  of  protochloride  of  iron  of  known  strength,  whereby 
the  protoxide  of  iron  is  converted  into  sesquioxide,  and  bin- 
oxide  of  nitrogen  is  evolved,  and  afterwards  determining  the 
unoxidised  portion  of  the  iron  by  the  method  of  Margueritte, 
with  a  standard  solution  of  permanganate  of  potash  (II.  6Q), 
According  to  Messrs.  Abel  and  Bloxam*,  this  method  does 
not  always  give  exact  results,  because  a  portion  of  the  nitre 
does  not  contribute  to  the  oxidising  action,  either  from  not 
being  completely  decomposed,  or  from  losing  a  portion  of  its 
acid  before  it  comes  in  contact  with  the  iron-salt.  The 
other  method,  introduced  by  Gay-Lussac,  consists  in  defla- 
grating the  nitre  with  one  fourth  of  its  weight  of  finely 
divided  charcoal  (lamp-black)  and  6  parts  of  common  salt, 

*  Chcm.  Soc.  Qu.  J.  ix.  97  ;  x.  107. 


658  CARBON. 

the  latter  being  added  merely  to  moderate  the  action.  The 
nitrate  of  potash  is  then  converted  into  carbonate,  the  quantity 
of  which  in  the  ignited  residue  may  be  determined  by  the 
process  of  alkalimetry  (I.  347).  This  method  is  also  variable 
in  its  results,  partly  because  a  portion  of  the  nitre  is  apt  to 
escape  decomposition,  partly  because  cyanate  of  potash  is 
formed  during  the  reaction,  and,  when  subsequently  dissolved 
in  water,  is  decomposed,  with  formation  of  carbonate  of  am- 
monia and  carbonate  of  potash  : 

C2NKO2  -f  4H0  =  KO.CO2  +  NH.O.COa. 
Hence,  the  quantity  of  alkali  to  be  neutralised  by  the  acid 
is  greater  than  it  should  be.  The  presence  of  alkaline  sul- 
phates in  the  nitre  also  introduces  an  error,  because  these 
salts  are  reduced  by  ignition  with  charcoal  to  sulphides,  which 
have  an  alkaline  reaction.  Messrs.  Abel  and  Bloxam  find  that 
these  several  sources  of  error  may  be  eliminated,  and  exact 
results  obtained,  by  using  the  charcoal  in  a  very  finely  divided 
state,  and  subsequently  heating  the  ignited  mass  with  chlorate 
of  potash,  which  completely  decomposes  the  cyanates  and 
reconverts  the  sulphides  into  sulphates.  The  best  form  of 
carbon  for  the  purpose  was  found  to  be  the  pure  finely  divided 
graphite  prepared  by  Mr.  Brodie's  process  (p.  661). 

CARBON. 

Volatility  of  carhon,  —  According  to  Despretz,  charcoal 
exposed  in  vacuo  to  the  heat  produced  by  a  Bunsen's  battery 
of  500  or  600  pairs,  disposed  in  5  or  6  series,  so  as  to  form 
100  pairs  of  5  or  6  times  the  ordinary  size,  is  volatilised,  and 
collects  on  the  sides  of  the  vessel  in  the  form  of  a  black  crys- 
talline powder;  in  a  space  filled  with  a  gas  with  which  the 
carbon  does  not  combine,  volatilisation  likewise  takes  place, 
but  more  slowly.  At  the  same  temperature,  charcoal  may 
also  be  bent,  welded,  and  fused,  every  kind  of  charcoal 
when  thus  treated  becoming  softer  the  longer  the  heat  is  con- 


CHARCOAL   AS  A   DISINFECTANT.  659 

tinued,  and  being  ultimately  converted  into  graphite.  Dia- 
mond exposed  to  the  same  temperature  is  likewise  converted 
into  graphite.* 

Charcoal  as  a  disinfectant,  — The  power  which  wood-char- 
coal possesses  of  absorbing  and  decomposing  gaseous  bodies 
has  lately  been  applied  by  Dr.  Stenhouse  to  the  construction 
of  ventilators  and  respirators  for  purifying  infected  atmo- 
spheres. In  a  pamphlet,  bearing  the  title  "  On  Charcoal  as  a 
Disinfectant,"  Dr.  Stenhouse  observes  —  "  Charcoal  not  only 
absorbs  effluvia  and  gaseous  bodies,  but,  especially,  when  in 
contact  with  atmospheric  air,  rapidly  oxidises  and  destroys 
many  of  the  easily  alterable  ones,  by  resolving  them  into  the 
simplest  combinations  they  are  capable  of  forming,  which  are 

chiefly  water  and  carbonic  acid Effluvia  and 

miasmata  are  generally  regarded  as  highly  organised,  nitro- 
genous, easily  alterable  bodies.  When  these  are  absorbed 
by  charcoal,  they  come  in  contact  with  highly  condensed 
oxygen  gas,  which  exists  within  the  pores  of  all  charcoal 
which  has  been  exposed  to  the  air,  even  for  a  few  minutes ; 
in  this  way  they  are  oxidised  and  destroyed."  On  this  prin- 
ciple. Dr.  Stenhouse  has  constructed  ventilators,  consisting  of 
a  layer  of  charcoal  enclosed  between  two  sheets  of  wure 
gauze,  to  purify  the  foul  air  which  accumulates  in  water- 
closets,  the  wards  of  hospitals,  and  in  the  back  courts  and  lanes 
of  large  cities.  By  the  use  of  these  ventilators,  pure  air  may 
be  obtained  from  exceedingly  impure  sources,  the  impurities 
being  absorbed  and  retained  by  the  charcoal,  while  a  current 
of  pure  air  alone  is  admitted  into  the  neighbouring  apart- 
ments. A  similar  contrivance  might  also  be  applied  to  the 
gully-holes  of  our  common  sewers,  and  to  the  sinks  in  pri- 
vate houses.  Dr.  Stenhouse  has  also  constructed  respirators, 
consisting  of  a  layer  of  charcoal  a  quarter  of  an  inch  thick, 
interposed  between  two  sheets  of  silvered  wire  gauze,  covered 
with  woollen  cloth.    They  are  made  either  to  cover  the  mouth 

^  *  Compt.  rend,  xxviii.  755. 


660  CARBON. 

and  nose,  or  the  mouth  alone ;  the  former  kind  of  respirator 
affords  an  effectual  protection  against  malaria  and  the  delete- 
rious gases  which  accumulate  in  chemical  works,  common 
sewers,  &c.  The  latter  will  answer  the  same  purpose  when 
the  atmosphere  is  not  very  impure,  provided  the  simple  pre- 
caution be  taken  of  inspiring  the  air  by  the  mouth,  and 
expiring  by  the  nose.  This  form  of  respirator  may  also  be 
useful  to  persons  affected  with  fetid  breath.  Freshly  heated 
wood-charcoal  simply  placed  in  a  thin  layer  in  trays,  and 
disposed  about  infected  apartments,  such  as  the  wards  of 
hospitals,  is  also  highly  efficacious  in  absorbing  the  noxious 
matter. 

Platinised  charcoal,  —  The  power  of  charcoal  in  inducing 
chemical  combination  is  greatly  increased  by  combination  with 
minutely  divided  platinum.  In  this  manner,  a  combination 
may  be  produced  possessing  the  absorbent  power  of  charcoal 
(which  is  much  greater  than  that  of  spongy  platinum), 
and  nearly  equal,  as  a  promoter  of  chemical  combination, 
to  spongy  platinum  itself.  In  order  to  platinise  charcoal, 
nothing  more  is  necessary  than  to  boil  it,  either  in  coarse 
powder  or  in  large  pieces,  in  a  solution  of  bichloride  of  pla- 
tinum, and,  when  thoroughly  impregnated,  which  seldom  re- 
quires more  than  ten  minutes  or  a  quarter  of  an  hour,  to  heat 
it  to  redness  in  a  close  vessel,  a  capacious  platinum  crucible 
being  well  adapted  for  the  purpose.  Charcoal  thus  platinised, 
and  containing  3  grains  of  platinum  in  50  grains  of  charcoal, 
causes  oxygen  and  hydrogen  gases  to  unite  completely  in  a 
few  minutes  ;  with  a  larger  proportion  of  platinum,  the  gases 
combine  with  explosive  violence,  just  as  if  platinum-black 
were  used.  Cold  platinised  charcoal,  held  in  a  jet  of  hydro- 
gen, speedily  becomes  incandescent,  and  inflames  the  gas. 
Platinised  charcoal,  slightly  warmed,  rapidly  becomes  incan- 
descent in  a  current  of  coal  gas ;  but  does  not  inflame  the  gas, 
owing  to  the  very  high  temperature  required  for  that  purpose. 
In  the  vapour  of  alcohol  or  wood-spirit,  platinised  charcoal 


GRAPHITE.  661 

becomes  red-hot,  and  continues  so  till  the  supply  of  vapour  is 
exhausted.  Spirit  of  wine,  in  contact  with  platinised  charcoal 
and  air,  is  converted  in  a  few  hours  into  vinegar.  Two  per 
cent,  of  platinum  is  sufficient  to  platinise  charcoal  for  most 
purposes.  Charcoal  containing  this  amount  of  platinum  causes 
oxygen  and  hydrogen  to  combine  perfectly  in  about  a  quarter 
of  an  hour,  and  such  is  the  strength  of  platinised  charcoal 
which  seems  best  adapted  for  disinfectant  respirators.  Char- 
coal containing  only  one  per  cent,  of  platinum  causes  oxygen 
and  hydrogen  to  combine  in  about  two  hours ;  and  charcoal 
containing  the  extremely  small  amount  of  ^  per  cent,  of 
platinum  produces  the  same  effect  in  six  or  eight  hours. 
Platinised  charcoal  seems  likely  to  admit  of  various  useful 
applications  ;  one  of  the  most  obvious  of  these  is  its  excellent 
adaptability  to  air-filters  and  respirators.  From  its  powerful 
oxidising  properties,  it  may  also  prove  a  highly  useful  applica- 
tion to  malignant  ulcers  and  similar  sores,  on  which  it  will  act 
as  a  mild  but  effective  caustic.  It  will  probably  also  be  found 
very  useful  in  Bunsen's  carbon  battery  (Stenhouse*). 

Graphite. — This  substance  may  be  obtained  in  the  pure  and 
finely  divided  state  by  mixing  it  in  coarse  powder  with  ^th 
of  its  weight  of  chlorate  of  potash,  adding  the  mixture  to  a 
quantity  of  strong  sulphuric  acid  equal  to  twice  the  weight  of 
the  graphite  ;  heating  the  mixture  in  the  water-bath  as  long 
as  vapours  of  peroxide  of  chlorine  are  emitted  ;  washing  the 
cooled  mass  with  water,  and  igniting  the  dry  residue  :  it  then 
swells  up  and  leaves  finely  divided  graphite.  A  chemical 
compound  of  sulphuric  acid  with  a  peculiar  oxide  of  carbon 
appears  to  be  formed  during  the  process.  If  the  graphite 
to  be  purified  contains  silicious  matters,  a  small  quantity  of 
fluoride  of  sodium  must  be  added  to  the  mixture  before 
heating  (Brodief). 

*  Chem.  Soc.  Qu.  J.  viii.  105. 
f  Ann.  Ch.  Phjs.  [3],  xlv.  351. 
VOL.  II.  Z  Z 


662  CARBON . 

Carbonic  oxide,  —  This  gas  is  rapidly  absorbed  by  a  solution 
of  subchloride  of  copper  in  hydrochloric  acid  or  ammonia, 
and  indeed  by  the  ammoniacal  solutions  of  cuprous  salts  in 
general,  e,g,  the  sulphite.  A  definite  compound  is  probably 
formed,  containing  copper  and  carbonic  oxide  in  equal  numbers 
of  atoms,  but  no  such  compound  has  yet  been  isolated.  Ferrous 
and  stannous  salts  have  no  action  on  carbonic  oxide  (Leblanc*). 

Preparation  of  olefiant  gas  (I.  385). — The  frothing  which 
causes  so  much  inconvenience  in  the  preparation  of  this  gas  by 
the  action  of  sulphuric  acid  upon  alcohol,  may  be  completely 
prevented  by  adding  a  sufficient  quantity  of  sand  to  convert  the 
mixture  into  a  thick,  scarcely  fluid  mass.  The  decomposition 
may  then  be  carried  to  the  end  without  any  frothing,  and 
nearly  all  the  carbon  of  the  alcohol  is  obtained  in  the  form  of 
olefiant  gas.  Fifty  grammes  of  alcohol  of  the  strength  of  80 
per  cent,  yield  by  this  process  more  than  22  litres  of  gas 
(Wohlerf). 

Quantitative  estimation  of  Carbon  and  its  compounds. — The 
greater  number  of  carbon-compounds  are  of  organic  nature, 
and  contain  hydrogen  as  well  as  carbon.  Hence  these  two 
elements  are  generally  estimated  together,  the  process  con- 
sisting in  burning  the  compound  with  a  large  excess  of  oxide 
of  copper,  whereby  the  carbon  is  converted  into  carbonic  acid, 
and  the  hydrogen  into  water.  The  carbonic  acid  is  absorbed 
in  a  weighed  apparatus  containing  caustic  potash,  and  the 
excess  of  weight  after  the  absorption,  gives  the  quantity  of 
carbonic  acid  produced  by  the  combustion,  y\  of  which  is  the 
weight  of  the  carbon.  The  water  is  absorbed  in  a  weighed 
apparatus  containing  dry  chloride  of  calcium,  and  ^  of  its 
weight  gives  that  of  the  hydrogen.  The  apparatus  used  for 
the  analysis  is  described  and  delineated  at  page  373,  Vol.  I. 
For  compounds  which,  like  oxalic  acid  and  sugar,  are  easily 
burned,  the  process  of  heating  with  oxide  of  copper  affords  a 

*  Compt.  rend,  xxx,  48.  f  Ann.  Tharm.  xci.  127. 


ESTIMATION    OF    CARBON.  663 

complete  combustion  of  the  carbon,  and  gives  exact  results ; 
but  when  the  proportion  of  carbon  is  very  large,  especially 
in  fatty  substances,  which  are  not  easy  to  burn,  a  different 
method  must  be  adopted.  Such  bodies  are  either  burned  with 
chromate  of  lead,  which  at  a  red  heat  gives  off  free  oxygen ; 
or  they  are  burned  with  oxide  of  copper,  and  towards  the  end 
of  the  process,  a  stream  of  oxygen  is  passed  through  the  tube, 
either  by  placing  at  the  closed  extremity  a  quantity  of  per- 
fectly dry  chlorate  of  potash,  and  heating  this  salt,  when  the 
combustion  of  the  organic  substance  by  the  oxide  of  copper 
appears  to  be  nearly  ended,  —  or  better,  by  leaving  that  end 
of  the  tube  open  and  connecting  it  with  a  gas-holder  con- 
taining oxygen.*  In  this  manner,  the  last  traces  of  carbon 
are  effectually  burned. 

The  quantity  of  carbonic  acid  in  a  carbonate  may  be  easily 
determined  by  decomposing  the  carbonate  with  sulphuric  or 
hydrochloric  acid  in  the  apparatus  represented  at  page  16  of 
this  volume,  the  flask  being  weighed  before  and  after  the 
decomposition,  and  the  quantity  of  carbonic  acid  estimated  by 
the  decrease  of  weight  resulting  from  its  evolution. 

The  quantity  of  carbonic  acid  contained  in  an  aqueous 
solution,  a  mineral  water  for  instance,  may  also  be  determined 
by  mixing  the  solution  with  chloride  of  calcium  and  excess  of 
ammonia  and  leaving  it  for  a  day  in  a  corked  flask.  The 
precipitated  carbonate  of  lime  is  then  collected  on  a  filter, 
washed,  dried,  and  weighed. 

The  amount  of  carbonic  acid  in  a  gaseous  mixture  not  con- 
taining any  other  acid,  is  estimated  by  absorbing  the  carbonic 
acid  with  caustic  potash.  When  the  proportion  of  carbonic 
acid  in  the  mixture  is  considerable,  this  end  may  be  attained 
by  placing  the  gaseous  mixture  in  a  graduated  tube   over 


*  For  details  of  the  apparatus,  and  the  mode  of  proceeding,  see  H.  Rose 
(Handb,  d.  Analyt.  Chem.  ii.  956),  and  Gerhardt  (^Traite  de  Chimie  Organique^ 
i.  35).  A  very  convenient  apparatus  for  the  purpose  has  lately  been  introduced 
by  Dr.  llofmann, 

z  z  2 


664  CARBON. 

mercury  and  passing  up  into  it  a  small  coke  ball  containing 
a  strong  solution  of  caustic  potash ;  but  when  the  pro- 
portion is  very  small,  as  in  the  air,  this  method  is  not 
sufficiently  delicate.  Accurate  results  may,  however,  be 
obtained  by  drawing  a  considerable  quantity  of  air,  by  means 
of  an  aspirator,  through  a  series  of  potash-bulbs  (I.  373)  pre- 
viously weighed,  the  quantity  of  air  drawn  through  being  of 
course  carefully  measured.  Another  method  has  recently 
been  proposed  by  Dr.  Pettenkofer ;  it  consists  in  shaking  up 
a  quantity  of  the  air  in  a  closed  vessel  of  known  capacity, 
with  an  excess  of  lime-water  of  known  strength,  and  then 
determining  the  quantity  of  lime  remaining  uncombined  by 
means  of  a  standard  solution  of  oxalic  acid.  This  method  is 
very  easy  of  execution,  and  gives  the  means  of  quickly  de- 
termining the  varying  amount  of  carbonic  acid  in  the  several 
parts  of  an  inhabited  apartment  at  different  times. 

Carbonic  oxide  is  most  readily  estimated  and  removed  from 
a  gaseous  mixture  by  means  of  a  solution  of  dichloride  of  cop- 
per (p.  97)  in  hydrochloric  acid,  which  absorbs  it  as  quickly 
and  completely  as  potash  absorbs  carbonic  acid.  When  no 
other  gaseous  compound  of  carbon  is  present,  the  quantity 
of  this  gas  may  also  be  determined  by  exploding  it  with 
oxygen,  and  absorbing  the  resulting  carbonic  acid  by  potash. 
For,  since  carbonic  acid  contains  its  own  volume  of  oxygen, 
and  carbonic  oxide  contains  half  its  volume  of  oxygen,  it 
follows,  that  if  carbonic  oxide  be  exploded  with  half  its  volume 
of  oxygen,  the  volume  of  carbonic  acid  produced  will  be 
equal  to  that  of  the  carbonic  oxide  consumed  :  hence  the 
volume  of  carbonic  oxide  is  equal  to  that  of  the  gas  which 
disappears  by  absorption  with  potash. 

The  quantity  of  marsh  gas  or  olefiant  gas  in  a  gaseous  mix- 
ture, not  containing  any  other  carbon  compound,  may  be  de- 
termined in  a  similar  manner.  Four  volumes  of  marsh  gas, 
CgH^,  require  for  complete  combustion  8  volumes  of  oxygen, 
and  produce  4  volumes  of  carbonic  acid.  For  the  2  atoms  of 
carbon  require  4  atoms  of  oxygen,  to  convert  them  into  car- 


ESTIMATION   OF   OXALIC    ACID.  665 

bonic  acid ;  and  the  4  atoms  hydrogen  require  4  atoms  oxy- 
gen to  convert  them  into  water;  therefore,  in  all,  8  atoms  or 
8  volumes  (I.  149)  of  oxygen :  moreover,  the  4  volumes  of 
oxygen  required  to  consume  the  carbon  produce  4  volumes  of 
carbonic  acid ;  hence  the  volume  of  gas  which  disappears  by 
absorption  with  potash  is  equal  to  the  original  volume  of  the 
marsh  gas. 

By  a  similar  calculation,  it  is  found  that  4  volumes  of 
olefiant  gas,  C^H^,  require  12  volumes  of  oxygen  for  com- 
plete combustion,  and  produce  8  volumes  of  carbonic  acid : 
hence  the  volume  of  olefiant  gas  is  equal  to  half  the  volume 
of  gas  removed  by  potash  after  the  explosion.  Olefiant  gas 
may  also  be  removed  from  a  gaseous  mixture  by  the  introduc- 
tion of  a  coke-ball  saturated  with  anhydrous  sulphuric  acid 
or  fuming  oil  of  vitriol  (p.  564). 

For  the  methods  of  analysing  gaseous  mixtures  containing 
marsh  gas  and  olefiant  gas  mixed  with  hydrogen,  carbonic 
oxide,  nitrogen,  and  other  gases,  I  must  refer  to  works  in  which 
the  operations  of  gas-analysis  are  explained  in  detail.* 

Oxalic  acid  is  precipitated  from  its  aqueous  solution,  or 
from  solutions  of  the  alkaline  oxalates,  by  chloride  of  calcium, 
ammonia  being  added  if  necessary  to  render  the  solution 
neutral.  The  precipitated  oxalate  of  lime  is  converted  by 
ignition  at  a  low  red  heat  into  carbonate,  from  the  weight  of 
which  the  quantity  of  oxalic  acid  may  be  calculated,  each 
atom  of  carbonate  of  lime  (CaO  .  COg)  corresponding  to 
1  atom  of  anhydrous  oxalic  acid,  Cfi^ :  — 

CaO.CA    =    CaO.CO^    +    CO. 

Oxalate  of  lime.  Carbonate  of 

lime. 

Consequently,  50  parts  of  carbonate  of  lime  give  36  parts  of 
anhydrous  oxalic  acid,  Cfi^,  or  45  parts  of  the  hydrated  acid, 
C2HO4.     In  neutralising  the  solution  of  an  acid  oxalate  with 

*  Bunsen's  "  Gasometry,"  translated  by  Eoscoe,  London,  1857 ;  and  Regnault, 
"  Com-s  Elementaire  de  Chimie,"  2me.  ed.  Paris,  torn.  iv.  pp.  73-103. 

z  z  3 


666  CARBON. 

ammonia^  care  must  be  taken  to  avoid  excess  of  the  alkali, 
as  in  that  case  carbonic  acid  will  be  absorbed  from  the  air,  and 
carbonate  of  lime  will  be  precipitated  as  well  as  oxalate.  It 
is  better,  however,  to  precipitate  oxalic  acid  from  its  acid 
solutions  with  acetate  of  lime,  as  oxalate  of  lime  is  quite 
insoluble  in  acetic  acid. 

Oxalic  acid  may  also  be  very  exactly  estimated  by  means 
of  a  solution  of  terchloride  of  gold.  The  gold  is  then  re- 
duced to  the  metallic  state,  water  is  decomposed,  and  the 
liberated  oxygen  converts  the  oxalic  acid  into  carbonic  acid :  — 

3C2O3  +  AuClg  +  3H0  =  6CO2  +  3HC1  +  Au. 

The  decomposition  may  be  performed  in  the  flask  apparatus 
already  referred  to  (fig.  1,  p.  16).  It  takes  place  at  ordinary 
temperatures,  but  the  liquid  must  be  boiled  at  the  end  of  the 
process  to  expel  the  last  portions  of  carbonic  acid.  This 
method  may  be  applied  to  the  decomposition  of  all  oxalates, 
whether  soluble  or  insoluble  in  water,  the  insoluble  oxalates 
being  dissolved  in  hydrochloric  acid.  An  excess  of  that  acid 
in  the  concentrated  state,  however,  greatly  interferes  with  the 
action ;  the  liquid  should,  therefore,  be  considerably  diluted 
with  water,  and  the  action  assisted  by  heat.  The  preceding 
equation  shows  that  2  atoms  carbonic  acid,  COg,  correspond 
to  1  atom  of  anhydrous  oxalic  acid,  CgOg,  or  11  parts  by 
weight  of  carbonic  acid  to  9  parts  of  anhydrous  oxalic  acid. 

Another  mode  of  converting  oxalic  acid  into  carbonic  acid, 
is  by  acting  upon  it,  either  in  the  free  or  combined  state, 
with  binoxide  of  manganese  and  sulphuric  or  hydrochloric 
acid  (p.  16). 

Oxalic  acid,  either  free  or  combined,  is  resolved,  by  heating 
with  an  excess  of  strong  sulphuric  acid,  into  a  mixture  of 
equal  volumes  of  carbonic  acid  and  carbonic  oxide.  This 
method  may  also  be  applied  to  the  estimation  of  oxalic  acid, 
but  it  is  not  so  accurate  as  the  preceding. 

Lastly,  the  quantity  of  oxalic  acid  in  an  oxalate  may  be  esti- 
mated by  burning  the  compound  with  oxide  of  copper  (p.  662). 


BORON.  667 

Estimation  of  Cyanogen, — The  quantity  of  cyanogen  in  a 
soluble  cyanide  is  easily  determined  by  precipitation  with 
nitrate  of  silver.  The  precipitated  cyanide  of  silver  is  col- 
lected on  a  weighed  filter  and  dried  at  100°  C.  Every  134 
parts  of  it  contain  26  parts  of  cyanogen.  Many  insoluble 
cyanides  may  be  decomposed  by  boiling  with  sulphuric  or  hy- 
drochloric acid,  hydrocyanic  acid  being  evolved,  and  the 
metal  remaining  as  sulphate  or  chloride,  from  the  weight  of 
which  the  quantity  of  cyanogen  which  has  gone  off  may  be 
calculated.  Lastly,  all  cyanogen  compounds  whatever  may 
be  analysed  by  burning  with  oxide  of  copper,  in  the  manner 
already  described. 

BORON. 

This  element  was  formerly  known  only  in  the  amorphous 
state,  in  which  it  is  obtained  by  the  action  of  potassium  on 
boracic  acid  or  borofluoride  of  potassium.  But  Wohler  and 
Deville*  have  lately  obtained  it  in  two  distinct  crystalline 
states,  in  one  of  which  it  bears  a  close  resemblance  to  diamond, 
and  in  the  other  to  graphite. 

The  first  of  these  crystalline  forms  of  boron  is  obtained  by 
decomposing  boracic  acid  with  aluminium  at  a  high  temper- 
ature. When  80  grammes  of  aluminium  in  thick  lumps,  and 
100  grammes  of  fused  or  pulverised  boracic  acid,  are  heated 
together  in  a  crucible  lined  with  charcoal  to  about  the  melting 
point  of  nickel  for  five  hours,  there  are  found  on  breaking 
the  crucible  after  cooling,  two  distinct  layers,  one  of  which  is 
glassy,  and  consists  of  boracic  acid  and  alumina,  while  the 
other  is  metallic,  tumefied,  has  an  iron-grey  lustre,  and  consists 
of  aluminium  mixed  with  a  considerable  quantity  of  crystal- 
lised boron,  some  of  the  crystals  being  distinctly  visible  at  the 
surface.  The  aluminium  is  dissolved  out  by  strong  boiling 
soda-ley,  and  the  residual  boron  is  freed  from  iron  by  digestion 

*  Compt.  rend."  xliii.  1088. 
z  z  4 


668  BOROX. 

in  hydrochloric  acid,  and  from  traces  of  silicon  by  a  mixture 
of  nitric  and  hydrofluoric  acids.  It  is  still,  however,  mixed 
with  laminae  of  alumina,  which  must  be  carefully  picked  out. 

The  pure  product  thus  obtained  is  diamond-boron,  mixed, 
however,  with  a  small  quantity  of  graphitoidal  boron,  which 
latter  being  very  light,  may  be  removed  by  suspension  in  water. 
Diamond-boron  forms  transparent  crystals,  having  a  honey- 
yellow  or  garnet-red  colour,  due  to  the  presence  of  small 
quantities  of  foreign  substances  ;  it  has  hitherto  been  ob- 
tained only  in  confused  aggregates  of  small  crystals.  In 
lustre  and  refractive  power,  it  is  scarcely  inferior  to  the 
diamond ;  and  is  one  of  the  hardest  bodies  known,  inasmuch 
as  it  scratches  corundum,  and  even  the  diamond  itself.  It 
does  not  fuse  at  the  heat  of  the  oxyhydrogen  blowpipe,  and 
withstands  the  action  of  oxj^gen  even  when  strongly  heated ; 
but  it  is  slightly  oxidised  at  the  temperature  at  which  the 
diamond  burns,  a  film  of  boracic  acid  being  then  formed, 
which  protects  the  remainder  of  the  crystals  from  oxidation. 
Heated  to  redness  in  chlorine  gas,  it  burns  and  produces 
chloride  of  boron.  Heated  by  the  blowpipe  between  two 
pieces  of  platinum-foil,  it  forms  a  fusible  boride  of  platinum. 
It  is  not  attacked  by  acids  at  any  temperature,  but  when 
heated  to  redness  with  bisulphate  of  potash,  it  is  converted 
into  boracic  acid.  It  is  not  attacked  by  a  strong  boiling  so- 
lution of  caustic  soda ;  but  hydrate  and  carbonate  of  soda 
dissolve  it  slowly  at  a  red  heat.  Nitre  does  not  appear  to  act 
upon  it  sensibly  at  that  temperature. 

Graphitoidal  Boron  is  produced  in  small  quantity  simul- 
taneously with  diamond-boron  by  the  process  above  described. 
But  it  is  obtained  much  more  readily  by  treating  borofluo- 
ride  of  potassium  with  aluminium,  adding  as  a  flux  a  mix- 
ture of  equal  parts  of  chloride  of  potassium  and  chloride 
of  sodium ;  in  this  manner,  small  masses  of  boride  of  alu- 
minium are  obtained,  which,  when  digested  in  hydrochloric 
acid,  leave  graphitoidal  boron.    The  laminaB  of  this  substance 


BORACIC   ACID.  669 

are  often  hexagonal :  they  have  a  slight  reddish  colour,  and  the 
form  and  lustre  of  native  graphite.  They  are  always  opaque. 
Amorphous  boron  is  formed  in  the  preparation  of  diamond - 
boron  when  a  small  globule  of  aluminium  comes  in  contact 
with  a  large  quantity  of  boracic  acid,  so  that  the  boron  does 
not  dissolve  in  the  aluminium  as  fast  as  it  is  set  free.  In  this 
case,  after  the  aluminium  has  been  removed  by  the  use  of 
caustic  soda  and  hydrochloric  acid,  the  boron  remains  as  an 
amorphous  mass  of  a  light  chocolate  colour,  and  exhibiting 
the  properties  which  have  long  been  known  as  belonging  to 
boron.  When  the  amorphous  boron  is  collected  on  a  filter, 
the  portion  which  remains  adhering  to  the  filter,  burns,  when 
the  paper  is  dried  and  set  on  fire,  very  easily  and  with  an 
intense  light;  graphitoidal  boron,  under  the  same  circum- 
stances, does  not  burn  at  all. 

Boracic  acid. — According  to  A.  Yogel  *,  the  brown  colour 
imparted  to  turmeric  by  boracic  acid  is  distinguished  from 
that  produced  by  alkalies,  by  not  being  destroyed  by  the 
action  of  acids.  Thus,  when  an  alcoholic  tincture  of  turme- 
ric diluted  with  water  till  its  colour  becomes  light  yellow,  is 
added  to  a  concentrated  solution  of  borax,  the  yellow  colour 
is  changed  to  brown  by  the  alkaline  reaction  of  the  salt,  but 
on  adding  a  certain  quantity  of  sulphuric  acid,  the  yellow 
colour  is  restored.  A  larger  quantity  of  sulphuric  acid  sets 
free  the  boracic  acid,  and  again  produces  a  brown  colour ; 
which,  however,  does  not  disappear  on  further  addition  of  the 
acid. 

For  detecting  small  quantities  of  boracic  acid  in  solutions, 
mineral  waters,  for  instance,  H.  Rose  f  acidulates  the  liquid 
with  hydrochloric  acid,  dips  a  strip  of  turmeric  paper  into 
the  liquid,  and  then  leaves  it  to  dry ;  if  boracic  acid  is  pre- 
sent, the  part  of  the  paper  which  has  been  immersed  in  the 
liquid,  assumes  a  red- brown  colour. 

*  Repert.  Pharm.  iii.  178.  f  Handb.  d.  Analyt.  Chem.  i.  919,  946. 


670  BORON. 

Boracic  acid  being  but  a  weak  acid,  its  salts  are  often  de- 
composed by  water.  A  concentrated  solution  of  borax, 
added  to  nitrate  of  silver,  throws  down  white  borate  of 
silver ;  but  a  dilute  solution  —  which  in  fact  consists  of  borate 
of  water  mi:^d  with  free  soda  —  forms  a  brown  precipi  tate  of 
oxide  of  silver.  If  to  a  strong  solution  of  borax,  an  alcoholic 
tincture  of  litmus  reddened  by  acetic  acid  be  added  in  such 
quantity  that  the  red  colour  is  nearly  but  not  quite  destroyed, 
and  the  liquid  be  then  diluted  with  water,  the  red  colour  is 
immediately  changed  to  blue  (H.  Rose*). 

Nitride  of  Boron,  BN. — This  compound  was  discovered 
by  Balmain  f,  who  at  first  regarded  it  as  capable  of  uniting 
with  metals  and  forming  compounds  analogous  to  the  cyanides, 
but  afterwards  found  that  all  these  supposed  metallic  com- 
pounds were  one  and  the  same  substance,  viz.  nitride  of  boron, 
without  any  appreciable  amount  of  metal.  Balmain  obtained 
this  substance  by  heating  boracic  acid  with  cyanide  of  potas- 
sium or  cyanide  of  zinc,  or  with  cyanide  of  mercury  and 
sulphur.  It  has  since  been  more  completely  investigated  by 
Wohler  J,  who  prepares  it  by  heating  to  bright  redness,  in  a 
porcelain  or  platinum  crucible,  a  mixture  of  2  pts.  of  dried 
sal-ammoniac  and  1  pt.  of  pure  anhydrous  borax.  The  pro- 
duct is  a  white  porous  mass,  which  is  pulverised  and  washed 
with  water  to  free  it  from  chloride  of  sodium.  The  final 
washings  must  be  made  with  boiling-water  acidulated  v»'ith 
hydrochloric  acid.  Boracic  acid  may  be  used  in  the  prepara- 
tion instead  of  borax.  Wohler  formerly  obtained  the  nitride 
of  boron  by  igniting  anhydrous  borax  with  ferrocyanide  of 
potassium. 

Nitride  of  boron  is  a  white  amorphous  powder,  tasteless, 
inodorous,  soft  to  the  touch,  insoluble  in  water,  infusible,  and 
non-volatile.     Heated  at  the  point  of  the  blowpipe-flame,  it 

*  Ann.  Ch.  Pharm,  Ixxxiv.  216. 

t  Phil.  Mag.  [3].  xxi.  170;  xxii.  467;  xxiil.  71;  xxiv.  191. 

:j:  Ann.  Ch.  Pharm.  Ixxiv.  70. 


ESTIMATION   OF    BORON.  671 

burns  with  a  bright  greenish-white  flame.  It  easily  reduces 
the  oxides  of  copper  and  lead,  giving  off  nitrous  fumes. 
Heated  in  a  current  of  aqueous  vapour,  it  yields  ammonia 
and  boracid  acid :  — 

BN  +  3H0  =  BO3  +  NH3. 

Alkalies,  and  the  greater  number  of  acids,  even  in  the  state 
of  concentrated  solution,  have  no  action  on  nitride  of  boron ; 
strong  sulphuric  acid,  however,  with  the  aid  of  heat,  ulti- 
mately converts  it  into  ammonia  and  boracic  acid.  Fuming 
hydrofluoric  acid  converts  it  into  borofluoride  of  ammonium. 
Nitride  of  boron  undergoes  no  alteration  when  heated  in  a 
current  of  chlorine.  When  fused  with  hydrate  of  potash,  it 
gives  off  a  large  quantity  of  ammonia.  With  anhydrous 
carbonate  of  potash,  it  yields  borate  and  cyanate  of  potash :  — 

BN  +  2(K0  .  CO2)  =  BO3 .  KO  +  C2NO.  KO. 

It  does  not  decompose  carbonic  acid,  even  at  the  highest 
temperatures.  Marignac  *  found  also  that  nitride  of  boron 
does  not  form  definite  compounds  with  metals,  and  that  its 
formula  is  BN. 

Estimation  of  Boron  and  Boracic  acid,  —  The  most  exact 
method  of  estimating  boron  is  to  convert  it  into  borofluoride 
of  potassium,  KF  .  BF3.  If  the  substance  to  be  treated  is 
free  boracic  acid  or  an  alkaline  borate,  a  sufficient  quantity 
of  potash  is  first  added,  then  an  excess  of  pure  hydrofluoric 
acid  (so  that  the  escaping  vapours  may  redden  litmus),  and 
the  mixture  is  evaporated  to  dryness  in  a  silver  or  platinum 
vessel.  The  dry  saline  mass  is  then  stirred  up  with  a  solu- 
tion of  acetate  of  potash  containing  20  per  cent,  of  the  salt ; 
then,  after  a  few  hours,  thrown  on  a  weighed  filter,  and  the 
precipitate  washed,  first  with  the  solution  of  acetate  of  potash, 
till  the  filtrate  no  longer  gives  a  precipitate  with  chloride 
of  calcium,  then    with  strong  alcohol,   and    dried  at   100°. 

*  Ann.  Cli.  Phann.  Ixxix.  247. 


672  SILICON. 

The  residue  consists  of  borofluoride  of  potassium,  every  124*7 
parts  of  which  correspond  to  34*9  of  boracic  acid  and  10*9  of 
boron. 

The  twenty  per  cent,  solution  of  acetate  of  potash  dissolves 
chloride  of  potassium  and  phosphate  of  potash,  and  likewise 
the  sulphate,  though  less  readily ;  it  also  dissolves  soda-salts ; 
the  fluoride,  however,  slowly.  Any  other  bases  which  may 
be  combined  with  the  boracic  acid,  must  be  previously 
separated  by  boiling  or  fusing  the  compound  with  carbonate 
of  potash  (A.  Stromeyer  *). 

Boracic  acid  cannot  be  estimated  in  its  aqueous  solution  by 
simple  evaporation  to  dryness,  since  a  large  quantity  of  it 
goes  oflp  with  the  watery  vapour. 


SILICON. 

Silicon,  like  boron,  may  be  obtained  in  three  states  analo- 
gous to  the  amorphous,  graphitoidal,  and  diamond  forms  of 
carbon.  The  amorphous  variety  is  that  which  Berzelius  ob- 
tained by  the  action  of  potassium  on  silicofluoride  of  potassium 
(I.  391).  H.  Ste-Claire  Devillef  prepares  amorphous  silicon 
by  passing  the  vapour  of  the  chloride  over  red-hot  sodium  in 
an  atmosphere  of  dry  hydrogen.  The  silicon  thus  obtained 
exhibits,  after  washing  and  drying  at  a  moderate  heat,  the 
properties  described  by  Berzelius. 

Silicon  is  fusible  —  its  melting  point  being  intermediate 
between  the  melting  points  of  steel  and  cast-iron ;  but  when 
heated  in  the  air,  it  quickly  becomes  encrusted  with  a  coating 
of  silicic  acid,  which  being  exceedingly  difficult  of  fusion, 
causes  the  silicon  also  to  appear  infusible. 

Graphitoidal  Silicon. — This  modification  of  silicon  was  first 
obtained  by  Deville  in  preparing  aluminium  by  the  electro- 

*  Ann.  Ch.  Pharm.  c.  82. 

t  Ann.  Chem.  Phys.  [3],  xlix.  G2. 


SILICON.  673 

lysis  of  the  double  chloride  of  aluminium  and  sodium.  The 
first  portions  of  aluminium  thus  obtained  are  contaminated 
with  silicon  derived  from  the  charcoal  electrodes ;  and  when 
this  alloy  of  silicon  and  aluminium  is  treated  with  hydro- 
chloric acid,  the  silicon  remains  undissolved  in  the  form  of 
shining  metallic  scales  resembling  graphite.  A  more  pro- 
ductive method  of  obtaining  this  variety  of  silicon  is  given 
by  Wohler.  *  It  consists  in  mixing  aluminium  with  between 
20  and  40  times  its  weight  of  silico-fluoride  of  potassium, 
and  heating  the  mixture  in  a  Hessian  crucible  to  the  melting 
point  of  silver.  A  metallic  button  is  thus  obtained,  which, 
when  treated  successively  with  hydrochloric  and  hydrofluoric 
acids,  yields  graphitoidal  silicon,  partly  in  isolated  hexagonal 
tables,  the  edges  of  which  are  often  curved.  This  graphitoi- 
dal silicon  exhibits  all  the  properties  ascribed  by  Berzelius  to 
silicon  which  has  been  strongly  heated.  Its  density  is  2*49, 
which  is  less  than  that  of  quartz  (from  2*6  to  2*8).  It  may 
be  heated  to  whiteness  in  oxygen  gas  without  burning  or 
undergoing  any  alteration  in  weight;  but  when  heated  to 
redness  with  carbonate  of  potash,  it  decomposes  the  carbonic 
acid,  with  vivid  emission  of  light  and  formation  of  silica.  It 
is  not  attacked  by  any  acid.  A  strong  solution  of  potash  or 
soda  dissolves  it  slowly,  with  evolution  of  hydrogen.  Heated 
to  commencing  redness  in  dry  chlorine  gas,  it  burns  com- 
pletely, and  forms  chloride  of  silicon. 

Octohedral  or  Diamond  Silicon. — When  vapour  of  chloride 
of  silicon  is  passed  over  aluminium  kept  in  a  state  of  fusion 
in  an  atmosphere  of  hydrogen,  part  of  the  aluminium  is  con- 
verted into  chloride,  which  volatilises,  and  the  silicon  thereby 
separated  dissolves  in  the  remaining  aluminium,  which  thus 
becomes  more  and  more  saturated  with  silicon ;  and  at  length 
a  point  is  attained  at  which  the  excess  of  silicon  separates  from 
the  melted  aluminium  in  large  beautiful  needles,  having  a 
dark  iron-grey  colour,  reddish  by  reflected  light,  and  ex- 
*  Compt.  rend.  xlii.  48. 


674  SILICON. 

hibiting  iridescence  like  that  of  iron-glance.  These  crystals 
are  derived  from  the  regular  octohedron,  and  often,  like  the 
diamond,  exhibit  curved  faces ;  they  are  very  hard,  and  are 
capable  of  scratching  and  of  cutting  glass  (Deville). 

Atomic  weight  of  Silicon. — It  is  still  a  disputed  question 
whether  the  atomic  weight  of  silicon  should  be  21*35  or  14*1 
and  accordingly,  whether  the  formula  of  the  oxide,  chloride, 
&c.,  should  be  SiOg,  SiClg  &c.,  or  SiO^,  SiCl^,  &c.  The 
vapour-density  of  the  chloride,  5*939  according  to  Dumas, 
is  in  favour  of  the  formula  SiCla,  which  gives  a  condensation 
to  2  volumes  (or  rather  SigCl^  giving  a  condensation  to  4 
vols.),  whereas  the  formula  SiClg  would  involve  the  very 
unusual  condensation  to  3  volumes.  An  argument  in  favour 
of  this  latter  formula  has  been  drawn  from  the  difference  be- 
tween the  boiling  points  of  the  bromide  and  chloride  of  silicon 
(153°  —  59°C  =  94  =  3  X  32  nearly),  inasmuch  as  the 
earlier  researches  of  H.  Kopp  had  led  him  to  conclude  that 
the  boiling  points  of  analogous  chlorides  and  bromides  gene- 
rally differ  by  multiples  of  32°  C.  Kopp  has,  however,  more 
recently  shown  that  this  law  is  very  far  from  being  a  general 
expression  of  observed  results,  and  that  the  difference,  23*5° 
or  its  multiples,  occurs  quite  as  frequently.  Now  the  differ- 
ence 94  between  the  boiling  points  of  bromide  and  chloride 
of  silicon,  is  just  4  x  23*5,  and  is  therefore  so  far  consistent 
with  the  formulae  Si2Br4  and  Si2Cl4. 

Colonel  Yorke  *  has  endeavoured  to  determine  the  formula 
of  silicic  acid,  by  ascertaining  the  quantity  of  carbonic  acid 
displaced  from  excess  of  an  alkaline  carbonate  by  fusion  with 
a  given  weight  of  silica.  Experiments  with  carbonate  of 
potash  gave,  as  a  mean  result,  30*7  for  the  equivalent  of 
silicic  acid,  agreeing  with  the  formula  SiOg  (14*1  +  2x8 
=  30*1).  Experiments  with  carbonate  of  soda  gave  21*3 
for  the  equivalent  of  silicic  acid,  agreeing  nearly  with  half 
that  which  is  represented  by  the  formula    SiOg  (21*35    -h 

*  Proceedings  of  the  Royal  Society,  viii.  1 40. 


ATOMIC   WEIGHT   OF   SILICON.  675 

3x8  =  45*35).  Experiments  with  carbonate  of  lithia  gave 
the  number  14*99,  agreeing  nearly  with  the  formula  SiO. 
Bjr  fusing  23  parts  of  silica  with  54  parts  of  carbonate  of 
soda,  dissolving  the  fused  mass  in  water,  and  evaporating  the 
solution  in  vacuo,  a  crystallised  salt  was  formed  containing 
(besides  5  per  cent,  of  carbonate  of  soda)  the  salt  NaO .  SiOg 
+  7H0.  These  results  seem  to  show  that  silicon  is  capable 
of  uniting  with  oxygen  in  more  than  one  proportion,  a  con- 
clusion in  accordance  with  the  results  obtained  by  other  ex- 
perimenters. 

Wohler  and  Buff*,  by  heating  silicon  to  low  redness  in  a 
current  of  dry  hydrochloric  acid  gas,  have  obtained  a  new 
chloride  of  silicon,  which  is  a  mobile  fuming  liquid,  more 
volatile  than  the  terchloride.  Water  decomposes  this  liquid, 
forming  hydrochloric  acid,  and  a  new  oxide  of  silicon,  which 
is  a  white  substance,  slightly  soluble  in  water,  but  dissolving 
very  easily  in  alkalies,  —  even  in  ammonia,  with  evolution  of 
hydrogen  and  formation  of  silicic  acid.  When  heated  in  the 
air,  it  burns  with  a  white  flame.  This  compound  is  evidently 
a  lower  oxide  of  silicon,  but  its  exact  composition  has  not  yet 
been  determined. 

Fuchs  has  obtained  two  hydrates  of  silicic  acid ;  one  con- 
taining between  9*1  and  9*6  per  cent,  of  water,  the  other 
between  6-6  and  7  per  cent.  The  former  might  be  denoted 
by  either  of  the  formulas,  2Si03.HO  or  38102-  HO,  accord- 
ing to  the  atomic  weight  of  silicon  chosen ;  but  the  latter 
agrees  only  with  the  formula,  4Si02.HO.t 

The  true  formula  of  silicic  acid  and  atomic  weight  of  silicon 
must  then  be  considered  as  still  undecided ;  the  balance  of 
evidence  seems,  however,  to  incline  in  favour  of  the  formula 
SiOg,  making  the  atomic  weight  of  silicon  14*1.  The  analogy 
between  silicic  acid  and  titanic  acid  points  to  the  same  con- 
clusion. 

Silicmretted  Hydrogen,  —  A  remarkable  gaseous  compound 

*  Compt.  rend.  xliv.  834.  f  Ann.  Ch.  Pharm.  Ixxxii.  119. 


676  SILICON. 

of  silicon  and  hydrogen  is  produced  when  a  bar  of  aluminium 
containing  silicon  is  connected  with  the  positive  pole  of  a 
Bunsen's  battery  of  8  to  12  cells,  and  made  to  dip  into  a 
solution  of  chloride  of  sodium.  The  aluminium  then  dis- 
solves in  the  form  of  chloride,  a  considerable  quantity  of  gas 
is  evolved  at  its  surface,  and  many  of  the  gas-bubbles,  as 
they  escape  into  the  air,  take  fire  spontaneously,  burning  with 
a  white  light  and  diffusing  a  white  fume.  When  the  gas  is  col- 
lected in  a  tube  over  water,  and  bubbles  of  oxygen  are  passed 
up  into  it,  each  successive  bubble  produces  at  first  a  brilliant 
white  light  and  a  copious  white  fume  ;  but  this  effect  gradu- 
ally diminishes  in  intensity,  and  at  last  the  remaining  gas  will 
no  longer  burn  spontaneously  by  contact  with  oxygen.  This 
residual  gas  is  hydrogen  ;  the  spontaneously  inflammable  gas, 
which  forms  but  a  small  portion  of  the  mixture,  is  siliciuretted 
hydrogen.  When  the  gaseous  mixture  is  made  to  escape 
from  a  glass  jar  provided  with  a  stop-cock,  it  burns  in  a  jet, 
and  deposits  silica  round  the  orifice.  A  piece  of  white  porce- 
lain held  in  the  flame,  becomes  stained  with  a  brown  deposit 
of  silicon  ;  and  if  the  gas  be  made  to  pass  through  a  narrow 
glass  tube,  and  heated  till  the  glass  softens,  a  deposit  of  silicon 
is  likewise  obtained,  and  the  gas  which  issues  from  the  tube  is 
no  longer  spontaneously  inflammable.  The  compound  has  not 
yet  been  analysed  quantitatively. 

The  formation  of  siliciuretted  hydrogen  appears  to  be  due 
to  a  secondary  action  accompanying  the  electrolysis  of  the 
saline  solution.  The  aluminium,  forming  the  .positive  pole  of 
the  battery,  combines  with  the  chlorine  and  dissolves;  but 
the  quantity  of  aluminium  removed  is  about  one-fourth 
greater  than  that  which  is  equivalent  to  the  quantity  of 
chlorine  eliminated  from  the  solution.  This  excess  of  alumi- 
nium is  found  to  be  removed  in  the  form  of  alumina,  uniting 
with  oxygen  derived  from  the  water  of  the  solution.  The 
equivalent  quantity  of  hydrogen  is  of  course  evolved,  and 
part  of  it  enters  into  combination  with  the  silicon  contained 


ESTIMATION    OF    SILICON.  677 

in  the  aluminium.  The  compound  has  not  yet  been  obtained 
by  a  purely  chemical  reaction ;  but  it  has  been  observed 
that  the  hydrogen  evolved,  when  aluminium  dissolves  in 
hydrochloric  acid,  burns  with  a  brighter  flame  than  pure 
hydrogen,  and  yields  a  small  deposit  of  silica  (Wohler  and 
BufF*). 

Estimation  of  Silicon  and  Silicic  add,  —  When  silica  exists 
in  solution",  it  may  be  completely  separated  from  all  the  other 
substances  present,  by  acidulating  the  solution  with  hydro- 
chloric acid,  evaporating  to  dryness,  and  boiling  the  residue 
with  water  containing  hydrochloric  acid,  which  will  dissolve 
everything  excepting  the  silica.  The  residue  may  then  be 
dried,  ignited,  and  weighed.  The  completeness  of  this  sepa- 
ration depends  on  the  perfect  drying  of  the  silica  before  it  is 
boiled  with  the  acidulated  water.  Now,  to  ensure  this  com- 
plete dryness,  the  silica  must  be  heated  somewhat  above  the 
temperature  of  the  water-bath,  the  drying  being  completed 
on  a  sand-bath  or  over  a  lamp.  In  doing  this,  it  sometimes 
happens  that  too  much  heat  is  applied,  and,  in  that  case,  cer- 
tain other  substances,  especially  alumina  and  oxide  of  iron, 
may  also  be  rendered  insoluble  in  the  dilute  acid.  To  ob- 
viate this  source  of  error,  the  dried  residue  must  be  moist- 
ened all  over  with  strong  hydrochloric  acid,  then  left  to  stand 
for  half  an  hour,  and  afterwards  boiled  with  water.  Every- 
thing will  then  dissolve  excepting  the  silica. 

Analysis  of  Silicates.  —  Some  natural  silicates,  cerite,  for 
example,  are  completely  decomposed  by  hydrochloric  acid. 
In  that  case,  it  is  sufficient  to  boil  the  pulverised  mineral  with 
strong  hydrochloric  acid  as  long  as  anything  continues  to  be 
dissolved  ;  then  evaporate  to  complete  dryness,  and  treat  the 
residue  as  above.  The  liquid  filtered  from  the  insoluble 
silica  contains  the  bases  of  the  mineral,  which  may  be  sepa- 
rated and  estimated  by  methods  already  described. 

♦  Ann.  Ch.  Pharm.  ciii.  218. 
VOL.  II.  3  A 


678  SILICON. 

Silicates  which,  like  felspar,  resist  the  action  of  hydro- 
chloric acid,  are  decomposed  by  fusion  with  an  alkaline  car- 
bonate. The  mineral,  very  finely  powdered,  is  mixed  in  a 
platinum  crucible  with  three  or  four  times  its  weight  of  dry 
carbonate  of  soda ;  the  platinum  crucible,  placed  within  an 
earthen  crucible  lined  with  magnesia,  and  heated  to  bright 
redness  in  a  furnace  for  about  twenty  minutes ;  the  fused 
mass,  when  cold,  removed  from  the  crucible  by  digestion  in 
dilute  hydrochloric  acid  with  the  aid  of  heat;  the  whole 
evaporated  to  dryness ;  and  the  silica  separated,  and  the  bases 
determined  as  above.  Some  silicates,  zircon  for  example, 
resist  the  action  of  alkaline  carbonates,  and  must  be  decom- 
posed by  fusion  with  hydrate  of  potash  or  soda  in  a  silver 
crucible. 

By  this  process,  not  only  the  silica,  but  all  the  bases  of  a 
silicate  may  be  determined,  excepting  the  alkalies.  To  deter- 
mine these,  the  mineral,  reduced  to  an  almost  impalpable 
powder,  is  very  intimately  mixed  with  five  times  its  weight 
of  pure  carbonate  of  lime,  and  the  mixture  exposed  in  a 
platinum  crucible,  protected  as  above,  to  the  strongest  heat  of 
an  air-furnace  for  about  half  an  hour.  The  mass,  which  is 
not  fused,  but  sintered  together,  is  then  digested  in  dilute 
hydrochloric  acid ;  the  silica  separated  as  before ;  the  greater 
part  of  the  lime  and  likewise  the  bases  of  the  silicate  precipi- 
tated by  carbonate  of  ammonia  and  free  ammonia ;  the  filtrate 
evaporated  to  dryness,  and  the  ammoniacal  salts  expelled  by 
ignition ;  the  residue  redissolved  in  w^ater ;  the  remainder  of 
the  lime  precipitated  by  oxalate  of  ammonia ;  and  the  ammo- 
niacal salts  again  expelled  by  evaporation  and  ignition.  The 
residue  then  contains  nothing  but  the  chlorides  of  the  fixed 
alkalies  and  magnesia,  if  that  substance  was  contained  in  the 
mineral.  Carbonate  of  baryta  may  also  be  used  instead  of 
carbonate  of  lime,  and  the  excess  of  baryta  removed  by  sul- 
phuric acid. 

Another  method  of  obtaining  the  alkalies  in  a  silicate,  is  to 


MODIFICATIONS   OF    SULPHUR.  679 

decompose  it  with  hydrofluoric  acid  aided  by  a  gentle  heat. 
The  acid  must  be  added  by  small  portions  to  the  finely 
pulverised  mineral  contained  in  a  platinum  dish,  till  the  action 
ceases  and  the  whole  is  reduced  to  a  pasty  mass.  This  mass 
is  then  heated  with  strong  sulphuric  acid,  which  expek 
fluoride  of  silicon  and  hydrofluoric  acid :  the  residue  is 
heated  to  low  redness  to  expel  the  excess  of  sulphuric  acid  ; 
the  dry  mass,  when  cold,  moistened  with  strong  hydrochloric 
acid,  and,  after  standing  for  about  half  an  hour,  digested  with 
water.  The  whole  then  dissolves,  provided  the  decomposition 
by  the  hydrofluoric  acid  has  been  complete.  The  solution 
contains  the  alkalies  and  the  other  bases  in  the  state  of  sul- 
phates, 

SULPHUR. 

AUotropic  Modifications  of  Sulphur  (I.  396). — Among  the 
various  modifications  of  sulphur,  there  are,  according  to  Ber- 
thelot*,  two  principal  states  which  are  more  stable  than  the 
rest,  and  are,  in  fact,  the  limits  to  which  all  the  others  may 
be  reduced.  These  are,  first,  the  octohedral,  or  electro -negative 
sulphur,  which  acts  as  a  supporter  of  combustion,  and  the 
electro-positive,  or  combustible  sulphur,  which  is  generally 
amorphous  and  insoluble  in  bisulphide  of  carbon,  alcohol,  &c. 

Allied  to  octohedral  sulphur  are  two  conditions  of  inferior 
stability,  viz.  the  prismatic  variety,  which  crystallises  from 
melted  sulphur,  and  the  soft  emulsionable  sulphur  (milk  of 
sulphur),  precipitated  from  the  solution  of  an  alkaline  poly- 
sulphide  by  the  action  of  acids.  Both  these  varieties  of  sulphur 
are  soluble  in  bisulphide  of  carbon,  and  change  spontaneously 
into  octohedral  sulphur  after  a  certain  time. 

Electro-positive  sulphur,  properly  so  called,  is  that  which  is 
obtained  when  sulphur  separates  from  any  of  its  compounds 
with  oxygen,  chlorine,  bromine,  &c.,  the  chloride  or  bro- 
mide yielding  the  most  stable  variety.     It  is  amorphous  and 

*   Ann.  Ch   Phys.  [3],  xlix.  430. 
3  A  2 


680  SULPHUR. 

insoluble  in  solvents  properly  so  called,  that  is  to  say,  in 
liquids  which  do  not  act  upon  it  chemically,  such  as  water, 
alcohol,  ether,  bisulphide  of  carbon,  &c. 

To  this  electro-positive  sulphur  are  allied  several  modifi- 
cations more  or  less  distinct,  which  may  perhaps  be  reduced 
to  three  principal  varieties,  all  amorphous,  but  less  stable  than 
the  one  just  mentioned,  viz.  the  soft  sulphur  precipitated  from 
solutions  of  the  hyposulphites ;  the  insoluble  sulphur  obtained 
by  exhausting  flowers  of  sulphur  with  alcohol  and  bisulphide 
of  carbon ;  and  the  insoluble  sulphur  obtained  by  exhausting 
with  bisulphide  of  carbon  the  soft  sulphur  produced  by  the 
action  of  heat.  These  varieties  are  distinguished  one  from 
the  other  by  the  greater  or  less  facility  with  which  they  are 
transformed  into  soluble  crystallisable  sulphur,  either  by  a 
temperature  of  100°  C,  or  by  contact  with  certain  electro- 
positive bodies,  such  as  the  alkalies  and  their  sulphides,  an 
alcoholic  solution  of  hydrosulphuric  acid,  &c.  By  the  con- 
trary influences,  that  is  to  say,  by  contact  with  bodies  having 
a  decided  electro-negative  character,  they  may  all  be  reduced 
to  the  most  stable  insoluble  variety,  viz.  that  which  is  de- 
posited from  the  chloride  or  bromide  of  sulphur. 

The  particular  modification  which  sulphur  assumes  when 
separated  from  any  of  its  compounds,  depends  essentially  on 
the  nature  of  that  compound.  It  is  altogether  independent 
of  the  state  of  the  sulphur  previous  to  combination,  and  like- 
wise of  the  reagent  which  produces  the  separation,  provided 
that  reagent  has  neither  a  decided  electro-positive  character, 
such  as  the  alkalies,  nor  a  decided  electro-negative  or  oxidising 
character,  and  provided  that  it  acts  rapidly  and  without  any 
considerable  evolution  of  heat.  The  influence  of  these  latter 
conditions,  is  due  chiefly  to  the  unequal  stability  of  the  several 
modifications  of  sulphur.  Of  all  these  varieties,  the  octo- 
hedral  sulphur  is  the  most  stable,  and  that  to  which  all  the 
others,  even  the  most  electro-positive,  tend  to  return,  espe- 
cially under  the  influence  of  heat.     (Berthelot.) 


MODIFICATIONS    OF    SULPHUR.  681 

Sulphur,  deposited  at  the  positive  pole  of  the  voltaic 
battery  in  the  electrolysis  of  an  aqueous  solution  of  hydrosul- 
phuric  acid,  is  soluble  in  bisulphide  of  carbon  and  crystallisable ; 
but  that  which  is  deposited  at  the  negative  pole  in  the  electro- 
lysis of  sulphurous  or  sulphuric  acid,  is  insoluble  in  bisulphide 
of  carbon.  (Berthelot.*) 

Magnus  f  obtained  a  hlach  modification  of  sulphur  by  re- 
peatedly heating  sulphur  to  300°  C,  cooling  suddenly,  and  ex- 
hausting with  bisulphide  of  carbon ;  and  this  black  sulphur, 
heated  to  a  temperature  between  130°  and  150°,  passed  into  a 
red  modification.  According  to  Mitscherlich,  however,  pure 
sulphur  does  not  exhibit  these  modifications,  but  when  sulphur 
is  melted  with  small  quantities  of  fatty  matters,  various 
highly  coloured  products  are  obtained.  Even  the  grease  im- 
parted by  touching  sulphur  with  the  fingers,  is  sufficient  to 
alter  its  colour  considerably  when  melted. 

Vapour  of  sulphur,  when  it  comes  in  contact  with  cold  bodies, 
condenses  in  the  form  of  utricles,  that  is  to  say,  of  globules 
composed  of  a  soft  external  pellicle  filled  with  liquid  sulphur. 
They  sometimes  retain  their  liquid  form  for  a  considerable 
time.  This  utricular  condition  has  also  been  observed  in 
selenium,  iodine,  phosphorus,  and  arsenious  acid.     (Brame.f) 

Respecting  the  melting  point  of  sulphur,  the  observations 
of  different  experimenters  vary  from  104*5°  to  112*2°  C.  This 
discrepancy  is  attributed  by  Professor  Brodie  §  to  the  fact  that 
the  melting  point  of  sulphur  varies  according  to  its  allotropic 
state.  According  to  the  observations  of  that  chemist,  rhombic 
or  octohedral  sulphur  (crystallised  from  bisulphide  of  carbon, 
alcohol,  or  benzol)  melts  at  1 14*5°  C.  ;  but,  between  100°  and 
114-5°,  it  is  transformed  into  the  oblique  prismatic  modifica- 
tion, which  melts  at  120°,  and  if  not  afterwards  more  strongly 

*  Pogg.  Ann.  xcii.  308. 
•f  Ann.  Ch.  Pharm.  ci.  58. 
X  Compt.  rend.  xxix.  657;  xxxiii.  538,  579. 
§  Proceedings  of  the  Royal  Society,  vii.  24. 
3  A  3 


682  SULPHUR. 

heated,  solidifies  at  nearly  the  same  point.  If,  however,  its 
temperature  be  further  raised,  it  does  not  solidify  till  cooled 
to  11 1*5%  and  if  it  be  then  heated,  melts  at  a  point  very  little 
higher.  In  fact,  above  120°,  sulphur  begins  to  pass  into 
the  plastic  state,  which  is  more  fusible.  The  variety  in- 
soluble in  bisulphide  of  carbon  has  a  melting  point  consi- 
derably above  120°.  The  gradual  loss  of  transparency  of  the 
prismatic  sulphur  crystallised  from  fusion,  arises,  according 
to  Brodie,  from  the  hardening  of  plastic  sulphur  mechanically 
enclosed  within  the  crystals.  When  crystals  which  have 
thus  lost  their  transparency,  are  digested  in  bisulphide  of 
carbon,  a  portion  always  remains  undissolved.  If  sulphur 
which  has  been  fused  and  strongly  heated,  be  suddenly 
cooled  by  a  mixture  of  solid  carbonic  acid  and  ether,  it 
solidifies  in  a  hard,  perfectly  transparent  mass,  w^hich  becomes 
soft  and  elastic  at  ordinary  temperatures.  This  appears, 
indeed,  to  be  the  solid  state  of  plastic  sulphur. 

Formation  of  Anhydrous  Sulphuric  acid.  —  When  a  dry 
mixture  of  2  vols,  sulphurous  acid  and  1  vol.  oxygen  or 
atmospheric  air,  is  passed  through  a  red-hot  glass  tube  con- 
taining certain  metallic  oxides,  e.  g.  cupric,  ferric,  or  chromic 
oxide,  the  gases  unite  and  produce  dense  white  fumes  of  anhy- 
drous sulphuric  acid.  A  mixture  of  the  oxides  of  copper 
and  chromium  induces  the  combination  with  peculiar  facility. 
These  oxides  appear  to  be  capable  of  inducing  the  combina- 
tion of  unlimited  quantities  of  sulphurous  acid  and  oxygen. 
Spongy  metallic  copper  produces  the  same  effect  when  heated, 
but  not  till  the  copper  has  become  oxidised.  Clean  polished 
platinum  foil,  or  spongy  platinum,  produces  the  combination 
considerably  below  a  red  heat,  but  not  at  ordinary  tempera- 
tures.    (Wohler.*) 

Sulphide  of  Nitrogen  (I.  424). — This  body  was  discovered 
by  Soubeiran,  who  assigned  to  it  the  formula  NS^ ;  but  it  has 

♦  Ann.  Ch.  rharm.  Ixxxi.  255. 


SULPHIDE  OF  NITROGEN.  683 

since  been  more  minutely  examined  by  Fordos  and  Gelis*, 
who  have  shown  that  its  true  formula  is  NSg.  The  best 
mode  of  preparing  it  is  to  pass  dry  ammoniacal  gas  into  a 
solution  of  protochloride  of  sulphur,  SCI,  in  eight  or  ten 
times  its  volume  of  bisulphide  of  carbon.  Crystals  of  sal- 
ammoniac  are  then  deposited,  and  the  solution  becomes  darker 
in  colour,  and  deposits  cochineal-coloured  flakes,  which  soon 
decompose  and  turn  brown.  An  excess  of  ammonia  de- 
composes this  brown  compound.  The  current  of  gas  must 
be  continued  till  the  solution  acquires  an  orange-yellow 
colour,  and  contains  only  very  slightly  coloured  flakes,  which 
may  be  separated  by  filtration.  The  filtrate,  when  left  to 
evaporate,  deposits  crystals  of  sulphur,  while  the  sulphide  of 
nitrogen  remains  in  the  mother  liquid,  and  may  be  obtained 
by  further  evaporation  of  the  decanted  liquid.  The  reaction 
is  as  follows  :  •  — 

3SC1  +  4NH3  =  NS2  +  S  +  3NH,C1. 

At  the  same  time,  however,  there  are  a  number  of  inter- 
mediate  products  formed  (the  brown  flocculent  matters 
above-mentioned),  consisting  of  compounds  of  sulphide  of  ni- 
trogen with  chloride  of  sulphur,  viz.,  SCI .  NSg ;  SCI .  2NS2 ' 
and  SCI  .  SNSj ;  but  these  are  all  ultimately  decomposed  by 
excess  of  ammonia.  Sulphide  of  nitrogen  forms  similar  com- 
pounds with  dichloride  of  sulphur,  SgCl. 

Sulphide  of  nitrogen  is  insoluble  in  water,  slightly  soluble 
in  alcohol,  wood-spirit,  ether,  and  oil  of  turpentine  ;  bisulphide 
of  carbon  dissolves  it  to  the  amount  of  15  parts  in  1000,  and 
the  solution  deposits  the  compound  in  small  elongated  prisms 
derived  from  the  right  rhomboidal  prism,  and  terminated 
with  dihedral  summits ;  they  are  transparent  and  of  a  golden 
yellow  colour.  The  solution  must,  however,  be  evaporated 
immediately,  for  it  decomposes  after  a  short  time,  yielding 
hydrosulphocyanic   acid,    and  a  yellow  substance   like   that 

'*  Conspt.  rend.  xxxi.  702. 
3  A  4 


684  SULPHUR. 

which  is  commonly  called  sulphocyanogen.  Water  slowly 
decomposes  sulphide  of  nitrogen,  yielding  free  ammonia,  toge- 
ther with  hyposulphurous  and  trithionic  acids  : — 

4NS2  +  15H0  =  NH,0.  S2O2  +  2(1^40.8305)  +  NH3. 

Protosulphide  of  Carbon,  CS.  —  This  compound  is  obtained  : 

1.  By  passing  the  vapour  of  bisulphide  of  carbon  over  spongy 
platinum  or  pumice-stone  heated  to  redness ;  sulphur  is  then 
deposited,  and  the  protosulphide  liberated  in  the  form  of  gas. 

2.  In  the  preparation  of  the  bisulphide,  and  simultaneously 
therewith.  3.  By  decomposing  the  vapour  of  the  bisulphide 
at  a  red  heat  by  means  of  lamp-black,  wood-charcoal,  and 
especially  by  animal  charcoal  in  fragments.  4.  By  decom- 
posing the  vapour  of  the  bisulphide  at  a  red  heat  with  hydro- 
gen. 5.  By  calcining  sulphide  of  antimony  with  excess  of 
charcoal.  6.  By  the  action  of  carbonic  oxide  on  hydrosul- 
phuric  acid  at  a  red  heat :  — 

CO  +  HS  =  HO  +  CS. 

7.  By  the  action  of  sulphurous  acid,  or  chloride  of  sulphur, 
on  olefiant  gas  at  a  red  heat.  8.  In  the  decomposition  of 
sulphocyanogen  by  heat,  &c. 

The  first  process  yields  the  gas  tolerably  pare ;  that  which 
is  obtained  by  the  other  processes  is  mixed  with  hydrosul- 
phuric  acid,  and  carbonic  oxide.  It  is  purified  by  passing  it 
rapidly  through  solutions  of  acetate  of  lead,  and  dichloride  of 
copper  dissolved  in  hydrochloric  acid,  then  dried  and  collected 
over  mercury. 

Protosulphide  of  carbon  is  a  colourless  gas,  having  a 
strongly  ethereal  odour,  resembling  that  of  the  bisulphide, 
but  not  disagreeable.  When  breathed  in  too  large  a  quantity, 
it  appears  to  be  powerfully  ansBsthetic.  It  burns  with  a  fine 
flame,  producing  carbonic  and  sulphurous  acids,  and  a  little 
sulphur.  Its  density  is  somewhat  greater  than  that  of  car- 
bonic acid.     It  does  not  liquefy  at  the  temperature  of  a  mix- 


SULPHIDES   OF    CARBON.  685 

tare  of  ice  and  salt.  Water  dissolves  nearly  its  own  volume 
of  this  gas  ;  but  decomposes  it  somewhat  quickly  into  hydro- 
sulphuric  acid  and  carbonic  oxide.  It  is  scarcely  more 
soluble  in  alcohol  or  ether.  It  is  not  absorbed  by  a  solu- 
tion of  dichloride  of  copper.  Acetate  of  lead  is  slowly 
blackened  by  it.  It  is  rapidly  decomposed  by  solutions  of 
the  caustic  alkalies.  With  lime-water,  it  yields  sulphide  of 
calcium,  and  a  volume  of  carbonic  oxide  equal  to  its  own  :  — 

CaO  +  CS  =  CaS  +  CO. 

This  reaction  establishes  its  composition,  which  is  further  con- 
firmed by  the  fact,  that,  when  exploded  with  oxygen,  it  yields 
equal  volumes  of  carbonic  and  sulphurous  acids.  At  a  red 
heat,  it  is  slightly  decomposed:  1.  By  spongy  platinum; 
2.  By  aqueous  vapour,  into  HS  and  CO  ;  3.  More  readily 
by  hydrogen  into  HS  and  a  hydrocarbon ;  4.  Completely  by 
copper,  yielding  sulphide  of  copper,  and  graphitoidal  carbon ; 
5.  By  an  equal  volume  of  chlorine  in  sunshine,  with  formation 
of  products  not  yet  examined.     (Baudrimont.*) 

Bisulphide  of  Carbon.  —  By  the  action  of  nascent  hydrogen 
(generated  by  slowly  decomposing  hydrochloric  acid  witli 
zinc)  upon  bisulphide  of  carbon,  Girardf  has  obtained  a 
compound,  CHS,  which  is  neutral  to  vegetable  colours,  has 
a  powerful  odour,  is  insoluble  in  water,  dissolves  sparingly 
in  alcohol,  ether,  and  rock-oil,  more  readily  in  chloroform 
and  bisulphide  of  carbon,  but  most  readily  in  benzol ;  crys- 
tallises from  its  solutions  in  square  prisms ;  sublimes  unde- 
composed  at  150°  C.  in  long  needles ;  but  decomposes  at  200°. 
It  is  not  altered  by  alkalies ;  dissolves  in  warm  hydrochloric 
acid ;  and  is  decomposed  by  nitric  and  by  strong  sulphuric 
acids.  It  forms  crystalline  compounds  with  nitrate  of  silver, 
and  with  the  chlorides  of  platinum,  gold,  and  mercury. 

Bisulphide  of  carbon,  enclosed  with  water  in  a  sealed  tube, 

*  Compt.  rend.  xHv.  1000. 
f  Corapt.  rend,  xliii.  396. 


686  SULPHUR. 

and  heated  for  three  or  four  hours  to  150°  C,  is  resolved  into 
carbonic  and  hydrosulphuric  acids.  Many  metallic  oxides 
and  salts,  treated  in  a  similar  manner  with  bisulphide  of  car- 
bon, yield  carbonic  acid  and  a  metallic  sulphide.  (Schlag- 
denhauflPen.*) 

Quantitative  estimation  of  Sulphur  and  its  compounds. — 
Sulphur  is  almost  always  estimated  in  the  form  of  sulphuric 
acid.  To  determine  the  quantity  of  sulphur  in  a  metallic 
sulphide,  the  compound  is  heated  with  nitric  acid,  aqua-regia, 
or  sometimes  with  a  mixture  of  hydrochloric  acid  and  chlorate 
of  potash,  till  the  metal  is  oxidised,  and  the  sulphur  converted 
into  sulphuric  acid.  The  solution  is  then  treated  with 
chloride  of  barium  or  nitrate  of  baryta,  and  the  precipi- 
tated sulphate  of  baryta  collected  on  a  filter,  washed,  dried, 
and  ignited.  Before  adding  the  baryta-solution,  however, 
the  liquid  must  be  considerably  diluted  with  water,  be- 
cause the  nitrate  and  chloride  of  barium  are  themselves  in- 
soluble in  strong  nitric  and  hydrochloric  acids.  The  liquid 
is  then  boiled,  and  afterwards  left  to  stand  till  the  precipitate 
has  completely  settled  down ;  after  which  the  clear  liquid  is 
first  passed  through  the  filter,  and  then  the  precipitate 
thrown  upon  it ;  if  the  precipitate  be  poured  upon  the  filter 
before  it  has  settled  down,  it  will  be  sure  to  run  through. 
As  the  oxidation  of  the  sulphur  is  very  slow,  the  metal  being 
completely  oxidised  and  dissolved  long  before  it,  and  a  por- 
tion of  the  sulphur  separated  in  the  free  state,  it  is  some- 
times convenient  to  collect  this  portion  on  a  small  weighed 
filter,  determine  its  amount  by  direct  weighing,  and  after- 
wards estimate  the  dissolved  portion  as  above. — In  the  sul- 
phides of  gold  and  platinum,  from  which  the  sulphur  is  com- 
pletely expelled  by  ignition,  its  quantity  may  be  at  once 
determined  by  weighing  the  residual  metal.  The  sulphides 
of  the  alkali-metals  and  alkaline  earth-metals  are  sometimes 

•  J.  Pharm.  [.'i],  xxix.  401. 


ESTIMATION   OF   SULPHUK.  687 

analysed  by  decomposing  them  with  hydrochloric  acid,  re- 
ceiving the  evolved  hydrosulphuric  acid  in  a  solution  of 
acetate  of  lead,  oxidising  the  precipitated  sulphide  of  lead  with 
fuming  nitric  acid,  weighing  the  sulphate  of  lead  thus  pro- 
duced, and  thence  calculating  the  quantity  of  sulphur. 

The  sulphur  in  organic  compounds  may  likewise  be  esti- 
mated by  oxidising  the  compound  with  fuming  nitric  acid, 
and  precipitating  the  resulting  sulphuric  acid  with  a  baryta- 
solution.  Another  method,  given  by  Dr.  W.  J.  Russell*,  is 
to  burn  the  substance  in  a  combustion- tube  with  oxide  of 
mercury,  carbonate  of  soda  being  added  to  take  up  the  sul- 
phuric acid  produced,  and  a  small  bent  tube  dipping  under 
water  fitted  into  the  open  end  of  the  combustion-tube,  so  that 
any  acid  vapours  that  escape  may  be  condensed  in  the  water. 
At  the  end  of  the  combustion,  this  liquid  is  acidulated  with 
hydrochloric  acid;  the  tube  washed  out  with  the  acid  solution; 
the  liquid  filtered;  and  the  sulphuric  acid  precipitated  by 
chloride  of  barium. 

The  quantity  of  sulphuric  acid  in  a  soluble  sulphate  is 
estimated  by  precipitating  the  aqueous  solution  with  chloride 
of  barium.  Some  sulphates  which  are  insoluble  in  water 
may  be  dissolved  in  hydrochloric  or  nitric  acid,  and  the 
baryta-solution  then  added.  The  sulphates  of  lime,  strontia, 
and  lead  may  be  decomposed  by  boiling  with  a  solution  of 
carbonate  of  soda  (II.  598),  and  the  sulphuric  acid  preci- 
pitated by  chloride  of  barium  from  the  filtered  solution, 
previously  acidulated  with  nitric  or  hydrochloric  acid.  Sul- 
phate of  baryta  must  be  decomposed  by  fusion  in  a  platinum 
crucible  with  three  times  their  weight  of  carbonate  of  soda; 
the  fused  mass  digested  in  water;  the  filtered  soda-solution 
acidulated  ;  and  the  sulphuric  acid  precipitated  as  above. 

Sulphurous  and  hyposulphurous  acid  may  be  estimated  by 
oxidation  with  nitric  acid,  whereby  they  are  converted  into 
sulphuric  acid,  or  by  Bunsen*s  iodometric  method  (p.  722). 

*  Chim.  Sue.  Qit.  J.  vii.  212. 


688  SELENIUM. 


SELENIUM. 


Preparation  of  Selenium  (I.  427). — This  element  is  extracted 
from  natural  selenides,  and  principally  from  the  seleniferous 
ores  of  the  Harz,  by  the  following  process : — The  pulverised 
ore  is  treated  with  hydrochloric  acid,  to  remove  the  earthy 
carbonates  with  which  it  is  mixed.  The  residue,  after  being 
well  washed  and  dried,  is  mixed  with  its  own  weight  of  black 
flux,  and  calcined  for  an  hour  at  a  red  heat.  Selenide  of 
potassium  is  thus  formed,  which  is  separated  by  washing  the 
cooled  and  rapidly  pulverised  residue  with  boiling  water.  A 
brown-red  solution  is  thus  obtained,  and  the  insoluble  matter 
which  remains  on  the  filter  retains  the  metals  (copper,  lead, 
and  silver)  which  were  combined  with  the  selenium.  The  solu- 
tion of  selenide  of  potassium  oxidises  gradually  on  exposure 
to  the  air,  potash  being  formed,  and  the  selenium  collecting 
in  a  grey  mass,  which  is  carefully  washed,  dried,  and  dis- 
tilled. 

When  the  selenium  contains  sulphur,  it  is  converted  into 
seleniate  and  sulphate  of  potash  by  calcination  with  a  mixture 
of  nitre  and  carbonate  of  potash.  The  calcined  mass  is  dis- 
solved in  hydrochloric  acid,  and  the  liquid  saturated  with  sul- 
phurous acid  gas,  and  heated  to  the  boiling  point.  The  selenic 
acid  is  thereby  reduced,  and  the  selenium  precipitated  in  red 
flakes,  while  the  sulphate  of  potash  remains  in  solution. 
(Wohler.*) 

Modifications  of  Selenium,  —  Berzelius  found  that  selenium 
solidifies  in  the  amorphous  state  by  sudden,  and  in  the  crys- 
talline state  by  slow  cooling.  Hittorff  finds  that  crystalline 
(or  granular)  selenium  melts  at  211 -5° C.  (4r2-6°F.),  without 
previous  softening.  The  mass,  when  left  to  cool  slowly, 
remains  fluid  below  that  temperature,  and  solidifies  very  gra- 
dually in  the  amorphous  state;  a  thermometer  immersed  in  it 

*  Traite  de  Chimie  generale,  par  Pelouzc  et  Frcmy,  2iiie.  edition,  i.  430. 


SELENIUM.  689 

during  the  cooling  does  not  remain  stationary  at  any  point,  or 
indicate  any  temperature  at  which  the  latent  heat  of  the 
selenium  is  set  free.  Amorphous  selenium  retains  its  condi- 
tion for  a  long  time  at  ordinary  temperatures ;  but  between 
80°  and  217°C.  (176°  and  412-6°F.),  it  becomes  crystalline 
and  gives  out  great  heat,  most  quickly  between  125°  and 
180°  C.  (257°  and  356°  F.),  and  when  pulverised.  When 
amorphous  selenium  is  heated  in  an  air-bath  to  between  125° 
and  130°  C,  a  thermometer  immersed  in  it  rises  suddenly 
to  between  210°  and  215°  C.  Selenium,  as  precipitated  in  the 
red,  finely  divided  state  from  selenious  acid  by  sulphurous 
acid  and  other  reducing  agents,  or  from  an  aqueous  solution 
of  seleniuretted  hydrogen  by  exposure  to  the  air,  is  amorphous, 
and  exhibits  the  above-mentioned  spontaneous  rise  of  tempera- 
ture when  heated.  Selenium  deposited  from  solutions  of 
selenide  of  potassium  or  ammonium  by  exposure  to  the  air,  is 
crystalline,  and  has  a  sp.  gr.  of  4*808  at  60°r.  These  modi- 
fications of  selenium  are  analogous  to  those  of  sulphur  (p.  679). 
Berthelot  finds  that  selenium  deposited  at  the  positive  pole  in 
the  electrolysis  of  hydroselenic  acid,  is  soluble  in  bisulphide 
of  carbon ;  but  that  which  is  deposited  at  the  negative  pole  in 
the  electrolysis  of  selenious  acid  is  insoluble.  Amorphous 
selenium  does  not  conduct  electricity ;  crystalline  selenium 
conducts  it  much  better,  and  its  conducting  power  increases 
rapidly  with  its  tem.perature.     (Hittorff.*) 

Quantitative  estimation  of  Selenium,— ^The  methods  for  the 
estimation  and  separation  of  selenium  are  similar  to  those 
which  are  applied  to  tellurium  (p.  201).  -  When  in  the  form 
of  selenious  acid,  it  is  precipitated  in  the  free  state  by  sul- 
phurous acid.  Selenic  acid  must  first  be  reduced  to  selenious 
acid  by  heating  with  hydrochloric  acid ;  it  may  also  be  pre- 
cipitated as  a  baryta-salt,  like  sulphuric  acid.  Selenious  and 
selenic   acid   may  be   separated  from  certain    metals,   iron, 

*  Pogg.  Ann.  Ixxxiv.  214. 


690  PHOSPHORUS. 

zinc,  &c.,  by  hydrosulphuric  acid,  which  throws  down  sul- 
phide of  selenium  ;  from  others,  such  as  copper,  silver,  and 
lead,  by  sulphide  of  ammonium,  which  dissolves  sulphide  of 
selenium.  Metallic  selenides  may  be  decomposed  by  heating 
them  in  a  current  of  chlorine  gas,  the  volatile  chloride  of 
selenium  being  received  in  water,  which  decomposes  it  and 
precipitates  the  selenium. 

PHOSPHORUS. 

Red  or  amorphous  Phosphorus  (L  431). — When  phos- 
phorus is  subjected  to  the  action  of  the  sun's  rays,  or  to  a  high 
temperature  in  vacuo,  or  in  a  gas  which  does  not  act  upon  it 
chemically,  it  quickly  assumes  a  red  colour,  and  becomes 
completely  altered  in  its  properties.  This  modified  phosphorus 
may  be  obtained  in  considerable  quantity  by  heating  ordinary 
phosphorus  to  230°-250°C.  (446°~482°F.)  in  a  retort  filled 
with  nitrogen  or  carbonic  acid,  and  having  adapted  to  its 
beak  a  bent  tube  which  dips  under  mercury.  Part  of  the 
phosphorus  condenses  on  the  neck  of  the  retort  in  the  ordinary 
state,  but  the  rest  is  transformed  in  the  course  of  a  few  hours 
into  a  dark -red  mass,  which  is  a  mixture  of  amorphous  and 
ordinary  phosphorus.  On  treating  this  mixture  with  bisul- 
phide of  carbon,  the  latter  is  dissolved,  and  the  amorphous 
phosphorus  remains  in  form  of  a  red  powder. 

This  amorphous  phosphorus  differs  remarkably  from  ordi- 
nary phosphorus,  both  in  its  physical  and  in  its  chemical  pro- 
perties. Its  sp.  gr.  at  10°  C.  (50°  F.)  is  1*964,  while  that  of 
ordinary  phosphorus  is  between  1*826  and  1*840;  it  sinks  in 
melted  phosphorus,'  the  density  of  that  liquid  at  45°  C.  being 
1*88.  It  melts  at  250°  C,  and  at  260°  is  reconverted  into 
ordinary  phosphorus.  Red  phosphorus  is  much  less  ener- 
getic in  its  chemical  affinities  than  ordinary  phosphorus.  At 
ordinary  temperatures  it  has  no  perceptible  odour,  and  may 
be  exposed  to  the  air  without  alteration.  It  does  not  become 
luminous  in  the  air  till  heated  to  200°  C,  or  take  fire  below 


AMORPHOUS   PHOSPIIOraJS.  691 

260°.  It  does  not  combine  with  melted  sulphur.  It  combines 
with  chlorine  without  emission  of  light ;  with  bromine,  how- 
ever, it  exhibits  that  phenomenon.  It  is  insoluble  in  bisul- 
phide of  carbon,  alcohol,  ether,  rock-oil,  and  terchloride  of 
phosphorus.  Oil  of  turpentine  and  a  few  other  liquids  dis- 
solve small  quantities  of  it  (Schrotter*). 

Amorphous  phosphorus  may  be  obtained  in  the  compact 
state  by  keeping  phosphorus  for  several  days  at  a  temperature 
a  little  below  260°  C.  It  is  then  converted  into  a  brittle,  easily 
friable,  reddish-brown  mass,  having  a  concho'idal  fracture,  and 
exhibiting  on  the  fractured  surface,  an  iron-grey  colour  and 
imperfect  metallic  lustre.  As  thus  prepared,  however,  it  is 
not  quite  pure,  but  contains  a  small  quantity  of  ordinary 
phosphorus,  which  causes  it  to  oxidate  at  ordinary  tempera- 
tures. The  density  of  this  compact  red  phosphorus  was  found 
to  be  between  2*089  and  2*106;  if  quite  pure,  it  would  be 
still  denser  (Schrotterf). 

Phosphorus  may  also  be  brought  to  the  amorphous  state  by 
heating  it  with  a  small  quantity  of  iodine.  When  phosphorus 
is  melted  in  a  glass  vessel  filled  with  carbonic  acid  gas,  and  a 
small  quantity  of  iodine  introduced  through  an  upright  glass 
tube  reaching  nearly  to  the  phosphorus,  a  violent  action  takes 
place,  attended  with  great  rise  of  temperature,  and  a  hard,  black, 
semi-metallic  mass  is  produced,  which  yields  a  red  powder. 
The  same  result  is  obtained  when  phosphorus  is  melted  under 
strong  hydrochloric  acid,  and  a  small  quantity  of  iodine  added  ; 
under  water  the  experiment  does  not  succeed.  The  product 
thus  obtained  is  nearly  pure  amorphous  phosphorus,  contain- 
ing only  a  trace  of  iodine ;  when  strongly  heated,  it  distils 
over  almost  without  alteration,  the  distillate  containing  only 
a  trace  of  ordinary  phosphorus.  The  mode  of  its  formation 
appears  to  be  this  :  — An  iodide  of  phosphorus  is  first  formed, 
probably  Pig,  and  the  phosphorus  contained  in  it  passes  into 

•  Wien.  Akad.  Ber.  1848,  130  ;  Ann.  Ch.  Phys.  [3],  xxiv.  406. 
f  Pogg.  Ann.^  Ixxxi.  299 ;  Compt.  rend.  xxxi.  138, 


692  rnosPHORUS. 

the  amorphous  state  ;  this  compound  is  then  decomposed,  the 
amorphous  phosphorus  separated,  and  a  more  volatile  iodine 
compound  formed,  which  acts  upon  another  portion  of  phos- 
phorus with  the  same  final  result,  so  that  by  repetition  of  these 
processes  a  large  quantity  of  phosphorus  may  be  brought 
into  the  amorphous  state  (Brodie*).  Amorphous  phosphorus 
thus  prepared  differs  in  some  respect  from  that  which  is 
obtained  by  the  action  of  heat,  being  more  readily  attacked 
by  potash,  and  precipitating  certain  metallic  solutions  {e.  g. 
sulphate  of  copper),  an  effect  which  may  perhaps  be  due  to 
the  small  quantity  of  iodine  contained  in  it.  The  sp.  gr.  of 
this  amorphous  phosphorus  is  2 '23. 

The  formation  of  amorphous  phosphorus  under  the  influ- 
ence of  iodine  shows  that  it  possesses  an  electro-positive  cha- 
racter, like  amorphous  sulphur ;  a  conclusion  which  is  further 
confirmed  by  its  formation  in  a  similar  manner  under  the 
influence  of  bromine  and  chlorine,  and  by  the  imperfect 
combustion  of  phosphorus  or  phosphuretted  hydrogen  (Ber- 
thelot).  According  to  Schrotter,  the  substance  usually  re- 
garded as  oxide  of  phosphorus,  P2O,  is  nothing  more  than 
amorphous  phosphorus. 

Atomic  weight  of  Phosphorus.  —  By  burning  amorphous 
phosphorus  in  oxygen-gas,  Schrotter  finds  that  the  atomic 
weight  of  phosphorus  is  31.f 

Modifications  of  Metaphosphoric  acid  (I.  449). — This  acid 
appears  to  be  susceptible  of  five  polymeric  modifications,  viz. : 

Monometaphosphoric  acid        ....  HO.PO5 

Dimetaphosphoric  acid        2HO.2PO5 

Trimetaphosphoric  acid SHO.SPOg 

Tetrametaphosphoric  acid 4HO.4PO5 

Hexametaphosphoric  acid 6HO.6PO5 

The   formulae  of   these   several    modifications    are    deduced 

*  Chem.  Soc.  Qu.  J.  v.  289. 

f  Ann,  CIi.  Phys.  [3],  xxxviii.  131. 


METAPHOSPHORIC   ACID.  693 

chiefly  from  the  relative  numbers  of  atoms  of  the  two  bases 
in  the  double  salts  which  they  form. 

MonometapJiosphoric  acid  is  the  variety  discovered  by  Mad- 
drell.  It  is  produced  in  combination  with  potash,  when  that 
alkali  and  phosphoric  acid  are  ignited  together  in  equivalent 
proportions,  —  and,  in  combination  with  oxide  of  ammonium, 
by  heating  dimetaphosphate  of  ammonia  to  250°  C.  (482°  F.) 
It  does  not  form  any  double  salts,  and  probably  therefore 
contains  only  one  atom  of  acid  and  base :  MO.PO5. 

Dimetaphosphoric  acid  is  produced  when  phosphoric  acid  is 
heated  with  oxide  of  copper,  zinc,  or  manganese  in  equal  or 
nearly  equal  numbers  of  atoms.  The  copper-salt,  which  serves 
for  the  preparation  of  all  the  others,  is  obtained  by  heating  to 
350°  C.  (662°  F.)  a  solution  of  phosphoric  acid  and  oxide  of 
copper  in  the  proportion  of  5V0^  to  4CuO.  It  is  a  crystalline 
powder,  insoluble  in  water,  but  soluble,  with  the  aid  of  heat, 
in  sulphuric  acid  and  in  ammonia.  The  dimetaphosphates  of 
the  alkalies,  which  are  obtained  by  treating  the  copper-salt 
with  sulphide  of  potassium,  &c.,  are  soluble  in  water,  crystal- 
lisable,  and  converted  by  heat  into  insoluble  salts.  Dimeta- 
phosphoric acid  has  a  strong  tendency  to  form  double  salts, 
all  of  which  contain  equal  numbers  of  atoms  of  the  two  bases ; 
(MO.M'0).2P05;  hence  its  composition  is  inferred.  For 
example,  on  mixing  a  concentrated  solution  of  the  potash-salt 
with  chloride  of  sodium,  or  of  the  soda-salt  with  chloride  of 
potassium,  a  crystalline  double  salt  is  obtained,  having  the 
composition  (NaO.KO).2P05  +  2H0;  and  by  mixing  2  at. 
dimetaphosphate  of  ammonia  with  1  at.  chloride  of  copper, 
in  tolerably  concentrated  solutions,  and  adding  alcohol,  blue 
needle-shaped  crystals  are  formed,  containing  (CuO.NH^O). 
2PO5   +   4H0. 

Trimetaphosphoric  acid  is  produced  in  the  form  of  a  soda- 
salt  by  slowly  cooling  a  fused  mixture  of  1  at.  PO5  and 
1  at.  soda.  Its  double  salts  contain  2  atoms  of  one  base  to 
1  atom  of  the  other:  (2MO.M'0).3P05. 

VOL.  II,  3  B 


694  PHOSPHORUS. 

TetrametaphospJwric  acid  is  formed  by  heating  phosphoric 
acid  with  oxide  of  lead,  bismuth,  or  cadmium,  or  with  a  mix- 
ture of  equal  numbers  of  atoms  of  soda  and  oxide  of  copper. 
The  lead-salt  is  easily  decomposed  by  alkaline  sulphides,  and 
yields  the  corresponding  salts  of  the  alkalies.  The  soda-salt 
in  combination  with  water  is  viscid  and  elastic,  and  forms 
with  a  larger  quantity  of  water  a  gummy  mass,  which  will 
not  pass  through  a  filter.  The  double  salts  of  this  acid  con- 
tain equal  numbers  of  atoms  of  their  two  bases,  like  those  of 
dimetaphosphoric  acid ;  but  as  they  differ  in  physical  proper- 
ties from  those  of  the  latter,  it  is  probable  that  they  are  com- 
posed according  to  the  formula  (2M0.2M'0).4P05,  e.  g.  the 
copper  and  sodium  salt  =  (2CuO.  2NaO).4P05. 

Hexametapliosphoric  acid  is  the  first  discovered  modification 
of  metaphosphoric  acid  (see  page  442).  It  is  formed  by  igniting 
the  hydrate  of  phosphoric  acid,  by  the  sudden  cooling  of  the 
soda-salt,  and  by  igniting  phosphoric  acid  with  oxide  of  silver. 
It  forms  double  salts,  the  quantities  of  base  in  which  are 
nearly  in  the  proportion  of  5  at.  :  1  at. ;  hence  the  compo- 
sition of  these  salts  is  inferred  to  be:  (5MO.M'0).6P05 ; 
thus  the  soda  and  lime-salt  is  (5CaO .  NaO) .  6PO5  (Fleit- 
mann*). 

Action  of  Water  at  high  temperatures  on  the  Pyrophosphates 
and  Metaphosphates. — These  salts  heated  with  water  in  sealed 
tubes  to  280°  C.  (536°  F.),  are  decomposed,  with  formation  of 
tribasic  phosphates.  If  the  base  of  the  pyrophosphate  forms 
an  insoluble  tribasic  phosphate,  the  latter  is  precipitated,  and 
an  acid  phosphate  remains  in  solution.  Thus,  with  pyro- 
phosphate of  silver:  2(2AgO .  PO^)  +  2H0  =  3AgO 
rO,+  (Ag0.2HO).PO,. 

If  the  base  of  the  pyrophosphate  forms  a  soluble  tribasic 
phosphate,  the  product  is  a  neutral  tribasic  phosphate :  thus 

2K0  .  PO,  4-   HO  =  (2K0  .  HO)  .  PO^. 

•  Pogg.  Ann.  Ixxviii.  233,  238. 


AMIDES   OF   PHOSniORIC   ACID.  695 

The  metaphospliates  similarly  treated  yield  insoluble  phos- 
phates and  free  phosphoric  acid,  which  dissolves  small  quan- 
tities of  the  precipitated  phosphates  ;  thus  with  lime : 

SCCaO.PO^)  +  6H0  =  SCaO.PO^  +  2(3HO.PO,). 

The  metaphosphates  of  potash  and  soda  yield  acid  phos- 
phates : 

NaO.POg   +  2H0  =  Na0.2H0.P0,.* 

Sulphides  of  Phosphorus. — These  compounds  are  easily 
obtained  by  fusing  sulphur  with  amorphous  phosphorus  in  an 
atmosphere  of  carbonic  acid  ;  a  violent  action  takes  place,  but 
no  explosion  (Kekule  f ), 

Amides  of  Phosphoric  acid. — 1.  Triphosphamide,  NgHgPOj 

cPO, 
=  N3]    Hg. —  When  dry  ammoniacal  gas  is  slowly  passed  into 

^    H3 
oxychloride  of  phosphorus  (chloride  of  phosphoryl,  POg.Clg), 
and  the  product  afterwards  treated  with  water,  a  solution  of 
sal-ammoniac  is  obtained,  together  with  a  snow-white,  amor- 
phous insoluble  substance,  which  is  triphosphamide : 

PO2CI3   +   6NH3  =   3NH,C1   4-   N3H6PO2. 

This  compound  is  scarcely  attacked  by  continued  boiling 
with  water,  potash-ley,  or  dilute  acids.  It  is  very  slowly 
decomposed  by  boiling  with  strong  nitric  or  hydrochloric 
acid,  more  readily  by  aqua-regia.  Strong  sulphuric  or  nitro- 
sulphuric  acid  dissolves  it  easily  at  a  gentle  heat,  forming  a 
solution  which  contains  ammonia  and  phosphoric  acid.  It  is 
not  completely  decomposed  by  heating  with  soda-lime.  When 
fused  with  hydrate  of  potash,  it  gives  off  a  large  quantity  of 
ammonia,  and  leaves  phosphate  of  potash.  Heated  alone,  out 
of  contact  of  air,  it  also  gives  oflP  ammonia,  and  leaves  mono- 

*  A.  Rcynoso,  Compt  rend,  xsxiv.  795. 
t  Proc.  Roy.  Soc.  vii.  38. 
3  B  2 


696  PHOSPHORUS. 

phosphamide,  which,  on  being  heated  with  potash,  evolves 
more  ammonia,  and  leaves  phosphate  of  potash.  The  com- 
pound may  be  regarded  as  tribasic  phosphate  of  ammonia 
minus  6  at.  water :  — 


By  the  action  of  anhydrous  aniline,  N .  (C^^H^) .  H .  H, 
on   oxychloride   of  phosphorus,  the  homologous   compound 

iriphenylphosphamide,  Ng.  POg.  (p\^^^  •  H3,  is  obtained  ;  it  is 
a  white  mass,  more  easily  decomposable  than  triphosphamide. 

Trinaphtylphosphamide,  N .  POg .  (C2oH7)3 .  H3,  is  obtained  in  like 

manner  by  the  action  of  naphtylamine,  N .  (CgoH^) .  H  .  H,  on 
oxychloride  of  phosphorus. 

Sulphotriphosphamide,  N3 .  PSg .  H3 .  H3,  is  obtained  by  treating 
sulphochloride  of  phosphorus,  PSgClg,  with  ammoniacal  gas ; 
it  is  also  a  white  mass,  which  is  decomposed  by  water,  with 
evolution   of  hydrosulphuric  acid  gas.     Sulphotriphenylphos- 

pJiamidef  N3 .  PS2 .  (Ci2Hg)3H3,  is  obtained  in  like  manner,  by 
the  action  of  aniline  on  sulphochloride  of  phosphorus. 
(Hugo  SchifF.*) 

2.  Bipliosphamide,  N2H3PO2  =  Ng.  POg .  H3.  (Oerhardt's  Phos- 
phamide.f)  —  Obtained  by  saturating  pentachloride  of  phos- 
phorus with  ammoniacal  gas,  and  then  boiling  with  water. 
Chlorophosphamide,  NgH^PClg,  appears  to  be  first  formed, 
and  afterwards  resolved  by  water  into  hydrochloric  acid  and 
biphosphamide : 

PCI5   4-   2NH3  =  N2H4PCI3  4-   2HC1. 
and:       N2H4PCI3   +   2H0   =  N2H3PO2   +    3HC1. 
The  product  is  purified  by  boiling,  first  with  caustic  potash, 

*  Ann.  Ch.  Pharm.  ci.  300. 

t  Ann.  Ch.  Phys.  [3],  xviii.  188. 


AMIDES   OF   PHOSPHORIC   ACID.  697 

then  with  nitric  or  sulphuric  acid,  and  finally,  by  washing 
with  water.  It  is  a  white  powder,  insoluble  in  water,  alcohol, 
and  oil  of  turpentine.  When  heated  without  access  of  air, 
it  gives  off  ammonia,  and  leaves  monophosphamide ;  but  if 
moisture  be  present,  it  yields  ammonia  and  metaphosphoric 
acid.  Fused  with  hydrate  of  potash,  it  gives  off  ammonia 
and  leaves  phosphate  of  potash.  It  resists  the  action  of  most 
oxidising  agents ;  but  is  slowly  oxidised  by  fusion  with  nitre, 
and  deflagrates  with  chlorate  of  potash.  It  may  be  regarded 
as  bi-ammoniacal  phosphate  of  ammonia  (the  so-called  neutral 
phosphate,)  minus  6H0; — 

(Nh!)%^0,-6H0  =  n/0^. 

Liebig  and  Wohler,  who  discovered  this  compound,  supposed 
it  to  be  a  bihydrate  of  phosphide  of  nitrogen,  PNg .  2 HO. 

3.  Monophosphamide  J  N  .  POg.  (Gerhardt's  Biphosphamide.)  — 
Obtained  by  heating  triphosphamide  or  biphosphamide,  with- 
out access  of  air : — 

NgHgPO^  —    2NH3  =  N.PO2 
and:  N^HgPO^  --      NH3  =  N.PO^ 

It  is  a  pulverulent  substance,  resembling  triphosphamide 
in  its  reactions,  but  still  more  difficult  to  decompose  (Ger- 
hardt,  Schiff).  It  may  be  regarded  as  ammonia,  NH3,  in 
which  the  3  at.  hydrogen  are  replaced  by  the  tribasic  radical, 
PO2,  or  as  mono-ammoniacal  phosphate  of  ammonia  (the  so- 
called  acid  phosphate),  mirnis  6H0:  — 

(NHJ.HjOe  -  6H0   =   NPO,. 

4.  Fhosphamic  acid,  NH2PO4  =  ■^-  "^j^^^aj  Q^.  —  This 
compound,  which  may  be  regarded  as  hydrated  oxide  of  am- 
monium,     tt''102  in  which  3  at.  hydrogen  in  the  ammonium 


698  PHOSPHORUS. 

are  replaced  by  PO2,  is  obtained  by  the  action  of  ammoniacal 
gas  on  anhydrous  phosphoric  acid  :  — 

Yo"]^^   +    2NH,   =   S^-^PO^JO,  +  2H0. 

Great  heat  is  evolved,  and  the  product,  when  cold,  is  a 
fused  mass,  consisting  of  phosphamic  acid  and  phosphamate 
of  ammonia,  generally  mixed  with  red  phosphorus.  On 
dissolving  this  mass  in  water,  and  filtering,  a  solution  is 
obtained,  from  which  the  other  salts,  most  of  which  are  inso- 
luble, may  be  formed  by  double  decomposition.  The  free 
acid,  which  may  be  obtained  by  decomposing  the  lime- salt 
with  sulphuric  acid,  is  a  semi-solid,  amorphous  mass,  which 
dissolves  easily  in  water  and  alcohol,  and  when  heated,  gives 
off  ammonia,  and  leaves  phosphoric  acid. 

The  phosphamates  of  the  earths  and  heavy  metals,  are 
insoluble  in  water,  and  very  sparingly  soluble  in  acids,  a 
character  which  distinguishes  them  from  the  phosphates. 
The  ammonia-salt  gives  white  precipitates  with  salts  of 
barium,  strontium,  calcium,  magnesium,  iron,  manganese, 
zinc,  lead,  mercury,  and  silver,  rose-coloured  with  cobalt, 
greenish- white  with  nickel,  light-blue  with  copper,  and  dirty 
green  with  chromium  salts.  The  iron  salt,  NHFePO^, 
dissolves  in  ammonia,  forming  a  deep  purple  solution,  which 
on  evaporation  leaves  a  crystalline  salt,  the  phosphamate  of 

NTT  PO  ) 

ferrammonium,     ^r\  y  ^[^2*    ^^^  phosphamates  of  cobalt, 

nickel,  zinc,  copper,  mercury  and  silver  likewise  dissolve  in 
ammonia,  apparently  with  formation  of  analogous  salts. 
(Schiff.*) 

5.  Phospham,  NgP.H  —  When  anhydrous  phosphoric  acid, 
saturated  as  completely  as  possible  with  ammoniacal  gas,  is 
heated  in  a  dry  current  of  that  gas,  it  is  decomposed,  and  on 
treating   the   mass  when  cold  with  water,  phosphoric   acid 

*  Ann.  Ch.  riiaim.  ciii.  1G8. 


AMIDES   OF    PHOSPHORIC   ACID.  699 

dissolves,  and  there  remains  a  small  quantity  of  a  yellowish 
red  residue,  which  gives  off  ammonia  when  fused  with 
potash,  and  exhibits  in  other  respects,  the  characters  of  phos- 
pham  (Liebig  and  Wohler's  phosphide  of  nitrogen,  I.  454). 
This  compound  is  the  nitrile  of  phosphamic  acid,  being  related 
to  it  in  the  same  manner  as  aceto-nitrile,  N .  C^Hg,  to  acetic 
acid(Schifr):— 

NH  (NHJ  PO,  -  4H0  =  N^PH. 

Gladstone*,  by  the  action  of  alkalies  on  chlorophosphide  of 
nitrogen  (p.  710),  obtained  two  acids,  azophosphoric  and  deuta- 
zophospJwric  acids,  which  he  regarded  as  phosphoric  acid 
conjugated  with  one  and  two  atoms  of  the  group  PN.  Thus 
phosphoric  acid,  =  PO5 ;  azophosphoric  acid,  =  PN.PO5; 
deutazophosphoric  acid,  =  (PN)2.P05.  These  acids,  ac- 
cording to  Gladstone's  analyses,  are  both  tribasic,  the  formula 
of  the  azophosphates  being  3M0 .  P2NO5  =  P2NM3O8: 
and  that  of  the  deutazophosphates,  3 MO  .  P3N2O5  = 
PgNgMgOg.  It  is  probable,  however,  that  deutazophosphoric 
acid  is  the  same  as  SchifTs  phosphamic  acid. 

The  formation  of  deutazophosphoric  acid  from  chlorophos- 
phide of  nitrogen  (N2P3CI5),  is  represented,  according  to 
Gladstone,  by  the  equation  — 

N2P3CI5  +  5H0  =  5HC1  +  P3N2O,. 

Laurent,  however,  has  shown  that  the  formula  of  chloro- 
phosphide of  nitrogen  is  more  probably  NPClg ;  and  from  this 
it  is  easy  to  deduce  the  formation  of  phosphamic  acid ;  — 

NPCI2  4-  4H0  =  2HC1  +  NH2PO4. 

Moreover  the  analysis  of  the  deutazophosphates  of  baryta 
and  silver  agree  with  the  formulae  of  the  phosphamates 
NHMPO4  quite  as  well  as  with  Gladstone's  formula.     By 

»  Chcm.  Soc.  Qii.  J.  iii.  135,  353. 
3  B  4 


700  PHOSPHORUS* 

decomposing  chlorophosphide  of  nitrogen  with  ammonia, 
Gladstone  obtained  in  three  experiments,  181,  183,  and  177 
per  cent,  of  an  ammoniacal  salt.  Regarding  this  as  phospha- 
mate  of  ammonia,  and  representing  its  formation  by  the 
equation — 

NPCI2  +  S^^^jO^  =  ™H^']02  +  2NH,C1  +  2H0, 

the  quantity  should  be  175  per  cent.,  which  agrees  nearly 
with  the  experimental  result. 

Azophosphoric  acid,  which  appears  to  be  a  product  of 
the  decomposition  of  deutazophosphoric  acid,  is  most  probably 

N  H     V~0 
pyrophosphamic  acid,      ^    ^tV    ^    ^j^6'  *^®  tribasic  amidogen 

acid  of  quadribasic  pyrophosphoric  acid,  V^fi^^, 

Quantitative  estimation  of  Phosphorus  and  its  compounds.  — 
Phosphorus  is  always  estimated  in  the  form  of  phosphoric 
acid.  When  it  occurs  in  combination  with  a  metal,  or  in  an 
organic  compound,  or  as  phosphorous  or  hypophosphorous 
acid,  it  is  brought  to  the  highest  state  of  oxidation  by  treat- 
ment with  nitric  acid,  aqua-regia,  or  a  mixture  of  hydro- 
chloric acid  and  chlorate  of  potash. 

The  precipitation  of  phosphoric  acid  (tribasic)  from  an 
aqueous  solution,  in  which  it  exists  in  the  free  state  or  com- 
bined with  an  alkali,  is  best  effected  by  the  addition  of  sul- 
phate of  magnesia  and  excess  of  ammonia,  chloride  of 
ammonium  being  likewise  added  to  prevent  the  precipitation 
of  magnesia  in  the  form  of  hydrate.  The  phosphoric  acid  is 
then  precipitated  as  phosphate  of  magnesia  and  ammonia, 
NH4O.2MgO.PO5.  The  precipitate  does  not  settle  down 
at  once,  but  its  deposition  may  be  accelerated  by  leaving  the 
vessel  in  a  warm  place.  Care  must  be  taken,  however,  not  to 
allow  the  liquid  to  become  very  hot,  as  in  that  case  hydrate 
of  magnesia  will  be  precipitated,  and  will  be  very  difficult 
to   rcdissolve.      Tlie    precipitate,    after    standing  for   about 


ESTIMATION   OF   PHOSPHORIC   ACID.  701 

two  hours,  is  collected  on  a  filter  and  washed  with  water 
containing  ammonia,  as  pure  water  decomposes  it.  It  is  then 
dried  and  ignited,  whereby  it  is  converted  into  pyrophosphate 
of  magnesia,  2MgO.P05,  containing  63*67  per  cent,  of 
phosphoric  acid,  POg,  and  27*98  per  cent,  of  phosphorus. 

If  the  phosphoric  acid  is  in  the  monobasic  or  bibasic  modi- 
fication, it  must  first  be  converted  into  the  tribasic  acid  by 
fusing  the  salt  with  five  or  six  times  its  weight  of  carbonate 
of  soda,  or,  better,  with  a  mixture  of  carbonate  of  potash  and 
carbonate  of  soda  in  equivalent  proportions.  The  mixture 
may  then  be  fused  over  a  lamp,  whereas  if  carbonate  of  soda 
or  carbonate  of  potash  alone  be  used,  the  heat  of  a  furnace 
will  be  required.  By  this  fusion  with  excess  of  an  alkaline 
carbonate,  the  phosphoric  acid  is  in  most  cases  completely 
separated  from  any  other  base  with  which  it  may  be  combined, 
and  converted  into  a  tribasic  phosphate  of  the  alkali,  which 
may  then  be  treated  as  above. 

Phosphates  which  are  insoluble  in  water,  may  be  dissolved 
in  nitric  or  hydrochloric  acid ;  and  from  these  solutions,  the 
bases  may  in  some  cases  be  precipitated  by  hydrosulphuric 
acid,  in  others  by  sulphide  of  ammonium,  and  the  phosphoric 
acid  subsequently  precipitated  from  the  filtered  solution  in  the 
form  of  the  ammonio-magnesian  phosphate  in  the  manner  above 
described. 

To  separate  phosphoric  acid  from  the  earths,  other  methods 
are  required.  From  baryta  it  is  easily  separated  by  sulphuric 
acid,  which  throws  down  the  baryta ;  from  strontia  and  lime, 
also,  by  sulphuric  acid  with  addition  of  alcohol.  From  mag- 
nesia  it  may  be  separated  by  fusion  with  a  mixture  of  carbon- 
ate of  potash  and  carbonate  of  soda  in  equivalent  proportions. 
From  alumina  it  is  most  readily  separated  by  dissolving  the 
compound  in  hydrochloric  acid,  adding  sufficient  tartaric  acid 
to  keep  the  alumina  in  solution  when  the  liquid  is  neutralised 
by  an  alkali,  and  then  adding  excess  of  ammonia  and  sulphate 
of  magnesia,  whereby  a  precipitate  of  ammonio-magnesian 


702  CHLORINE. 

phosphate  is  produced,  which  may  be  treated  as  already 
described.  This  method  may  also  be  applied  to  the  separation 
of  phosphoric  acid  from  iron. 

When  phosphoric  acid  exists  in  combination  with  several 
earthy  bases  together,  it  may  be  separated  by  dissolving  the 
compound  in  nitric  acid,  adding  metallic  mercury  in  slight 
excess,  evaporating  over  the  water-bath  to  perfect  dryness, 
and  treating  the  residue  with  water.  The  whole  of  the  phos- 
phoric acid  then  remains  undissolved  in  the  form  of  mercurous 
phosphate,  while  the  bases  pass  into  the  solution  as  nitrates. 
(H.  Rose.)  This  method,  however,  requires  attention  to  a 
number  of  details  and  precautions  which  cannot  here  be 
given. 

Another  method  of  separating  phosphoric  acid  from  a  mix- 
ture of  bases,  by  means  of  acetate  of  uranium,  has  already 
been  described  (II.  258). 

The  salts  of  phosphorous  and  hypophosphorous  acid  may  be 
oxidised  by  nitric  acid,  the  former  being  thereby  converted 
into  pyrophosphates,  the  latter  into  metaphosphates.  These 
salts  must  then  be  converted  into  tribasic  phosphates  in  the 
manner  above  described. 

Phosphorous  and  hypophosphorous  acid  may  also  be  esti- 
mated by  their  power  of  precipitating  gold  in  the  metallic  state 
from  its  solutions,  or,  better,  by  their  reducing  action  on  mer- 
curic chloride,  which,  when  present  in  excess,  is  reduced 
to  mercurous  chloride. 


CHLORINE. 

Chloride  of  Nitrogen  (I.  481). — According  to  Bineau  *,  this 
compound  is  NCI3,  that  is  to  say,  ammonia  in  which  all  the 
hydrogen  is  replaced  by  chlorine.  Bineau's  analysis  gives 
10*6  p.c.  N,  and  89*3  CI;  the  formula  requires  11 -65  N,  and 

♦  Ann.  Ch.  Phys.  [3],  xv.  71. 


SULPHITE  OP  PERCHLORIDE  OF  CARBON.     703 

88*35  CI.  According  to  Porrett,  Wilson,  and  Kirk*,  it 
is  NHCI3;  according  to  Gladstone  f,  N2HCI5,  or  NHClg 
+  NCI3. 

Sulphite  of  Perchloride  of  Carbon,  CJCI4.2SO2. — This  body 
was  discovered  by  Berzelius  and  Marcet,  who  obtained  it  by 
the  action  of  aqua-regia  on  bisulphide  of  carbon ;  but  a  better 
mode  of  obtaining  it  is  the  following :  —  A  bottle,  capable  of 
holding  about  three  pints,  is  half  filled  with  a  mixture  of  per- 
oxide of  manganese  and  hydrochloric  acid ;  about  800  grains 
of  bisulphide  of  carbon  are  then  added ;  the  vessel  quickly 
closed,  and  left  for  some  days  in  a  cool  place.  It  is  then  ex- 
posed for  several  days  longer  to  a  temperature  of  30°  C. 
(86°  F.),  or  in  summer  to  direct  sunshine,  and  frequently 
shaken,  till  the  greater  part  of  the  bisulphide  of  carbon  is 
converted  into  the  new  compound.  The  action  may  be 
greatly  accelerated  by  adding  a  quantity  of  nitric  acid 
equal  in  weight  to  twice  that  of  the  bisulphide  of  car- 
bon used.  The  mixture  is  then  distilled,  whereupon  un- 
decomposed  bisulphide  of  carbon  first  passes  over,  toge- 
ther with  chloride  of  sulphur  and  a  peculiar  yellow  liquid 
(C4S4CI4),  and  afterwards  the  sulphite  of  perchloride  of 
carbon  condenses  in  the  solid  form  in  the  neck  of  the  retort. 
The  formation  of  this  compound  is  represented  by  the  follow- 
ing equation : 

2CS2  +  8Cl  +  4H0  =  C2CI4.2SO2  +  4HC1  +  2S. 

Sulphite  of  perchloride  of  carbon  is  a  white  crystalline 
solid  having  a  highly  pungent  odour,  and  exciting  tears.  It 
melts  at  135°  C.  and  boils  at  170°;  maybe  sublimed,  and 
forms  small  rhombohedral  crystals.  It  is  soluble  in  alcohol, 
ether,  and  bisulphide  of  carbon ;  insoluble  in  water.  It  is 
decomposed  at  a  dull  red  heat,  yielding  chlorine,  sulphurous 
acid,  and  protochloride  of  carbon :  — 

*  Gmelin's  Handbook,  ii,  472.  f  Chem.  Soc.  Qu.  J.  vii.  51. 


704  CHLORINE. 

2(C2Cl4 .  2SO2)  =  4C1  +  4SO2  +  2C2CI2. 

It  decomposes  slowly  in  contact  with  water  or  moist  air, 
yielding  sulphurous,  sulphuric,  carbonic,  and  hydrochloric 
acids.  Heated  with  a  large  excess  of  strong  sulphuric  acid, 
it  gives  off  sulphurous  acid,  anhydrous  sulphuric  acid,  hydro- 
chloric acid,  and  phosgene  gas  :  — 
C2CI4 .  2SO2  +  2SO4H  =  2SO2  +  2SO3  +  2HC1  +  2C0C1.* 

ChlorosuIpMde  of  Carbon  C4S4CI4.  —  The  liquid  distillate 
obtained  in  the  preparation  of  the  preceding  compound  con- 
tains this  substance,  which  may  be  obtained  from  it  in  a  state 
of  purity  by  repeated  distillation  with  water  and  hydrate  of 
magnesia,  which  decomposes  the  chloride  of  sulphur.  It  may 
also  be  prepared  by  exposing  bisulphide  of  carbon  to  sun- 
shine in  an  atmosphere  of  dry  chlorine — 

CS2  +  2C1  =  SCI  +  CSCl, 

and  purified  as  above.  Also  by  passing  a  mixture  of  hydro- 
sulphuric  acid  gas  and  vapour  of  perchloride  of  carbon 
through  a  red-hot  tube  :  — 

2C2CI4  +  4HS  =  4HC1  +  C4S4CI4. 

It  is  a  yellow  liquid,  not  miscible  with  water ;  has  a  peculiar 
and  powerful  odour,  and  irritates  the  eyes  very  strongly  ; 
Sp.  gr.  1-46.  It  boils  at  70°  C.  (158°  F.).  It  is  not  decomposed 
by  water  or  acids,  not  even  by  nitric  acid.  Bisulphide  of 
carbon  and  caustic  potash  decompose  it  gradually.  It  absorbs 
ammoniacal  gas  (Kolbef). 

Sulphite  of  Protochloride  of  Carbon,  C2CI2.2SO2. — Formed 
by  the  action  of  reducing  agents,  viz.,  sulphurous  acid, 
hydro-sulphuric  acid,  zinc,  iron,  pro  to-chloride  of  tin,  &c., 
on  the  sulphite  of  perchloride  of  carbon.  It  has  not  been 
obtained  in  the  anhydrous  state.  It  dissolves  in  water 
and   alcohol,   and   is   best   prepared   in    the   state   of    solu- 

♦  Kolbc,  Ann.  Ch.  Thaim.  liv.  148.  f  I^'^^-  ^1^'-  ^3. 


CHLOROMETHYLOSULPHUROUS   ACID.  705 

tion,  by  passing  sulphurous  acid  gas  through  an  alcoholic 
solution  of  sulphite  of  perchloride  of  carbon.  The  solution 
is  colourless  and  inodorous,  has  an  acid  reaction,  ?nd  absorbs 
oxygen  rapidly,  forming  sulphuric  acid  and  phosgene  :  — 

C2CI2.2SO2  +  40  =  2SO3  +  2C0C1. 

Chlorine  converts  it  into  C2CI4 .  2SO2.     (Kolbe.) 

Perchlorocarbosulphurous  acid,  CgClgO .  2SO2 .  HO. — Formed 
by  the  action  of  caustic  alkalies  on  sulphite  of  perchloride 
of  carbon: — 

C2CI4.2SO2  4-  2K0  =  C2Cl3O.2SO2.KO  +  KCl. 

The  hydrated  acid  is  obtained  by  decomposing  the  baryta- 
salt  with  sulphuric  acid.  It  crystallises  in  small  deliquescent 
prisms,  which  may  be  partially  sublimed  without  decomposi- 
tion. They  contain  2  at.  water  of  crystallisation,  their  for- 
mula being  C2Cl30.2SO^.HO  +  2H0.  The  acid  is  not 
decomposed  by  fuming  nitric  acid  or  aqua-regia,  and  is  so 
powerful  an  acid  that  it  expels  hydrochloric  acid  from  its  com- 
binations. Its  salts  are  all  soluble  in  water  and  alcohol,  and 
crystallise  with  facility.  When  heated  they  are  resolved 
into  phosgene,  sulphurous  acid,  and  a  metallic  chloride ;  e.  g. 

C,Cl30.2S03.KO  =  2C0C1  +  2SO2  +  KCl. 

Chlorocarbosulpkurous  acid,  C2CI2. 2 SOg .  2H0.  —  Formed 
by  the  action  of  alkalies  on  sulphite  of  protochloride  of  car- 
bon, or  by  the  action  of  zinc  on  the  preceding  acid.  Resem- 
bles the  preceding  in  most  of  its  properties.  Its  salts,  when 
heated,  give  off  phosgene,  sulphurous  acid,  and  water,  and 
leave  a  residue  of  metallic  chloride  and  charcoal. 

Chloromeiliylosulphurous  acid,  CgHCl .  2SO2 .  2H0.— Formed 
by  the  continued  action  of  nascent  hydrogen  on  chlorocarbo- 
sulphurous  acid :  — 

CaCl2.2SO2.2HO  +  H  =  C2HCI.2S02.2HO  +  HCl. 


706  CHLORINE. 

When  zinc  is  immersed  in  an  aqueous  solution  of  clilorocarbo- 
sulphurous  acid,  it  dissolves  with  evolution  of  liydrogen  ;  and 
the  hydrogen,  as  it  is  set  free,  converts  part  of  the  acid  into 
chloromethylosulphurous  acid ;  but  complete  transformation 
can  only  be  obtained  by  subjecting  an  acidulated  solution  of  a 
perchlorocarbosulphite  or  chlorocarbosulphite  to  the  action  of 
the  galvanic  current.  The  hydrated  acid  is  a  viscid,  strongly 
acid  liquid,  w^hich  bears  a  heat  of  140°  C.  v^^ithout  decompo- 
sition ;  at  —16*6°  C.  it  becomes  syrupy  ;  in  other  respects  it 
resembles  perchlorocarbosulphurous  acid.  All  its  salts  are 
soluble  in  water,  and  crystallisable. 

Methylosulphurous  acid,  C2H3O .  2 SOg .  HO.  — Formed  when 
a  neutral  solution  of  perchlorocarbosulphite  of  potash  is  decom- 
posed by  the  electric  current,  the  electrodes  being  formed  of 
amalgamated  zinc  plates :  — 

C2Cl3O.2SO2.KO    +    6Zn   +   6H0  =  C2H3O.2SO2.KO 
+  6ZnO  +  3HC1. 

Also  when  an  amalgam  of  potassium  is  immersed  in  the  same 
solution, 

C2Cl3O.2SO2.KO  -f   6K  +  3H0  =  C2H3O.2SO2.KO 
-f    3KCI  -f   3K0. 

The  concentrated  solution  of  the  hydrated  acid  is  a  sour,  ino- 
dorous, viscid  liquid,  which  may  be  heated  to  nearly  130°  C. 
without  decomposition,  but  at  that  temperature  begins  to 
turn  brown  and  decompose.  It  does  not  crystallise  when 
pure.  It  is  equal  to  perchlorocarbosulphurous  acid  in  stabi- 
lity and  in  affinity  for  bases.  Its  salts  are  soluble  and  crys- 
tallisable.    (Kolbe.*) 

Intermediate  Chloride  of  Sulphur,  S4CI3.  —  Protochloride  of 
sulphur  is  readily  decomposed  by  heat,  its  boiling  point  rising 
quickly  from  64°  to  78°  C,  where   it   remains    stationary. 

♦  Ann.  Ch.  Tharm.  liv.  143. 


CHLORIDES   OF   SULPHUR.  707 

The  deep  orange-yellow  liquid  thus  obtained  appears  to  be 
composed  of  S4CI3  =  Sfil  +  2SCI. 

Terchloride  of  Sulphur,  SCI3.  —  Not  known  in  the  separate 
state,  but  exists  in  the  compound  SCI3 .  5SO3,  obtained  by 
mixing  the  protochloride  of  sulphur,  SCI,  with  Nordhausen 
sulphuric  acid,  and  distilling.  Sulphurous  acid  and  anhydrous 
sulphuric  acid  pass  over  first,  then  the  compound  SCI3  .  5SO3, 
while  monohydrated  sulphuric  acid  remains  in  the  retort. 
The  compound  SCI3 .  5SO3  is  a  colourless  oily  liquid  having 
a  peculiar  odour,  and  fuming  slightly  in  the  air.  Its  density 
is  1*818,  and  that  of  its  vapour  4*481.  Boils  at  145°  C. 
(283°  F.).  Water  decomposes  it  rapidly,  forming  sulphuric 
and  hydrochloric  acids.     (H.  Rose.) 

Chlorosulphuric  acid,  SO^Cl,  is  regarded  by  some  chemists 
as  a  bisulphate  of  terchloride  of  sulphur,  SCI3. 2SO3.* 

Sulphate  of  Bichloride  of  Sulphur,  SCI2.SO3  =  S2CI2O3. 
—Formed  by  the  action  of  moist  chlorine  gas  on  protochloride 
of  sulphur.  Large  transparent  colourless  crystals,  which  are 
decomposed  by  alcohol  and  water,  or  even  by  exposure  to 
damp  air.  Enclosed  in  a  sealed  glass  tube,  they  change  in 
the  course  of  a  few  months  into  a  very  mobile,  slightly 
yellow  liquid,  which  has  the  same  composition  as  the  crystals, 
but  does  not  solidify  at  —18°  C.  (0°  F.),  It  is  dissolved  by 
water,  with  formation  of  sulphuric  and  hydrochloric  acids. 
The  compound  S2CI2O3  may  be  regarded  as  hyposulphuric 
acid  in  which  2  at.  O  are  replaced  by  chlorine.     (Millon.f) 

Chlorosulphide  of  Phosphorus,  PSjoCl^. — Besides  the  chlo- 
rosulphide  of  phosphorus  described  on  page  487,  Yol.  I., 
another  compound  of  these  elements,  having  the  formula 
just  given,  is  obtained  by  passing  a  stream  of  phosphuretted 
hydrogen  into  di chloride  of  sulphur.  This  compound  is  a 
yellow  syrupy  liquid,  which  is  decomposed  by  water,  with 

*  See  Vol.  I.,  page  411,  line  4,  where,  however,  there  is  a  misprint,  the 
formula  being  given  as  3SO3.SCI3  instead  of  2SO3.SCI3. 
t  Ann.  Ch.  Fharm.  lii.  230;  Ixxvi.  235. 


708  CHLORINE. 

evolution  of  hjdrosulphuric  acid  and  deposition  of  sulphur.  It 
may  be  regarded  as  a  compound  of  dichloride  of  sulphur  with 
a  peculiar  sulphide  of  phosphorus,  not  yet  isolated : — 

48^01  +  PS2  =  PS10CI4. 
This  compound  was  discovered  by  H.  Rose. 

Sulphide  of  Pentachloride  of  Phosphorus,  PCI5.S4. — When  a 
mixture  of  3  pts.  pentachloride  of  phosphorus  and  1  pt.  of 
sulphur  is  melted,  a  colourless  liquid  is  obtained,  which  boils 
at  about  100°  C.  It  dissolves  large  quantities  of  pentachloride 
of  phosphorus  and  sulphur,  the  latter  of  which  it  deposits  in 
crystals ;  it  is  very  difficult  to  purify.  Water  decomposes  it 
immediately,  with  formation  of  a  great  number  of  products 
(Gladstone.*)  The  compound  may  be  regarded  as  PS2CI3 
4-  CI2S2  (SchifFf). 

Action  of  acids  on  Pentachloride  of  Phosphorus.  —  Persoz 
and  Bloch  J,  by  passing  dry  sulphurous  acid  gas  over  penta- 
chloride of  phosphorus,  obtained  a  volatile,  strongly  refracting 
liquid  which  they  regarded  as  PCI5.  2SO2.  According  to 
SchifF§,  however,  this  liquid  is  decomposed  by  fractional 
distillation,  being  resolved  into  oxychloride  of  phosphorus 
which  boils  at  110°  C.  (230  F.),  and  a  more  volatile  liquid, 
which  passes  over  at  82°  C.  (147*6  F.).  This  latter  is  the 
chloride  of  thionyl,  ^fi^.  •  ^^2'  ^^^  name  thionyl  denoting  the 
biatomic  radical,  SgOg,  of  sulphurous  acid  and  its  salts,  hy- 

S  O  ) 
drated  sulphurous  acid  being  '^xi^fO^,  and  anhydrous  sul- 
phurous acid  SjjOg.Og.  Chloride  of  thionyl  is  a  volatile  liquid 
of  great  refracting  power,  and  having  a  suffocating  odour  like 
that  of  sulphurous  acid.  It  is  decomposed  by  water,  and 
more  readily  by  alkalies,  into  hydrochloric  and  sulphurous 
acids.  With  alcohol,  it  yields  hydrochloric  and  ethylosul- 
phurous  acids. 

*  Chem.  Soc.  Qu.  J.  iii.  5.  f  Ann.  Ch.  Pharm.  ci.  309. 

%  Compt.  rend,  xxvii.  86.  §  Ann.  Ch  Pharm.  cii.  111. 


ACTION   OF   ACIDS   ON   PCI5.  709 

(SO 
Thiona7nide,  Ng  ]    K  ^,  is  produced  when  chloride  of  thionyl 

is  brought  in  contact  with  dry  ammonia : 

S2O2 .  CI2  +  4NH3  =  2NH,C1  +  N2(S202)H,. 

The  action  is  very  violent,  but  may  be  moderated  by  cooling. 
The  product  is  a  white,  non-crystalline  solid,  which  gives  up 
sal  ammoniac  when  digested  in  water,  and  is  afterwards  com- 
pletely decomposed. 

Anhydrous  sulphunc  acid  acts  upon  pentachloride  of 
phosphorus  in  the  same  manner  as  anhydrous  sulphurous 
acid,  producing  a  liquid  which  Persoz  and  Bloch  regarded  as 
PCI5 .  2SO3,  but  which,  according  to  SchifF,  is  resolved  by- 
distillation  into  oxychloride  of  phosphorus,  and  chloride  of 
sulphuryl  or  chlorosulphuric  acid,  SgO^  .  C\, 

With  hydrated  sulphuric  acid,  pentachloride  of  phosphorus 
forms  chlorohydrated  sulphuric  acid,  SgHClOg  : 

¥;|^4  +  PCI,  =  l^gfjO,  +  HCl  +  PO.Cl,. 

And  this  compound,  by  the  further  action  of  the  pentachloride, 
is  converted  into  chlorosulphuric  acid,  S204.Cl2(p.  551). 
Chlorohydrated  sulphuric  acid  is  a  liquid  which  boils  at 
145°  C,  is  decomposed  by  water,  yielding  hydrochloric  and 
sulphuric  acids,  and  dissolves  chloride  of  sodium  at  a  gentle 
heat,  with  evolution  of  hydrochloric  acid  and  formation  of 
the  compound  SgNaClOg.  It  effervesces  with  melted  nitre, 
giving  off  a  vapour  (probably  NO4CI)  which  smells  like  aqua- 
regia,and  when  passed  into  water,  forms  nitric  and  hydrochloric 
acids.  The  compound  SgHClOg  is  probably  identical  with 
that  which  H.  Rose  obtained  by  the  action  of  sulphuric  acid 
on  pentachloride  of  sulphur,  and  regarded  as  SgOgCl.  It  is 
likewise  obtained  in  small  quantity  by  the  action  of  strongly- 
heated  platinum-black  on  an  imperfectly  dried  mixture  of 
chlorine  and  sulphurous  acid.     (Williamson.*) 

»  Proceedings  of  the  Royal  Society,  vii.  11. 
VOL.  II.  3  C 


710  CHLORINE. 

Tungstic  acid  treated  with  pentachloride  of  phosphorus 
yields  oxychloride  of  phosphorus  and  an  oxychloride  of 
tungsten,  WgO^Clg.     Similarly  with  molybdic  acid. 

Hydrated  antimonic  acid  heated  with  pentachloride  of  phos- 
phorus yields  hydrochloric  acid  and  oxychloride  of  phos- 
phorus, with  a  residue  of  anhydrous  antimonic  acid. 

Anhydrous  phosphoric  acid  and  pentachloride  of  phosphorus 
form  oxychloride  of  phosphorus : 

P,0,„  +  3P0],  =  5PO,Cl3. 

When  strong  nitric  acid'is  cautiously  added  to  pentachloride 
of  phosphorus,  hydrochloric  acid  is  evolved;  and  if  the 
escaping  vapour  be  passed  through  a  good  refrigerating 
apparatus,  a  blood-red  liquid  condenses,  which  when  distilled 
yields  yellowish-red  vapours,  probably  NO^Cl,  and  a  distillate 
of  oxychloride  of  phosphorus.     (Schiff.) 

Chlorophosphide  of  Nitrogen,  PgNgCl^  according  to  Wohler 
and  Liebig,  who  discovered  it;  P3N2CI3  according  to 
Gladstone;  PNCI2  according  to  Laurent.  It  is  formed  by 
the  action  of  ammonia  on  pentachloride  of  phosphorus.  On 
treating  the  crude  product  with  ether,  the  chlorophosphide  of 
nitrogen  is  alone  dissolved,  and  may  then  be  crystallised.  It 
is  also  produced  by  distilling  a  mixture  of  1  pt.  pentachloride 
of  phosphorus  with  2  pts.  sal-ammoniac.  It  may  be  purified 
by  distillation  with  water,  being  carried  over  by  the  vapour 
of  water,  and  then  only  requires  to  be  dried.  It  crystallises  in 
rhomboidal  prisms;  melts  at  110°,  and  boils  at  240°  C. 
It  is  insoluble  in  water,  but  dissolves  in  alcohol,  ether,  and 
oil  of  turpentine.  Alkalies  decompose  it,  with  formation  of 
phosphamic  acid  (p.  699). 


SULPHOBROMIDE  OF  PHOSPHORUS.        711 


BROMINE. 

JBromide  of  Nitrogen,  —  When  chloride  of  nitrogen  is 
gently  heated  with  bromide  of  potassium,  double  decomposition 
takes  place,  and  a  brown,  very  heavy,  oily  liquid  is  formed, 
which  appears  to  be  bromide  of  nitrogen.  It  is  very  volatile, 
has  an  offensive  odour,  and  irritates  the  eyes  strongly.  It 
detonates  easily,  and  is  decomposed  by  hydrochloric  acid, 
hydrobromic  acid,  and  ammonia.  Its  composition  appears  to 
be  NBrg.     (Millon.) 

Oxyhromide  of  Phosphorus,  PBrgOg.  —  Produced  by  the 
decomposition  of  the  pentabromide  in  moist  air.  When  the 
thick  reddish  liquid  thus  formed  is  heated,  to  drive  off  the 
hydrobromic  acid  which  it  contains,  and  then  distilled  at 
about  180°  C.  (366°  F.),  the  oxybromide  passes  over  in  the  form 
of  a  colourless  heavy  liquid,  which  boils  between  170°  and 
200°  C.  It  does  not  mix  with  water,  but  is  slowly  decomposed 
by  that  liquid,  with  formation  of  phosphoric  and  hydrobromic 
acids.  It  dissolves  in  oil  of  turpentine,  ether,  and  strong 
sulphuric  acid,  and  is  precipitated  from  the  last-mentioned 
solution  by  water.  Nitric  acid  decomposes  it,  with  evolution 
of  bromine.  Another  body,  apparently  of  the  same  compo- 
sition, but  solid  and  crystalline,  is  sometimes  obtained  as  a 
residue  in  the  distillation  of  pentabromide  or  oxybromide  of 
phosphorus,  and  by  the  action  of  moist  air  on  the  pentabromide 
in  an  imperfectly-closed  vessel.  It  is  decomposed  by  water, 
melts  and  volatilises  when  heated,  but  on  cooling  remains 
as  a  liquid,  exhibiting  the  characters  of  the  oxybromide. 
(Gladstone.*) 

Sulphobromide  of  Phosphorus.  —  Pentabromide  of  phos- 
phorus is  decomposed  by  hydrosulphuric  acid,  with  formation 
of  a  heavy  liquid,  which  boils  without  decomposition  at 
200°  C,  and  appears  to  have  the  composition  SPBrg  .  PS3  ;  it 

*  Phil.  Mag.  [3J,  xxxv.  .345. 
3  c  2 


712  IODINE. 


may,  however,  be  a  mixture  of  two  compounds  having  nearly 
the  same  boiling  point.     (Gladstone.*) 


IODINE. 

Natural  sources  of  Iodine. — According  to  Chatin  f,  iodine 
exists  in  the  air,  in  nearly  all  water,  and  in  a  great  number  of 
plants,  land  and  fresh-water  as  well  as  marine ;  also  in  coal, 
in  various  chemical  products,  viz.,  commercial  potash,  soda, 
and  sal-ammoniac,  in  wine,  cider,  perry,  &c.,  in  milk  and 
eggs.  He  finds  also  that  iodine  is  least  abundant  in  the  air 
and  water  of  those  localities  in  which  goitre  and  cretinism 
prevail.  Similar  results  have  been  obtained  by  other  che- 
mists. On  the  other  hand.  Macadam  J,  Lomeyer  §,  and  others 
have  not  been  able  to  detect  iodine  in  the  air  or  in  rain-water. 
Macadam,  however,  found  iodine  in  commercial  potash,  in 
numerous  samples  of  alkaline  carbonates  (used  as  reagents), 
in  the  ashes  of  wood-charcoal,  in  coal,  and  in  numerous 
plants.  Lomeyer  examined  particularly  the  air  and  water  of 
various  localities  where  goitre  is  scarce,  but  found  no  trace  of 
iodine.  Chatin  ||  attributes  the  negative  results  obtained  by 
Macadam  and  Lomeyer  to  defective  methods  of  analysis,  but 
does  not  give  any  exact  description  of  his  own  process. 

Hypoiodic  acid,  IO4,  and  Suh-hypoiodic  acid,  I5O19  =  4IO3  + 
lOy.  —  When  one  part  of  iodic  acid  and  5  parts  of  monohy- 
drated  sulphuric  acid  are  heated  in  a  platinum  crucible,  till 
oxygen  gas  and  afterwards  vapours  of  iodine  are  evolved,  a 
green  solution  is  obtained ;  and  on  leaving  this  for  some  days 
in  a  dry  atmosphere,  a  yellow  crystalline  crust  is  deposited, 
which,  when  freed  from  the  excess  of  sulphuric  acid  and 
washed  with  water  and  alcohol,  yields  sub-hypoiodic  acid  ;  and 
this  compound  heated  to  150°  C.  gives  off  vapour  of  iodine,  and 

*  Phil.  Mag.  [3],  XXXV.  345. 

t  Compt.  rend.  xxx.  352  ;  xxxi.  380  ;  xxxii.  669  ;  xxxiii.  519,  529,  581. 
%  Chcm.  Soc.  Qu,  J.  vi.  166.  §  Phil.  Mag.  [4],  vi.  237. 

II  J.  Pharm.  [3],  xxv.  192. 


IODIDE   OF   NITROGEN.  713 

is  converted  into  hypoiodic  acid.  The  latter  is  a  sulphur- 
yellow  amorphous  powder,  which  at  180°  C.  is  resolved  into 
iodic  acid  and  iodine.  Water  and  nitric  acid  decompose  it 
in  a  similar  manner.  Sulphuric  acid  dissolves  it  with  the  aid 
of  heat,  and  on  cooling  deposits  a  compound  consisting  of 
IO4.4SHO4.  Aqueous  alkalies  decompose  hypoiodic  acid, 
forming  iodates  and  the  other  compounds  which  result  from 
the  action  of  iodine  on  alkalies. 

Sub-hypoiodic  acid  bears  a  considerable  resemblance  to 
hypoiodic  acid,  both  in  physical  and  chemical  properties. 
When  heated,  it  gives  off  iodine  and  leaves  hypoiodic  acid. 
(Millon.) 

Iodide  of  Nitrogen  (I.  501). — Gladstone*  has  analysed  this 
compound  (as  prepared  by  precipitating  an  alcoholic  solution 
of  iodine  with  excess  of  ammonia  and  washing  with  water), 
and  arrived  at  results  which  accord  with  Bineau's  formula, 
NHT2.  By  decomposing  the  compound  with  hydrosulphuric 
acid,  he  finds  that  it  contains  21  to  IN,  while  its  decompo- 
sition by  aqueous  sulphurous  acid  agrees  with  the  equation, 

NHI2  +  4SO2  +  4H0  =   NH3  +    2HI   +   4SO3. 

Gladstone  suggests  for  the  compound  the  name  iodimide.  He 
also  finds  the  above  formula  to  be  in  accordance  with  the 
formation  of  the  compound  by  the  action  of  hypochlorite  of 
lime  on  iodide  of  ammonium  (observed  by  Playfair),  that 
reaction  being  attended  with  evolution  of  ammonia,  according 
to  the  equation, 

2(CaO.G10)  +  2NHJ  =  NHI^  +   2  CaCl   +  4  HO  + 

NH3. 

Bunsen  takes  a  different  view  of  the  constitution  of  iodide 
of  nitroi^en.  He  observes  :  1.  That  the  mode  of  formation 
of  this  compound  from  iodine  and  ammonia,  with  hydriodic 
acid  as  the  only  secondary  product,  shows  that  it  must  be  a 

*  Chctn.  Soc.  Qu.  J.  v.  34. 
3  c  3 


714  IODINE, 

substitution-product  of  ammonia,  of  the  form  NI3,  NHIg  or 
NHgl,  associated  at  most  with  ammonia  or  hydriodic  acid ; 
2.  That  it  cannot  contain  hydriodic  acid,  because  it  dissolves 
in  hydrochloric  acid  without  evolution  of  gas,  and  forms  a 
solution  containing  ammonia  and  protochloride  of  iodine,  but 
no  hydriodic  acid ;  3.  That,  to  determine  its  composition,  it 
is  sufficient  to  ascertain  how  much  ICI  and  how  much  NH3 
it  yields  with  hydrochloric  acid,  and  to  see  which  of  the 
following  equations  agrees  with  the  results  : 

(a)  NI3   4-   3HC1   =    3ICI   +   NH3. 

(b)  NHI2   +   2HC1   =   2IC1   +   NH3. 

(c)  NHJ   -f   HCl  =   ICI   +   NH3. 

.     (d)  NHJ   +   NH3   +   HCl  =   ICI   +    2  NH3,  &c. 

Preparations  obtained  by  mixing  cold  and  more  or  less 
saturated  anhydrous  alcoholic  solutions  of  iodine  and  am- 
monia, which  were  not  decomposed  by  washing  with  absolute 
alcohol,  gave,  when  dissolved  in  hydrochloric  acid,  quantities 
of  ammonia,  iodine,  and  chlorine,  in  the  atomic  proportion 
of  2  :  3  :  3,  showing  that  the  constitution  of  the  compound  is 
NI3  +  NH3.  A  preparation  obtained  by  adding  ammonia  to 
a  solution  of  iodine  in  aqua-regia  diluted  with  water,  and 
washed  as  quickly  as  possible  with  cold  water,  gave,  with 
hydrochloric  acid,  quantities  of  ammonia  and  protochloride 
of  iodine  in  the  atomic  proportion  of  5  :  12,  showing  that  its 
formula  was  4NI3  +  NHg.  When  washed  with  water  for 
any  length  of  time,  even  till  the  greater  part  of  the  compound 
was  decomposed,  with  separation  of  iodine  and  nitrogen,  the 
undecomposed  portion  still  yielded  more  than  1  at.  ammonia 
to  3  at.  chloride  of  iodine,  a  proof  that  ammonia  enters  es- 
sentially into  its  constitution.  Bunsen  is  of  opinion  that 
there  exist  two  distinct  compounds,  NI3  .  NH3  and  4NI3 .  NH3, 
formed  in  the  manner  shown  by  the  equations, 

2NH3   +    61   =   (Nl3.NIi3)   +    3III; 
4(Nl3 .  NH3)  -t  3H0  =  4Nr3  .  NH3  -f  3NII,0. 


IODIDES   OP   PHOSPHORUS.  715 

The  formation  of  the  so-called  iodide  of  nitrogen  by  the 
action  of  ammonia  on  a  solution  of  iodine  in  aqua-regia,  would 
be  inconsistent  with  this  view,  if  that  solution  contained, 
not  ICl,  but,  as  is  commonly  supposed,  ICI3,  because  NI3 
could  not  be  formed  by  the  action  of  ammonia  upon  the  latter. 
Experiment,  however,  shows  that  the  solution  of  iodine  in 
aqua-regia  contains  only  ICl.  The  formation  of  the  so-called 
iodide  of  nitrogen  from  ICl  is  explained  by  the  equation, 

2NH3  +  3IC1  =  (NI3  .  NH3)  +  3HC1. 
The  immediate  products  of  its  explosion  are  nitrogen  and 
hydriodic  acid :  • 

NI3  .  NH3  =  2N  +  SHI, 

which  latter  is  for  the  most  part  resolved  by  the  high  temper- 
ature into  iodine  and  hydrogen,  while  another  portion  unites 
with  the  ammonia  of  the  compound,  forming  iodide  of  ammo- 
nium, thereby  setting  free  quantities  of  iodine  and  nitrogen 
equivalent  to  this  ammonia.* 

Gladstone,  in  a  subsequent  communication  f,  remarks  that 
his  mode  of  preparing  the  iodide  of  nitrogen  differs  essentially 
from  that  of  Bunsen,  and  that  his  formula  NHIg  may  be 
written  2NI3  +  NII3,  which  shows  it  to  be  intermediate 
between  the  two  formulae  given  by  Bunsen.  He  concludes, 
from  further  experiments,  that  the  formula  NHIg  is  true,  not 
only  for  the  preparation  obtained  by  the  method  described  in 
his  former  paper,  but  likewise  for  that  obtained  by  preci- 
pitation from  solutions  of  iodine  and  ammonia  in  absolute 
alcohol. 

Iodides  of  Phosphorus  (I.  502). — These  compounds  are  best 
prepared  by  dissolving  iodine  and  phosphorus  together  in  bi- 
sulphide of  carbon,  and  cooling  the  solution  till  it  crystallises. 
There  appear  to  be  only  two  iodides  of  phosphorus,  viz.  Pig 
and  PI3,  which  are  prepared  by  dissolving  the  two  substances 
as  above,  in  the  respective  atomic  proportions  ;  if  they  be  mixed 

*  Chcm.  Soc.  Qu.  J.  vi.  90.  f  Ibid,  vii,  51. 

3  c  4 


716  IODINE. 

in  any  other  proportions,  the  same  compounds  crystallise  out, 
together  with  the  excess  of  iodine  or  phosphorus. 

The  biniodide,  Pig,  is  a  light- red  solid  body,  which  melts 
at  110°  C,  forming  a  red  liquid.  Water  decomposes  it,  with 
formation  of  hydriodic  and  phosphorous  acid,  and  deposition  of 
yellow  flakes.  When  melted  with  excess  of  phosphorus  and 
decomposed  by  water,  it  yields  red  phosphorus.  It  dissolves 
in  bisulphide  of  carbon,  and  is  deposited  from  the  solution  in 
flattened  prismatic  crystals,  of  a  light-orange  colour. 

The  teriodide,  PI3,  forms  dark-red  six-sided  laminae,  which 
dissolve  very  readily  in  bisulphide  of  carbon,  and  rapidly 
absorb  moisture  from  the  air.  It  melts  at  55°  C,  and  crystal- 
lises in  well-defined  prisms  on  cooling.  At  a  higher  tempera- 
ture, it  is  decomposed,  giving  off  vapours  of  iodine.  Water 
decomposes  it,  with  formation  of  hydriodic  and  phosphorous 
acids,  and  formation  of  an  orange-yellow  flaky  deposit. 
(Corenwinder.*) 

Estimation  and  separation  of  Chlorine,  Bromine,  andlodine. — 
Chlorine,  in  the  form  of  hydrochloric  acid  or  a  soluble  chloride, 
is  estimated  by  precipitation  with  nitrate  of  silver,  the  precipi- 
tate being  treated  in  the  manner  described  at  page  346.  The 
fused  chloride  contains  24*72  per  cent,  of  chlorine,  equivalent 
to  25*42  of  hydrochloric  acid. 

Many  chlorides,  chiefly  basic  or  oxychlorides,  which  are 
insoluble  in  water  dissolve  in  nitric  acid.  The  chlorine  in 
such  compounds  may  be  precipitated  by  adding  nitrate  of 
silver  to  the  nitric  acid  solution.  Care  must,  however,  be 
taken  not  to  heat  the  compound  with  excess  of  nitric  acid,  as 
in  that  case  a  portion  of  the  chlorine  may  be  lost.  Some 
chlorides,  as  the  chloride  of  silver  and  dichloride  of  mercury, 
are  insoluble  even  in  nitric  acid.  Chloride  of  silver  may 
be  decomposed,  either  by  ignition  in  a  current  of  hydrogen, 
by  heating  it  in  a  porcelain  crucible  with  a  mixture  of  the 

*  Ann.  Ch.  Phys.  [3],  xxx.  242. 


ESTIMATION   OF   CHLORINE,   BROMINE,  AND   IODINE.     717 

carbonates  of  potash  and  soda,  in  equivalent  proportions,  till 
the  salt  just  begins  to  melt,  or  by  treating  it  with  dilute  sul- 
phuric acid  in  contact  with  a  piece  of  pure  zinc  (p.  339).  Di- 
chloride  of  mercury  is  easily  decomposed  by  caustic  alkalies. 

Chlorates  and  other  oxygen- salts  of  chlorine  may  be  re- 
duced to  chlorides,  by  ignition,  or,  better  in  most  cases,  by 
the  action  of  sulphurous  or  hydrosulphuric  acid.  The  chlo- 
rine is  then  precipitated  by  nitrate  of  silver,  as  above,  after 
the  excess  of  the  reducing  agent  has  been  removed  by  means 
of  nitric  acid  or  a  ferric  salt.  [For  the  methods  of  deter- 
mining the  quantity  of  chlorine  in  bleaching  powder  and 
other  hypochlorites  for  commercial  purposes,  see  I.  592,  and 
II.  15;  also  Bunsen's  volumetric  method,  II.  722.] 

The  quantity  of  chlorine  in  an  organic  compound  is  deter- 
mined by  igniting  the  compound  with  excess  of  pure  quick 
lime  in  a  combustion -tube,  whereby  the  chlorine  is  converted 
into  chloride  of  calcium.  The  contents  of  the  tube  are  then 
dissolved  in  dilute  nitric  acid,  and  the  chlorine  precipitated  by 
nitrate  of  silver. 

Bromine  is  estimated  in  the  form  of  bromide  of  silver 
(containing  42*55  per  cent,  of  bromine),  in  exactly  the  same 
manner  as  chlorine.  Bromates  are  also  reduced  to  bromides 
in  the  same  manner  as  chlorates  to  chlorides. 

When  bromine  and  chlorine  occur  together,  they  may  both 
be  precipitated  by  treating  the  solution  with  excess  of  nitrate 
of  silver.  The  precipitate  of  chloride  and  bromide  is  then 
ignited  and  weighed ;  and  a  known  portion  of  it  is  afterwards 
heated  in  a  current  of  chlorine  gas.  The  bromide  of  silver 
is  thereby  converted  into  chloride,  the  bromine  passing  off  in 
vapour.  The  resulting  chloride  of  silver  weighs  less  than 
the  mixture  of  chloride  and  bromide  by  the  difference  (w) 
between  the  weight  of  the  bromine  which  has  escaped  and 
the  chlorine  which  has  taken  its  place ;  moreover,  these 
weights  are  to  one  another  as  the  equivalent  weights  of 
bromine  and  chlorine,  that  is,  as  80  to  35*5.     Hence,  to  deter- 


718  CHLORINE,    BROMINE,   AND   IODINE. 

mine  the  quantities  of  Br  and  CI  in  the  mixed  silver-salts, 
we  have  the  two  equations, 

Br~Cl  =  t.;     ^=     3^ 

whence  Br  =  1-8  zf;;     CI  =  0*8  w. 

If  the  quantity  of  bromine  is  very  small,  as  in  sea-water 
and  salt-springs,  in  comparison  with  that  of  the  chlorine,  this 
method  does  not  give  very  exact  results.  In  such  cases  it  is 
best  to  mix  the  solution,  after  due  concentration,  with  only 
enough  nitrate  of  silver  to  precipitate  about  one-sixth  of 
the  chlorine,  and  treat  the  precipitate  thus  formed, — which  is 
sure  to  contain  the  whole  of  the  bromine, — in  the  manner  just 
described.  The  remainder  of  the  chlorine  is  then  determined 
by  treating  the  filtered  liquid  with  excess  of  nitrate  of  silver. 

According  to  Mr.  F.  Field*,  chloride  of  silver  is  com- 
pletely decomposed  by  agitating  it  with  excess  of  bromide  of 
potassium  in  solution,  the  silver  being  converted  into  bromide, 
and  the  whole  of  the  chlorine  passing  into  the  solution.  This 
mode  of  decomposition  might  therefore  be  used  instead  of  the 
ignition  of  the  mixed  precipitate  in  a  current  of  chlorine. 
The  chloride  and  bromide  of  silver  are  also  completely  de- 
composed by  iodide  of  potassium. 

Iodine  in  soluble  iodides  is  estimated  by  precipitation  with 
nitrate  of  silver,  in  the  same  manner  as  chlorine  and  bromine  ; 
100  pts.  of  iodide  of  silver  contain  54*025  pts.  of  iodine. 

It  may  also  be  precipitated  as  iodide  of  palladium  by  mixing 
the  solution  with  nitrate  or  chloride  of  palladium.  A  black 
precipitate  then  falls,  which  settles  down  slowly  but  com- 
pletely, and  when  ignited,  leaves  metallic  palladium,  100  pts. 
of  which  are  equivalent  to  23*83  pts.  of  iodine ;  or  the  pre- 
cipitate may  be  collected  on  a  weighed  filter,  dried  at  100°  C. 
and  weighed;  100  pts.  of  it  contain  7*04  pts.  of  iodine :  but 
the  method  by  ignition  is  to  be  preferred. 

*  Chcm.  Soc.  Qn.  J.  x.  234. 


FLUORINE.  719 

This  method  of  precipitation  serves  also  to  separate  iodine 
from  bromine  and  chlorine.  If  the  chlorine  is  also  to  be  esti- 
mated, the  precipitation  must  of  course  be  made  with  nitrate 
of  palladium,  not  with  the  chloride.  If  bromine  is  present 
without  chlorine,  the  iodine  must  be  precipitated  with  chloride 
of  palladium,  because  the  nitrate  would  precipitate  bromine 
as  well  as  iodine  :  the  precipitation  of  the  bromine  may,  how- 
ever, be  prevented  by  the  addition  of  a  soluble  chloride.  To 
estimate  the  chlorine  and  bromine  in  the  filtered  liquid,  the 
excess  of  palladium  must  be  removed  by  hydrosulphuric  acid, 
and  the  excess  of  the  latter  by  means  of  nitric  acid  or  a  ferric 
salt.  The  bromine  and  chlorine  may  then  be  precipitated  by 
nitrate  of  silver,  and  the  precipitate  treated  in  the  manner 
already  described. 

The  methods  of  treating  insoluble  iodides  are  similar  to 
those  already  given  for  chlorides  (p.  716). 

lodates  and  periodates  are  reduced  to  iodides  by  the  action 
of  sulphurous  or  hydrosulphuric  acid.  To  decompose  them 
by  ignition  would  not  give  accurate  results,  because  a  portion 
of  the  iodine  is  thereby  expelled. 

Iodine  and  bromine  in  organic  compounds  are  estimated  in 
the  same  manner  as  chlorine  (p.  717). 


FLUORINE. 

Sources  of  Fluorine.  —  Professor  G.  Wilson,  of  Edinburgh, 
has  discovered  fluorine  in  a  great  number  of  plants,  especially  in 
the  siliceous  stems  of  grasses  and  equisetaceous  plants,  always 
however  in  very  small  and  variable  quantities.  He  supposes 
that  soluble  fluorine-compounds  diffuse  themselves  through 
the  rising  sap  of  the  plant,  and  are  converted,  by  the  silica 
therein  contained,  into  insoluble  silico-fluorides.  Traces  of 
fluorine  also  occur  in  the  trap-rocks  near  Edinburgh  and  in  the 
neighbourhood  of  the  Clyde,  in  the  granites  of  Aberdeenshire, 


720  FLUORINE. 

and  in  the  soils  formed  by  the  disintegration  of  such  rocks.* 
The  same  chemist  has  likewise  found  fluorine  in  the  ashes  of 
ox-blood,  milk,  cream-cheese,  and  very  slight  traces  in  the 
ash  of  the  whey,  f  For  the  detection  of  small  quantities 
of  fluorine  in  rocks,  aslies,  &c..  Professor  Wilson  heats  the 
substance  (mixed  with  silica  if  that  body  be  not  already 
present)  with  strong  sulphuric  acid  in  a  glass  vessel ;  passes 
the  evolved  fluoride  of  silicon  into  water ;  supersaturates  the 
hydrofluosilicic  acid  thus  formed  with  ammonia ;  evaporates 
to  dryness;  exhausts  the  residue  with  water;  again  evaporates 
the  filtrate;  and  tests  the  residue  in  the  ordinary  way  by 
treating  it  with  sulphuric  acid  in  a  platinum  vessel  covered 
with  a  waxed  glass  plate.  J 

Isolation  of  Fluorine. — Fremy,  by  submitting  fused  fluoride 
of  potassium  to  the  action  of  the  voltaic  battery,  has  eliminated 
a  gas  which  rapidly  attacks  platinum,  decomposes  water  with 
formation  of  hydrofluoric  acid,  and  displaces  iodine  from 
its  combinations  with  metals.  By  decomposing  fluoride  of 
calcium  at  a  red  heat  with  dry  chlorine  or  oxygen,  he  like- 
w'lSQ  obtains  a  gas  which  rapidly  attacks  glass.  This  gas 
appears  to  be  fluorine. § 

Anhydrous  hydrofluoric  acid  may  be  obtained  by  heating 
the  fluoride  of  potassium  and  hydrogen  in  a  platinum  vessel, 
or  by  decomposing  fluoride  of  lead  on  a  layer  of  charcoal  in  a 
platinum  tube  by  dry  hydrogen  gas.  It  is  gaseous  at  ordinary 
temperatures ;  but  at  the  temperature  of  a  mixture  of  ice  and 
salt,  it  condenses  into  a  very  mobile  liquid,  which  acts  vio- 
lently on  water,  forms  white  fumes  in  the  air,  and  attacks 
glass.     (Fremy.  ||) 

Estimation  of  Fluorine, — The  solid  compounds  of  fluorine 
are  decomposed  by  heating  them  in  a  platinum  crucible  with 
strong  sulphuric   acid,  the  heat  being  continued  till  all  the 

*  Edinb.  Phil.  J.  liii.  356.  f  Chcm.  Gaz.  1850,  366. 

X  Chem.  Soc.  Qu.  J.  v.  151.  §  Compt.  rend,  xxxviii.  393  ;  xl.  966. 

il  Ibid,  xxxviii.  393. 


ESTIMATION   OF   FLUORINE.  721 

fluorine  is  expelled  in  the  forni  of  hydrofluoric  acid,  and  the 
excess  of  sulphuric  acid  is  likewise  drawn  off".  The  residual 
sulphate  is  then  weighed,  and  the  quantity  of  metal  in  it  cal- 
culated ;  this  quantity  deducted  from  the  original  weight  of  the 
fluorine  gives  the  quantity  of  fluorine.  Or,  supposing  no  other 
volatile  acid  to  be  present,  if  the  difference  in  the  weight  of  the 
fluoride  and  the  sulphate  formed  from  it  be  dy  the  quantity  of 
fluorine  may  be  found  by  means  of  the  equations, 

SO.         48 


SO, -F  =  J; 


F  187 


The  second  mode  of  calculation  is  equally  applicable,  whether 
the  fluorine  be  combined  with  one  metal  or  with  several. 

Fluorides  frequently  occur  in  nature  in  conjunction  with 
phosphates,  as  in  apatite  and  in  bones.  To  analyse  such  a 
compound,  it  is  first  heated  with  sulphuric  acid  to  expel  the 
fluorine;  the  residue  digested  with  alcohol  to  dissolve  the 
phosphoric  acid  which  has  been  set  free;  the  quantity  of 
that  acid  determined  by  precipitation  with  ammonia  and  sul- 
phate of  magnesia ;  and  the  metals  now  remaining  in  the  form 
of  sulphates  determined  by  methods  already  given.  Lastly, 
the  total  weight  of  these  metals,  together  with  that  of  the 
phosphoric  acid,  or  rather  of  the  corresponding  salt-radical 
(POg,  if  the  phosphates  are  tribasic),  is  deducted  from  the 
original  weight  of  the  mineral ;  and  the  difference  gives  the 
quantity  of  fluorine. 

From  solutions,  fluorine  is  generally  precipitated  as  fluoride 
of  calcium,  from  the  weight  of  which,  if  pure,  the  quantity  of 
fluorine  may  be  immediately  calculated  ;  but  if  other  sub- 
stances are  precipitated  at  the  same  time,  the  quantity  of 
fluorine  must  be  determined  in  the  manner  above  described. 


M 


722        bunsen's  general  method 


bunsen's  general  method  of  volumetric  analysis. 

This  method,  which  is  applicable  to  a  great  number  of 
analyses  depending  upon  oxidation  and  reduction,  is  founded 
on  the  principle  of  liberating  a  quantity  of  iodine  equivalent 
to  the  substance  which  is  to  be  estimated,  and  determining 
the  amount  of  this  iodine  by  means  of  a  standard  solution  of 
sulphurous  acid. 

Iodine  and  sulphurous  acid,  in  presence  of  water,  form 
hydriodic  and  sulphuric  acids ; 

SO2  +  I  +  HO  =  SO3  +  HI, 

each  equivalent  of  sulphurous  acid  thus  transformed  corre- 
sponding to  1  eq.  of  iodine,  or  32  parts  by  weight  of  anhy- 
drous sulphurous  acid  to  126*36  parts  of  iodine. 

For  this  reaction,  however,  it  is  necessary  that  the  liquids 
be  very  dilute ;  for,  at  a  certain  degree  of  concentration,  the 
opposite  change  takes  place,  sulphuric  and  hydriodic  acids 
decomposing  each  other  in  such  a  manner  as  to  yield  sulphu- 
rous acid,  water,  and  iodine.  The  solution  of  sulphurous 
acid  used  for  the  estimation  of  iodine  must  never  contain  more 
than  from  0*04  to  0*05  per  cent,  of  iodine. 

The  method  requires  three  standard  test-liquids :  a  solution 
of  iodine,  a  solution  of  sulphurous  acid,  and  a  solution  of 
iodide  of  potassium.  To  prepare  the  first,  a  weighed  quantity 
of  iodine,  as  pure  as  can  be  obtained,  is  dissolved  in  a  con- 
centrated solution  of  iodide  of  potassium  (which  must  be  per- 
fectly free  from  free  iodine  and  iodate  of  potash,  and  there- 
fore must  not  exhibit  any  brown  colour,  either  by  itself  or  on 
addition  of  hydrochloric  acid),  and  the  liquid  diluted  to  such 
a  degree  that  200  cubic  centimeters  may  contain  1  gramme  of 
iodine,  so  that,  if  a  division  of  the  burette  contains  half  a 
cubic  centimeter,  each  degree  may  contain  -^-^  or  0-0025  of  a 
gramme  of  the  iodine  used.  But  as  commercial  iodine,  even 
the  purest,  contains  traces  of  chlorine,  it  is  necessary  to  de- 


OF   VOLUMETRIC   ANALYSIS.  723 

termine  the  real  value  in  iodine  of  a  degree  of  the  burette  by 
special  experiment.  The  method  of  doing  this  will  be  pre- 
sently described  (p.  727). 

Of  tlie  second  test-liquid,  the  dilute  sulphurous  acid,  it  is 
best  to  prepare  a  considerable  quantity,  20  or  30  litres,  at  a 
time,  so  that  the  alteration  produced  in  it  by  the  oxidising 
action  of  the  air  during  the  course  of  an  experiment,  or  even 
in  a  day,  may  be  imperceptibly  small.  To  give  the  acid  the 
proper  degree  of  solution,  20  or  30  litres  of  water  are  mixed 
with  a  small  measure-glassful  of  concentrated  sulphurous 
acid ;  the  liquid  shaken ;  200  burette-degrees,  or  100  cubic 
centlm.  of  it  measured  off;  this  portion  of  liquid  mixed  with 
starch,  and  the  standard  solution  of  iodine  added  from  the 
burette,  till  the  liquid  just  exhibits  a  perceptible  blue  colour. 
If  the  number  of  burette-degrees  of  the  iodine-solution  re- 
quired for  this  purpose  be  t,  and  the  quantity  of  iodine  in  one 
degree  be  a,  the  quantity,  x,  of  anhydrous  sulphurous  acid,  S, 
in  100  degrees  of  the  acid  solution  will  be 

S  32 

£0   =   — .  at   =    .  at, 

I  126-36  ^ 

The  most  convenient  strength  of  the  sulphurous  acid  solution 
is  about  0*03  anhydrous  sulphurous  acid  to  100  water.*  It 
must  be  tested  at  the  commencement  of  each  day's  work,  and 
will  require  renewal  after  three  or  four  days.f 

The  third  test-liquid  is  a  solution  of  pure  iodide  of  po- 
tassium, containing  about  1  grm.  of  tke  iodide  to  10  cubic 
centimetres  of  water. 

1 .  Determination  of  the  amount  of  pure  Iodine  in  a  commercial 
sample. — The  w^eighed  sample  is  dissolved  in  the  solution  of 
iodide  of  potassium,  in  the  proportion  of  about  0-1  grm.  to 

*  As  a  cubic  centimeter  of  water  weighs  a  gramme,  this  is  the  same  as 
0*03  grm.  in  100  cubic  centimeters  or  200  burette-divisions. 

f  A  modification  of  this  method,  in  which  hyposulphite  of  soda  is  used  in- 
stead of  sulphurous  acid,  has  been  introduced  by  Mr.  E.  0.  Brown.  (See  page 
1 09  of  this  volume.) 


724        bunsen's  general  method 

4  or  5  cub.  centim.  of  liquid.  To  the  resulting  brown  solution, 
as  many  measures,  n,  of  the  standard-solution  of  sulphurous 
acid  are  added,  as  are  required  to  destroy  the  brown  colour 
completely.  The  next  step  is  to  determine  the  quantity  of 
iodine,  x,  by  which  this  quantity  of  sulphurous  acid  has  been 
partially  decomposed.  This  is  effected  by  adding  three  or 
four  cubic  centimeters  of  clear  and  very  dilute  starch- solution, 
and  then  dropping  in  the  standard-solution  of  iodine  from  the 
burette,  till  a  blue  colour  begins  to  appear.  If  t'  degrees  of 
the  iodine-solution  are  required  for  this  purpose,  and  the 
quantity  of  iodine  in  each  degree  is  a,  the  quantity  required 
to  decompose  completely  the  n  measures  of  sulphurous  acid 
is  ^  -f  at\  Further,  if  we  determine  the  quantity  of  iodine, 
a  t,  required  to  decompose  one  measure  of  the  sulphurous  acid 
solution,  we  shall  obtain  the  equation  x  +  at'  =  nat ;  whence 

00  =  a  (nt  —  f). 

If  the  weight  of  the  sample  of  iodine  be  A,  the  quantity  ex- 

.„  ,     100«    ^  ,^         ,  .^  100  a 

pressed  as  a  percentage  will  be  —z —   (nt  —  f) ;  and  it  — ^ — 

=  1,  that  is,  if  the  quantity  weighed  out  is  exactly  100  a 
(4  grms.  if  a  =  -^^  grm.),  the  difference  of  the  two 
measurements,  nt—if,  gives  at  once  the  per  centage  of  iodine 
in  the  sample. 

The  same  method  may  be  applied  to  determine  the  quan- 
tity of  free  iodine  contained  in  any  liquid. 

2.  Determination  of  Chlorine. — Chlorine  decomposes  a  solu- 
tion of  iodide  of  potassium  instantly  and  completely,  without  the 
aid  of  heat,  setting  free  an  equivalent  quantity  of  iodine.  If 
this  quantity  of  liberated  iodine  be  determined  in  the  manner 
just  described,  the  quantity  of  chlorine  will  be  given  by  the 
equation, 

CI      . 

X   =:   -r-  a  {nt  —  v). 

3.  Similarly  for  Bromine : 

a;   =       y-  .  a  {nt  —  t). 


OF   VOLUMETRIC   ANALYSIS.'  125 

4.  Chlorine  and  Bromine  together, — To  estimate  the  quan- 
tity of  chlorine  contained  in  a  sample  of  bromine,  a  quantity 
A  of  the  bromine,  thoroughly  dried,  is  dissolved  in  a  solution 
of  iodide  of  potassium,  and  the  quantity  of  iodine,  a  (nt  —  f) 
thereby  separated,  is  determined  as  above.  Then,  denoting 
the  quantity  of  bromine  by  x,  and  that  of  chlorine  by  ?/,  we 
have  the  equations :  — 

X  +  y  -  A; 


gj^  +   Q^y  -  a{nt  -^  0; 

-1-  J.  —  a{nt  —  t')            a  {nt  - 
Cl              Br                        01 

I              • 

Br 

whence     x  = 


If  the  chlorine  and  bromine  are  in  a  state  of  combination, 
they  may  be  set  free  by  distilling  the  mixture  or  compound 
with  bichromate  of  potash  and  sulphuric  acid,  the  evolved 
gases  being  passed  into  the  solution  of  iodide  of  potassium. 

A  similar  method  may  be  applied  to  a  mixture  of  chlorine 
and  iodine,  the  equations  then  becoming — 

X  +  y  =  A;     T^  X  -{-  y  ^  a  (nt  —  t'). 

5.  Chlorites  and  Hypochlorites. — A  solution  of  the  salt  is 
mixed  with  solution  of  iodide  of  potassium,  and  hydrochloric 
acid  added  in  slight  excess.  From  the  quantity  of  iodine, 
a  (nt—tf)  thus  separated,  the  quantity  of  chlorous  acid  x\  or 
hypochlorous  acid  x^^j  may  be  determined  from  the  equations 

ci 

x^  =  -Tj  a  (nt  —  f) 

Cl 

^"  =  ^  a  (nt  —  «') 

It  must  be  remembered  that  1  eq.  CIO  decomposes  2  eq.  KI, 
and  1  eq.  CIO3  decomposes  4KI. 
VOL.  II.  3  D 


726        bunsen's  general  method 

This  method  is  well  adapted  to  the  estimation  of  chloride  of 
lime  for  commercial  purposes.     If  A  be  the  weight  of  the 

sample,  the  percentage  of  chlorine  will  be  —^ — p-  a  (nt  —  f)  ; 

and  if  A  be  equal  to j —   a,   the   difference   of  the  two 

measurements,  nt  —  f,  gives  directly  the  bleaching  power  of 
the  product  in  percentage  of  chlorine. 

6.  Chromates,  —  When  a  chromate,  e,  g.  bichromate  of 
potash,  is  boiled  with  excess  of  fuming  hydrochloric  acid, 
every  2  eq.  chromic  acid  eliminate  3  eq.  chlorine : — 

2Cr03  +  6HC1  =  Cr^Clg  +  6H0  +  3C1 ; 

and  the  3  eq.  of  chlorine  passed  into  a  solution  of  iodide  of 
potassium,  liberate  3  eq.  of  iodine,  which  may  be  estimated 
volumetrically  as  above.  Hence  the  quantity  x  of  chromic 
acid  contained  in  a  known  weight  A  of  bichromate  of  potash, 
or  any  other  chromate,  will  be  given  by  the  equation — 

2  Cr     , 

.     .r.  200  Cr      - 

or  m  100  parts :   x  =  -^ — itj—  a  {nt  ^  t ). 

200  Cr 

If -4  = — ^"Y —  a,  that  is,  if  the  sample  taken  weighs  exactly 

this  quantity,  the  difference  of  the  two  measurements,  nt  —  ^, 
gives  directly  the  percentage  of  chromic  acid.     Similarly,  for 

A  =  100 — oT a,  this  difference  would  give  the  percentage 

Pb  -I-    Pr 
of  pure  bichromate  of  potash,  and  for  A  =  200  ^j a, 

tlie  percentage  of  pure  chromate  of  lead  in  these  respective 
salts. 


OF   VOLUMETRIC   ANALYSIS.  727 

The  analysis  is  made  by  introducing  a  weighed  quantity  of 
the  chromate  into  a  small  flask  holding  about  40  cubic  centi- 
meters, filled  about  two-thirds  with  fuming  hydrochloric  acid, 
and  having  a  gas-delivery  tube  adapted  to  its  neck  by  means 
of  a  tube  of  vulcanised  caoutchouc.  The  glass  tube  is  in- 
serted into  the  neck  of  an  inverted  retort,  of  the  capacity  of 
about  160  cubic  centim.,  containing  a  solution  of  iodide  of 
potassium.  The  middle  of  the  neck  of  the  retort  is  blown 
out  into  a  bulb  to  receive  any  liquid  that  may  be  thrown  up. 
A  piece  of  vulcanised  caoutchouc  is  tied  tightly  over  the  open 
end  of  the  glass  tube,  and  a  slit  cut  in  it  with  a  sharp,  wet 
penknife.  This  slit  opens  when  pressed  from  within,  but 
closes  tightly  when  pressed  in  the  opposite  direction,  thus 
forming  an  excellent  valve.  Tiie  liquid  in  the  flask  is  now 
boiled  for  three  or  four  minutes,  by  which  time  the  whole  of 
the  chlorine  is  expelled,  and  an  equivalent  quantity  of  iodine 
liberated. 

The  volumetric  analysis  of  pure  bichromate  of  potash 
affords  an  easy  method  of  determining  the  value  of  a,  or  the 
quantity  of  pure  iodine  contained  in  a  burette  degree  of  the 
standard  solution  (p.  723).     For  if  the  bichromate  of  potash 

K  +  2  Cr 

be  pure,  its  weight  A  is  exactly  equal  to q-j a  (jit  —  f) ; 

therefore, 


a 


(k  +  2  Cr)  {nt  -  f) 


7.  Peroxides. — The  quantity  of  oxygen  in  the  peroxides  of 
lead,  manganese,  &c.,  may  be  estimated  in  a  similar  manner 
to  chromic  acid.  Thus,  the  percentage  of  oxygen  in  binoxide 
of  lead  PbOg  is  given  by  the  formula  — 

20 

X  =  100  J— J  a  {nt  —  t'); 

3  D  2 


728    bunsen's  method  of  volumetric  analysis. 

and  the  percentage  of  pure  binoxide  of  manganese  in  a  com- 
mercial sample  of  the  black  oxide  by  the  formula  — 

100  Mn      , 

w  =    —2 — r —  a  {lit  —  t'). 

Besides  the  preceding  and  a  great  number  of  other  bodies 
which  give  rise  to  a  separation  of  free  chlorine,  the  iodome- 
tric  method  may  be  applied  to  the  estimation  of  substances 
which  are  raised  by  chlorine  to  a  higher  degree  of  oxidation. 
These  substances  are  heated  with  fuming  hydrochloric  acid 
and  a  known  weight,  p,  of  pure  bichromate  of  potash ;  the 
evolved  chlorine  is  passed  into  iodide  of  potassium ;  and  the 
liberated  iodine  estimated  as  above.  The  quantity  thus  sepa- 
rated, viz.  a  (nt   •—   t'),  is  equal  to  the  quantity  of  iodine, 

77  ,  equivalent  to  the  bichromate  used  minus  the  quan- 


K  +  2Cr 

tity  iy  equivalent  to  the  protoxide  to  be  estimated.    The  latter 

is  therefore, 

p.  31 

K  +  2Cr 

Thus,  to  determine  the  amount  of  protoxide  of  iron  in  a 
given  sample  of  iron-ore,  it  must  be  remembered  that  each 
equivalent  of  iodine  or  chlorine  converts  2  eq.  of  the  protoxide 
into  sesquioxide : — 

2FeO  +  I  +  HO  =  Fe^Og  +  HI. 

If  then  i  be  the  quantity  of  iodine  required  to  convert  the 
protoxide  of   iron  in   a  given  sample  into  sesquioxide,  the 

quantity  e  of  protoxide  in  this  sample  will  be  e  =  i  .  — — ; 
and  substituting  for  i  its  value  above  given,  we  have 

6  Fe  2  F'e       ,  ,       ,„ 

e  = p  —  — - —  a  (lit  —  t) ; 

K  -f  2C)r  ^ 


PREPARATION   OF   POTASSIUM.  729* 

and  hence  it  is  easy  to  calculate  the  equivalent  quantities  of 
metallic  iron  and  sesquioxide. 

Various  other  applications  of  the  method,  will  be  found  in 
Professor  Bunsen's  memoir.* 


METALS  OF  THE  ALKALIES  AND  EARTHS. 

POTASSIUM. 

Preparation  of  Potassium, — The  process  of  obtaining  this 
metal  by  igniting  a  mixture  of  carbonate  of  potash  and 
charcoal,  has  received  considerable  improvements  from  the 
researches  of  Maresca  and  Donny.f  The  ordinary  form 
of  the  process,  which  is  that  devised  by  Brunner,  is 
dangerous,  and  gives  very  uncertain  results,  the  quantity 
of  metal  obtained  by  it  being  often  very  small,  and  some- 
times, even  when  the  greatest  care  is  taken,  absolutely 
nothing.  The  danger  arises  from  the  obstruction  of  the 
connecting  tube  by  the  black  substance  formed  by  the 
action  of  carbonic  oxide  on  the  potassium  there  deposited ; 
and  the  loss  of  product  is  due,  partly  to  the  formation  of 
this  black  substance,  and  partly  to  the  escape  of  portions 
of  the  metal  in  the  form  of  vapour.  The  first  of  these 
inconveniences  can  only  be  obviated  by  keeping  the  entire 
length  of  the  connecting  tube  at  a  red  heat  during  the 
whole  operation.  But  in  that  case,  if  the  large  receivers 
invented  by  Brunner  (see  figures  152,  153,  p.  521,  Vol.  L) 
are  used,  not  a  particle  of  the  metal  condenses,  the  whole 
escaping  in  the  form  of  vapour.  Hence  it  is  necessary  to 
use  much  smaller  receivers ;  and  the  form  which  the  authors 

*  Ann.  Ch.  Pharm.  Ixxxvi.  265  ;  Chcm.  Soc.  Qu.  J.  viii.  218. 
t  Ann.  Ch.  Pliys.  [3],  xxxv.  147. 
3d  3 


730  POTASSIUM. 

find  to  give  the  best  results,  is  that  of  a  shallow  rectangular 
box,  12  centimeters  long,  6  wide  and  4  deep.  Another 
source  of  failure  in  the  operation  is  the  want  of  a  due  pro- 
portion between  the  carbonate  of  potash  and  charcoal  in  the 
calcined  tartar.  To  obtain  the  best  result,  the  quantity  of 
charcoal  should  be  neither  more  nor  less  than  that  which  is 
theoretically  required  for  the  complete  reduction  of  the  potash 
present.  Whether  this  is  the  case,  can  only  be  ascertained 
by  a  previous  analysis  of  the  burnt  tartar ;  and  any  excess 
or  deficiency  of  charcoal,  must  be  remedied  by  mixing 
samples  of  tartar  of  different  qualities.  Lastly,  to  prevent 
the  perforation  of  the  iron  bottle  daring  the  ignition,  it  should 
be  coated,  not  with  clay  luting,  but  with  fused  barax.  Such  a 
coating  is  easily  formed  by  sprinkling  pulverised  borax  on  the 
bottle  when  it  is  at  a  dull  red  heat. 

Preparation  of  Potassium  hy  Electrolysis,  —  A  mixture  of 
1  at.  chloride  of  potassium  and  1  at.  chloride  of  calcium 
(which  mixture  is  used  because  it  melts  at  a  much  lower 
temperature  than  chloride  of  potassium  alone),  is  melted  in  a 
small  porcelain  crucible  over  a  lamp,  and  subjected  to  the 
action  of  a  Bunsen's  battery  of  six  elements  with  carbon  poles, 
the  heat  being  so  regulated  that  a  solid  crust  forms  round  the 
negative  carbon  pole,  while  the  mixture  remains  fused  and 
allows  the  free  evolution  of  chlorine  at  the  positive  pole. 
When  the  decomposition  has  been  continued  in  this  manner 
for  about  twenty  minutes,  and  the  cooled  crucible  is  opened 
under  rock-oil,  a  large  quantity  of  potassium,  almost  chemi- 
cally pure,  is  generally  obtained.  If  the  same  experiment  be 
repeated  at  a  white  heat  over  a  charcoal  fire,  with  an  iron 
wire  as  negative  pole,  small  globules  of  potassium  are  seen 
burning  on  the  surface ;  and  these  when  analysed,  are  found 
to  be  almost  pure.     (Matthiessen.*) 

Preparation  of  pure  Hydrate  of  Potash. —  Wohler  recom- 
mends for  this  purpose   the  decomposition  of  pure  nitre  by 

*  Chcm.  Soc.  Qii.  J.  viii.  30. 


ESTIMATION   OF   POTASSIUM.  73l 

metallic  copper  at  a  red  heat.  1  pt.  of  nitre  and  2  or  3  pts. 
of  thin  copper  plate  cut  into  small  pieces,  are  arranged  in 
alternate  thin  layers  in  a  covered  copper  crucible,  and  exposed 
for  half  an  hour  to  a  moderate  red  heat.  The  cooled  mass 
is  then  treated  with  water,  the  liquid  left  to  stand  in  a  tall 
covered  cylindrical  vessel  till  the  oxide  of  copper  has  com- 
pletely settled  down,  and  the  pure  solution  of  potash  then 
decanted  with  a  siphon. 

With  the  above  proportions  of  nitre  and  copper  part  of  the 
latter  is  converted  only  into  suboxide.  It  may,  therefore,  be 
used  for  a  second  preparation  of  potash,  by  mixing  1  pt.  of  it 
with  1  pt.  of  nitre  and  1  pt.  of  metallic  copper. 

Iron  may  also  be  used  to  decompose  the  nitre ;  but  the 
potash  thereby  obtained  is  contaminated  with  small  quantities 
of  carbonic  acid,  silica,  &c.  The  same  objection  applies  to 
the  use  of  an  iron  crucible,  if  a  perfectly  pure  product  be  re- 
quired.* 

Estimation  of  Potassium,  —  Potassium,  when  it  occurs  in  a 
compound  not  containing  any  other  metal,  may  be  estimated 
either  as  sulphate  or  as  chloride.  All  potassium-salts  con- 
taining volatile  acids,  are  decomposed  by  heating  them  with 
sulphuric  acid,  the  excess  of  which  may  afterwards  be 
expelled  by  a  stronger  heat,  and  the  quantity  of  potassium  or 
potash  calculated  from  the  weight  of  the  residual  neutral  sul- 
phate. It  is  difficult,  however,  to  expel  the  last  traces  of  free 
sulphuric  acid  by  mere  ignition ;  but  they  may  be  completely 
driven  off  by  dropping  a  lump  of  carbonate  of  ammonia 
into  the  crucible,  and  repeating  the  ignition  with  the  cover 
on ;  the  sulphuric  acid  then  diffuses  into  the  atmosphere 
of  ammonia  in  the  crucible,  and  a  perfectly  neutral  sulphate 
remains.     It  contains  54*06  per  cent,  of  potash,  KO. 

In  estimating  potassium  as  chloride,  the  only  precaution 
to  be  observed  is  to  ignite  the  chloride  in  a  covered  crucible, 

*  Ann.  Ch.  Pharm.  Ixxxvii.  373. 
3  D  4 


732  SODIUM, 

as,  when  strongly  heated  in  contact  with  the  air,  a  portion  of 
it  volatilises.  The  chloride  contains  52-47  per  cent,  of 
potassium,  equivalent  to  63*19  per  cent,  of  potash. 

The  separation  of  potassium  from  all  soluble  substances 
except  ammonia,  is  easily  effected  by  precipitating  it  with 
bichloride  of  platinum,  adding  alcohol  to  complete  the  preci- 
pitation of  the  chloroplatinate  of  potassium,  collecting  the 
precipitate  on  a  weighed  filter,  washing  with  alcohol,  and 
drying  it  at  100°  C.  It  contains  16-04  per  cent,  of  potassium 
equivalent  to  19*31  of  potash. 

SODIUM. 

Preparation. — Deville  finds  that  the  reduction  of  this  metal 
from  the  carbonate,  by  ignition  with  charcoal,  is  greatly 
facilitated  by  the  addition  of  some  substance,  such  as  chalk, 
which  retains  the  mass  in  a  pasty  state  during  ignition.  The 
best  product  is  obtained  with  a  mixture  of  7 1 7  pts.  of  dry 
carbonate  of  soda,  175  charcoal,  and  108  chalk.  With 
regard  to  the  form  of  apparatus,  and  the  mode  of  conducting 
the  process,  Deville  follows  exactly  the  directions  given  by 
Maresca  and  Donny  (p.  729),  for  the  preparation  of  potas- 
sium.* 

Sodium  may  be  readily  obtained  by  electrolysis,  in  a  man- 
ner similar  to  that  described  for  potassium  (p.  730),  using, 
however,  a  mixture  of  1  at.  chloride  of  sodium,  and  2  at. 
chloride  of  calcium.     (Matthiessen.) 

Carbonate  of  Soda. — Solutions  of  carbonate  of  soda  are 
capable  of  assuming  the  state  of  supersaturation,  and  exhi- 
biting phenomena  similar  to  those  of  the  sulphate  (I.  555). 
An  aqueous  solution  of  the  salt,  saturated  at  a  high  tempera- 
ture, and  enclosed  while  boiling  hot  in  sealed  tubes  or  well- 
corked  flasks,  remains  supersaturated  at  ordinary  temperatures, 

*  Ann.  Ch.  Phys.  [3],  xliii.  5. 


CARBONATE   OF   SODA.  733 

and  frequently,  even  when  cooled  several  degrees  below  0°  C, 
not  depositing  any  crystals.  Keeping  the  air  in  contact  with 
the  liquid  from  agitation  (as  by  covering  the  hot  solution 
with  a  glass  receiver),  is  often  sufficient  to  prevent  the 
formation  of  crystals  at  ordinary  temperatures ;  but  free 
access  of  air  causes  immediate  solidification,  attended  with 
rise  of  temperature.  The  passage  of  an  electric  current 
through  a  supersaturated  solution,  does  not  induce  any  change 
of  state. 

The  supersaturated  solutions  of  carbonate  of  soda  contain 
a  salt  having  less  water  of  crystallisation  than  the  ordinary 
10-hydrated  salt.  The  salt  contained  in  them  is,  in  fact,  a 
7-hydrated  salt,  NaO .  COg  4-  7H0,  and  of  this  salt  there  are 
two  modifications,  differing  in  crystalline  form  and  in  degree 
of  solubility.  One  of  them  (a)  crystallises  in  rhombohedral 
crystals  ;  the  other  (h),  in  square  tables  or  low  prisms :  both 
these  salts  absorb  water  rapidly*  The  salt  h  was  first  ob- 
tained by  Thomson,  who,  however,  supposed  it  to  contain 
8  at.  water.  When  a  solution  saturated  at  the  boiling  heat,  and 
containing  a  slight  excess  of  the  solid  salt,  is  enclosed  in  a 
flask,  which  is  corked  immediately  after  the  boiling  has  ceased, 
no  crystals  are  deposited  from  it  for  a  long  time  on  cooling  down 
to  between  25°  and  18°  C.  ;  but  on  cooling  below  8°,  it  deposits 
chiefly  the  salt  b.  When  cooled  to  between  16°  and  10°,  it  yields 
the  salt  a,  which  redissolves  between  21°  and  22°,  forms  again 
on  cooling  to  1 9° ;  and  on  cooling  from  10°  to  4°,  becomes  opaque, 
and  passes  into  the  salt  b.  After  cooling  to  a  lower  tempera- 
ture, and  for  a  longer  time,  when  the  state  of  supersaturation 
ceases,  the  whole  is  converted  into  a  mass  of  crystals  of  the 
ordinary  salt  NaO  .  COg  +  10  aq.  The  following  table 
gives  a  comparative  view  of  the  quantities  of  the  10-hydrated 
and  of  the  two  varieties  of  the  7-hydrated  salt,  contained 
in  100  parts  of  the  saturated  solutions  at  different  tempera- 
tures : — 


;4 

SODIUM. 

Temperature     , 

.      0° 

10°      15°      20° 

25° 

30° 

38° 

104°. 

10-hydrated  salt 

.     70 

12-1     16-2     21-7 

28-5 

37  2 

51-7 

45-5 

7-hyclrated  (b)  . 

.  20-4 

26-3     29-6     38-6 

38-1 

43-5 

— 

— 

7-hydrated  (a)  . 

.  31-9 

37-9     41-6     45-8 

— 

— 

— 

— 

Hence  it  appears,  that  carbonate  of  soda  exhibits  a  maxi- 
mum of  solubility,  at  38°  C.  The  decrease  of  solubility  above 
this  point  arises  from  the  formation  of  another  hydrate, 
NaO  .  COg  +  HO.  This  hydrate,  which  separates  out 
when  a  solution  saturated  at  104°  C.  is  concentrated  by 
boiling,  is  more  soluble  in  cold  than  in  hot  water,  and  the 
crystals  which  have  been  separated  by  boiling,  redissolve  in 
the  mother  liquor,  when  left  to  cool  in  a  closed  vessel. 
(H.  Loewel.*) 

Besides  the  hydrates  above-mentioned,  two  others  have 
been  discovered  by  Jacquelainf,  viz.  NaO.COg  +  15H0, 
which  crystallises  below  —  20°,  and  when  dried  in  vacuo 
gives  off  5  atoms  of  water,  and  is  converted  into  the  ordinary 
ten-hydrated  salt ;  and  NaO  .  COg  +  9H0,  obtained  by  re- 
peatedly crystallising  a  solution  which  at  first  contains  a 
portion  of  bicarbonate  of  soda.  Jacquelain  also  finds  that 
carbonate  of  soda  gives  off  carbonic  acid  when  melted,  even 
in  a  stream  of  pure  and  dry  carbonic  acid. 

Sulphate  of  Soda. — This  salt  appears  to  be  capable  of 
existing  in  solution  in  three  different  states,  viz.  as  anhy- 
drous salt,  NaO.  SO3,  as  the  seven-hydrated  salt,  NaO.  SO3 
+  7H0,  and  as  the  ten-hydrated  salt,  NaO.S03+  lOHO, 
which  is  the  ordinary  Glauber's  salt.  The  following  table 
shows  the  solubility  (as  determined  by  Loewel  J)  of  the  anhy- 
drous salt,  and  of  the  two  hydrates,  in  water,  at  various 
temperatures ;  also  the  quantity  of  anhydrous  salt  corre- 
sponding in  each  case  to  the  hydrate  dissolved.  The  numbers 
in  the  table  are  the  quantities  of  salt  dissolved  in  100  parts 
of  water. 

*  Ann.  Ch,  Phys.  [3],  xxxiii.  334. 

f  Compt.  rend.  xxx.  106. 

X  Ann.  Ch.  Phys.  [3],  xlix.  32. 


ESTIMATION  OF   SODIUM. 

Solubility  op  Sulphate  op  Soda. 


735 


NaO .  SO3, 

NaO. SO 

3  +  lOHO. 

NaO. SO 

3  +  7HO. 

Temp. 

Anhydrous. 

Anhydrous. 

Hydrate. 

Anhydrous. 

Hydrate. 

QOC. 

5-02 

12-16 

19-62 

44-84 

10 

, 

9-00 

2304 

30-49 

78-90 

15 

,             , 

13-20 

35-96 

37-43 

105-79 

18 

52-25 

16-80 

4841 

41-63 

124-59 

20 

52-76 

19-40 

58-35 

44-73 

140-01 

25 

51-53 

28-00 

98-48 

52-94 

188-46 

26 

51-31 

30-00 

109-81 

54-07 

202-61 

30 

50-37 

40-00 

184-09 

33 

49-71 

50-76 

323-13 

34 

49-53 

55-00 

412-22 

40-15 

48-78 

50-40 

46-82 

59-79 

45--12 

70-61 

44-35 

84-42 

42-96 

103-17 

4265 

Sulphate  of  Soda  and  Potash,  —  Gladstone*  has  obtained  a 

salt  containing       -^r  q  [  6SO3,  by  fusing  the  neutral  or  acid 

sulphate  of  potash  with  chloride  of  sodium,  or  sulphate  of 
potash  with  sulphate  of  soda,  dissolving  the  fused  mass  in  hot 
water,  and  leaving  it  to  crystallise,  or  by  mixing  the  two  salts 
in  hot  aqueous  solution.  The  salt  which  crystallised  out 
vv^as  anhydrous,  and  exhibited  the  crystalline  form  of  sulphate 
of  potash.  H.  Rosef  had  previously  obtained  the  same  salt, 
but  had  not  assured  himself  of  its  definite  constitution. 

Estimation  of  Sodium, — This  metal,  like  potassium,  may  be 
estimated  either  as  chloride  or  as  sulphate.  The  sulphate 
contains  32*54,  and  the  chloride  39*53  per  cent,  of  sodium. 

Sodium  is  separated  from  potassium  by  means  of  bichloride 
of  platinum,  with  addition  of  alcohol,  which  precipitates  the 
potassium,  and  leaves  the  sodium  in  solution.  The  quantity 
of  potassium  may  then  be  determined  from  the  weight  of  the 

*  Chem.  Soc.  Qu.  J.  vi.  106. 
\  Fogg.  Ann.  lii.  452. 


736  AMMONIUM. 

precipitate,  and  the  sodium  estimated  by  difference.  Or  if  a 
direct  estimation  of  the  sodium  be  desired,  the  filtered  liquid 
may  be  freed  from  excess  of  platinum  by  means  of  hydrosul- 
phuric  acid,  and  the  sodium  in  the  filtrate,  which  then  con- 
tains no  other  metal,  determined  as  sulphate. 

If  the  potassium  and  sodium  are  in  the  form  of  chlorides, 
the  method  just  described  may  be  applied  immediately ;  if 
not,  it  is  best  first  to  convert  them  into  chlorides,  which  may 
in  some  cases  be  done  by  merely  heating  the  mixed  salts  with 
excess  of  hydrochloric  acid,  or,  in  case  of  sulphuric  or  phos- 
phoric acid  being  present,  by  precipitating  the  acid  with 
chloride  of  barium,  removing  the  excess  of  barium  with  car- 
bonate of  ammonia,  and  expelling  the  ammoniacal  salts  from 
the  filtrate  by  evaporation  and  ignition.  The  residue  is  a 
mixture  of  the  chlorides  of  potassium  and  sodium. 


AMMONIUM. 

A  compound  radical  consisting  of  ammonia  with  an  addi- 
tional atom  of  hydrogen,  was  first  supposed  to  exist  in  the 
ordinary  salts  of  ammonia  by  Berzelius,  and  termed  ammo- 
nium. This  body  has  never  been  insulated,  but  is  supposed 
to  appear,  in  a  certain  experiment,  in  combination  with 
mercury,  and  possessed  of  the  metallic  character  (I.  203). 
The  compounds  of  ammonium  are  always  strictly  isomor- 
phous  with  the  corresponding  compounds  of  potassium. 

Chloride  of  ammonium,  Hydrodilorate  or  Muriate  of  ammonia, 
Sal-ammoniac,  NH^ .  CI. — This  salt  is  formed  when  ammonia 
is  neutralised  by  hydrochloric  acid  ;  NH3  +  HCl  =  NH4 .  CI. 
It  is  prepared  in  large  quantity  from  the  ammoniacal  liquor 
obtained  in  the  distillation  of  bones,  in  the  manufacture 
of  animal  charcoal,  and  from  the  liquor  which  condenses  in 
the  distillation  of  coal  for  gas.  These  liquors  contain  am- 
monia principally  in  the  state  of  carbonate  and  hydrosulphate, 
which  may  be  converted  into  chloride  of  ammonium  by  the 


SULPHIDES   OF   AMMONIUM.  737 

addition  of  hydrochloric  acid.  The  salt  is  purified  by  crys- 
tallisation, and  sublimed  in  vessels  of  iron  or  earthenware,  in 
the  upper  part  of  which  it  condenses  and  forms  a  solid  cake, 
the  condition  in  which  sal  ammoniac  is  always  met  with  in 
commerce. 

Sal-ammoniac  is  tenacious  and  difficult  to  reduce  to  powder : 
its  sp.  gr.  is  1*45.  It  has  a  sharp  and  acrid  taste,  and  dis- 
solves in  2*72  parts  of  cold,  and  in  an  equal  weight  of  boiling 
water  ;  it  is  also  soluble  in  alcohol.  It  generally  crystallises 
from  solution  in  feathery  crystals,  which  are  formed  of  rows 
of  minute  octohedrons  attached  by  their  extremities.  At  a 
red  heat  it  volatilises  without  previous  fusion. 

A  corresponding  bromide,  iodide,  and  fluoride  of  ammonium 
may  be  formed  by  neutralising  ammonia  with  hydrobromic, 
hydriodic,  and  hydrofluoric  acids. 

Sulphides  of  Ammonium. — When  4  volumes  of  ammonia 
combine  with  2  of  hydrosulphuric  acid  gas,  the  sulphide  of 
ammonium  is  produced;  NHg-f  HS  =  NH^.S.  Ammo- 
nium combines  with  sulphur  in  several  other  proportions, 
which  are  obtained  on  mixing  and  distilling  the  various  sul- 
phides of  potassium  with  sal  ammoniac.  In  the  reciprocal 
decomposition  which  occurs,  the  potassium  combines  simply 
with  chlorine,  and  the  ammonium  with  sulphur.  The  fol- 
lowing compounds  are  generally  enumerated :  NH^ .  S ;  NH^ .  S 
+  HS  ;  NH4 .  S3  and  NH^.  S^.  The  protosulphide  has  long 
been  formed  by  distilling  a  mixture  of  quicklime,  sulphur, 
and  sal  ammoniac,  and  known  under  the  name  of  the  fuming 
liquor  of  Boyle.  It  is  a  volatile  liquid,  the  vapour  of  which  is 
decomposed  by  oxygen,  and  thus  fumes  produced.  The 
second  compound,  which  is  a  sulphide  of  hydrogen  and  am- 
monium, is  formed  by  transmitting  hydrosulphuric  acid  gas 
through  solution  of  ammonia  to  saturation.  This  liquid  is  gene- 
rally called  the  hydrosulphate  of  ammonia,  and  is  a  very  useful 
reagent  in  chemical  analysis.  All  the  sulphides  of  ammo- 
nium are  soluble  in  water  and  alcohol  without  decomposition. 


V38  AlVIMONIUM. 

Nitrate  of  ammonium,  NH4O.NO5. — When  nitric  acid  is 
saturated  with  ammonia,  a  salt  is  obtained  which  crystallises 
in  six-sided  prisms,  and  is  isomorphous  with  nitrate  of  potash. 
Besides  the  elements  of  anhydrous  nitric  acid  and  ammonia, 
this  salt  contains  an  atom  of  water  which  cannot  be  separated 
from  it,  which  is  also  found  in,  and  is  equally  essential  to,  the 
salts  formed  by  neutralising  all  other  oxygen-acids  by  am- 
monia, such  as  sulphurous  acid,  sulphuric,  carbonic,  &c.,  in 
contact  with  water.  The  hydrogen  of  this  water  is  assigned 
to  the  ammonia,  to  form  ammonium,  which  the  oxygen 
converts  into  oxide  of  ammonium  ;  so  that  the  product  is 
nitrate  of  the  oxide  of  ammonium  ;  or  NH3  +  HO  .  NO5  = 
NH4O .  NO5.  This  salt  deflagrates  with  flame  when  thrown 
upon  red-hot  coals.  When  decomposed  between  300°  and 
400°,  it  is  resolved  into  water  and  nitrous  oxide  (I.  339). 

Carbonates  of  Ammonium, — The  neutral  carbonate  of  oxide 
of  ammonium  appears  not  to  exist  in  the  free  state,  but  by 
distilling  the  sesquicarbonate  of  ammonia  of  the  shops  at  a 
gentle  heat.  Rose  obtained  a  volatile  crystalline  salt,  which 
may  be  viewed  as  a  compound  of  anhydrous  carbonate 
of  ammonia  with  carbonate  of  ammonium  :  NH3 .  COg  + 
NH4O .  COg.  When  the  commercial  salt  is  exposed  to  the 
air,  it  loses  its  pungent  odour,  and  a  white  friable  mass  re- 
mains, which  is  the  bicarbonate  of  ammonium,  or  carbonate 
of  water  and  oxide  of  ammonium  :  HO  .  COg  +  NH^O .  COg. 
This  is  a  stable  salt,  and  may  be  dissolved  and  crystallised 
without  change. 

The  sesquicarbonate  of  ammonia  of  the  shops  is  a  crystal- 
line transparent  mass,  which  Rose  finds  to  have  generally, 
but  not  always,  the  composition  assigned  to  it  by  Mr.  Phillips, 
or  to  contain  SCOg  with  2NH3  and  2H0.  Rose  is  disposed 
to  consider  it  a  compound  of  anhydrous  carbonate  of  am- 
monia and  bicarbonate  of  oxide  of  ammonium,  or  NH3CO2  + 
(HO  .  CO2  +  NH4O  .  CO,).  Mr.  Scanlan  has  shown  that  a 
small  quantity  of  water  dissolves  out  the  carbonate  from  this 


PHOSPHATES   OF   AMMONIUM.  739 

salt,  and  leaves  the  bicarbonate,  wliicli  is  the  least  soluble.  This 
observation  does  not  prove  the  commercial  salt  to  be  a  me- 
chanical mixture  of  the  two  salts  derived  from  it,  as  many 
undoubted  compounds  of  two  salts  are  decomposed  by  water, 
when  one  of  the  constituent  salts  is  much  more  soluble  than 
the  other.  Another  salt  was  obtained  by  Rose,  in  well- 
formed  crystals,  of  which  the  ammonia  and  carbonic  acid  are 
in  the  proportions  of  the  sesquicarbonate,  but  with  three 
additional  atoms  of  water.  No  fewer  than  twelve  different 
carbonates  of  ammonia  are  described  by  that  chemist.* 

Sulphate  of  Ammonium,  NH^O  .  SO3  +  HO. —  This  is  a 
highly  soluble  salt,  which  possesses  an  atom  of  water  of 
crystallisation,  in  addition  to  the  atom  which  is  essential  to 
its  constitution.  It  appears  also  to  crystallise  without  this 
water. 

Phosphates  of  Ammonium.  —  The  biammoniacal  tribasic 
phosphate,  (2NH4O  .  HO)  .  PO5,  analogous  to  ordinary  phos- 
phate of  soda,  is  obtained  by  decomposing  the  acid  phosphate 
of  lime  with  carbonate  of  ammonium.  It  forms  large  trans- 
parent crystals,  belonging  to  the  oblique  prismatic  system, 
which  effloresce  on  the  surface  when  exposed  to  the  air,  and 
give  off  a  portion  of  their  ammonia,  even  at  ordinary  tempe- 
ratures. The  salt  dissolves  in  4  parts  of  cold,  and  a  smaller 
quantity  of  hot  water.     (Mitscherlich.) 

The  monoammoniacal  phosphate,  (NH4O  .  2H0)  .  PO5,  is 
formed  by  adding  phosphoric  acid  to  the  solution  of  the  pre- 
ceding salt,  till  the  liquid  becomes  slightly  acid.  It  forms 
crystals  belonging  to  the  square  prismatic  system,  and  some- 
what less  soluble  than  the  preceding.     (Mitscherlich.) 

A  basic  phosphate  is  also  formed  by  mixing  a  concentrated 
solution  of  the  biammoniacal  salt  with  ammonia ;  but  it 
quickly  gives  off  ammonia,  and  is  reconverted  into  the  biam- 
moniacal salt. 

*  Scientific  Memoirs,  ii.  98. 


740  AMMONIUM. 

Pyropliosphate  and  Metaphosphate  of  Ammonium  may  also 
be  formed  bj  adding  ammonia  to  the  aqueous  solutions  of  the 
respective  acids  ;  but  they  are  converted  by  evaporation  into 
the  corresponding  tribasic  phosphates.     (Graham.) 

Oxalates  of  Ammonium, — The  neutral  oxalate,  C4(NH4)20g 
(regarding  oxalic  acid  as  a  bibasic  acid,  p.  539),  is  obtained 
by  neutralising  the  aqueous  acid  with*  ammonia.  It  crys- 
tallises in  long  prisms  united  in  tufts  and  belonging  to 
the  right-prismatic  system:  they  contain  2  eq.  of  water, 
which  they  give  off  at  a  moderate  heat.  The  acid  oxalate, 
64(11 .  NH4)0g,  is  precipitated  in  the  crystalline  form,  when 
the  solution  of  the  neutral  salt  is  mixed  with  oxalic,  sulphuric, 
or  hydrochloric  acid.  It  is  much  less  soluble  than  the  neutral 
salt. 

A  superoxalate,  C/H  .  NH4)08  +  C^HgOg,  separates  from 
a  solution  of  equal  parts  of  oxalic  acid  and  the  acid  oxalate, 
in  crystals  resembling  those  of  the  preceding  salt,  and  con- 
taining 4  eq.  of  water. 

Neutral  oxalate  of  ammonium,  when  strongly  heated,  gives 
off  4  at.  water,  and  yields  a  sublimate  of  oxamide  (p.  558) : 

C,N,HgOg  -  4H0  =    C,N,H,0,. 

Neutral  oxalate  Oxamide. 

of  ammonium. 

The  acid  salt,  when  heated,  gives  off  2  at.  water,  and  leaves 
oxamic  acid  (p.  542)  : 

C^NHgOg  -  2H0    =    C.NHgOg. 

Acid  oxalate  of  Oxamic  acid, 

ammonium. 

All  amides  and  amidogen-acids  may,  indeed,  be  regarded 
as  ammonium-salts  minus  water.  But  few  of  them,  however, 
are  produced  by  the  actual  abstraction  of  water  from  the 
corresponding  ammonium-salts ;  they  are  more  generally 
produced  by  the  action  of  ammonia  on  anhydrous  acids,  acid 
chlorides,  or  compound  ethers  (pp.  542,  557,  561). 


LITHIUM.  741 

The  compounds  formed  by  the  action  of  dry  ammonia  on 
the  anhydrous  acids,  sometimes  called  anhydrous  salts  of 
ammonia,  and,  by  H.  Rose,  ammon-salts,  are  all  either  amides 
or   amidogen-acids.      Thus,    2    vols,    ammoniacal  gas,   and 

1  vol.  carbonic  acid,  unite  and  form  the  compound  NH3CO2, 

which,  doubling  the  atomic  weight,  is  carbamide,  Ng  |  A  ^?  or 

2  at.  ammonia  in  which  one-third  of  the  hydrogen  is  replaced 
by  the  biatomic  radical  carbonyl,  C2O2.  With  anhydrous 
sulphuric  acid,  ammonia  forms  two  compounds,  viz.  NH3SO3, 

Rose's  sulph-atammon,  or  sulphamide,  =   Ng]   fr  ^  +  2H0  ; 


and  sidphamic  acid,  l^^R^Sfi^  =  ^ '^^^^^^^^^^^^  Simi- 
larly, with  anhydrous  sulphurous  acid,  ammonia  forms  thion- 
amide,  NH3SO2  =N  2[^^^%  and  thionamic  acid,  NHgSaOe 

-_  •      2V    2     2>'V     2*    [Forthe  amides  ofphosphoricacid,  seepage  695.] 

All  salts  of  ammonium,  heated  with  fixed  caustic  alkalies, 
give  oif  ammonia,  which  may  be  absorbed  by  hydrochloric 
acid,  and  its  quantity  then  determined  either  by  evaporating 
the  solution  of  chloride  of  ammonium  over  the  water-bath, 
or,  more  exactly,  by  precipitation  with  bichloride  of  platinum 
(p.  385). 


LITHIUM. 

Preparation.- — Pure  chloride  of  lithium  is  fused  over  a 
spirit-lamp,  in  a  small  porcelain  crucible,  and  decomposed  by 
a  zinc-carbon  battery  of  four  or  six  cells.  The  positive  pole 
is  a  small  splinter  of  gas-coke  (the  hard  carbon  deposited  in 
the  gas-retorts),  and  the  negative  pole  an  iron  wire  about 

VOL.  IL  3  E 


742  LITHIUM. 

the  thickness  of  a  knitting-needle.*  After  a  few  seconds,  a 
small  silver-white  regulus  is  formed  under  the  fused  chloride, 
round  the  iron  wire  and  adhering  to  it,  and  after  two  or  three 
minutes  attains  the  size  of  a  small  pea.  To  obtain  the  metal, 
the  wire  pole  and  regulus  are  lifted  out  of  the  fused  mass,  by 
a  small,  flat,  spoon-shaped  iron  spatula.  The  wire  may  then 
be  withdrawn  from  the  still  melted  metal,  which  is  protected 
from  oxidation  by  a  coating  of  chloride  of  lithium.  The 
metal  may  now  be  easily  removed  from  the  spatula  with  a 
pen-knife,  after  having  been  cooled  under  rock-oil.  These 
operations  may  be  repeated  every  three  minutes ;  and  thus  an 
ounce  of  the  chloride  may  be  reduced  in  a  very  short  time. 

Lithium,  on  a  freshly-cut  surface,  has  the  colour  of 
silver,  but  quickly  tarnishes  on  exposure  to  the  air,  becom- 
ing slightly  yellow.  It  melts  at  180°  C.  (356°  F.),  and 
if  pressed  at  that  temperature  between  two  glass  plates, 
exhibits  the  colour  and  brightness  of  polished  silver.  It  is 
harder  than  potassium  or  sodium,  but  softer  than  lead,  and 
may,  like  that  metal,  be  drawn  out  into  wire.  It  tears  much 
more  easily  than  a  lead  wire  of  the  same  dimensions.  It  may 
be  welded  by  pressure  at  ordinary  temperatures.  It  swims 
on  rock-oil,  and  is  the  lightest  of  all  known  solids,  its  specific 
gravity  being  only  0-5986.  Taking  the  atomic  weight  at 
6*5,  its  atomic  volume  is  therefore  1*06,  being  nearly  the 
same  as  that  of  calcium. 

Lithium  is  much  less  oxidable  than  potassium  or  sodium. 
It  makes  a  lead-grey  streak  on  paper.  It  ignites  at  a  tempe- 
rature much  higher  than  its  melting  point,  burning  quietly, 
and  with  an  intense  white  light.     It  burns  when  heated  in 

*  The  decomposing  power  of  an  electric  current  depends  chiefly  upon  its 
density,  i.  e.  upon  the  quotient  obtained  by  dividing  the  strength  of  the  current 
by  the  surface  of  the  pole  at  which  the  electrolysis  takes  place.  Thus,  a  current 
of  constant  strength  passed  through  an  aqueous  solution  of  terchloride  of 
chromium,  eliminates,  as  its  density  is  successively  diminished  (or  the  cross- 
section  of  the  reducing  pole  increased),  metallic  chromium,  chromous  oxide, 
chromic  oxide,  and,  lastly,  hydrogen.    (Bunsen,  Fogg.  Ann.  xci.  619.) 


ESTIMATION   OF    LITHIUM.  743 

oxygen,  chlorine,  bromine,  iodine,  or  dry  carbonic  acid,  and 
with  great  brilliancy  on  boiling  sulphur.  When  thrown  on 
water,  it  oxidises,  but  does  not  fuse  like  sodium.  Nitric  acid  acts 
on  it  so  violently,  that  it  melts  and  often  takes  fire.  Strong  sul- 
phuric acid  attacks  it  slowly;  dilute  sulphuric  acid  and  hydro- 
chloric acid,  quickly.  Silica,  glass,  and  porcelain  are  attacked 
by  lithium  at  temperatures  even  below  200°  C.  (Bunsen.*) 

According  to  Dr.  Mallett  f,  the  atomic  weight  of  lithium  is 
6*95  ;  and  accordingly  that  of  sodium  is  exactly  the  mean 
between  those  of  lithium  and  potassium. 

Nitrate  of  Lithia. — This  salt  has  a  strong  tendency  to  form 
supersaturated  solutions.  Above  10°  or  15°  C,  it  crystallises 
in  rhombic  prisms,  resembling  those  of  common  nitre,  but 
below  10°  in  rhorabohedrons ;  both  kinds  of  crystals  are 
deliquescent.  The  crystals  which  separate  from  the  super- 
saturated solution  at  1°  C.  are  slender  needles.  (Kremers.J) 

Phosphate  of  Lithia,  —  According  to  W.  Mayer  §,  the  pre- 
cipitate formed  en  adding  phosphate  of  soda  to  the  solution 
of  a  lithia-salt,  is  not  a  double  phosphate  of  lithia  and  soda, 
as  commonly  supposed,  but  a  tribasic  phos{)hate  of  lithia, 
SLiO.POg.  The  same  precipitate  is  also  produced  when  a 
lithia-salt  is  treated  with  phosphate  of  potash  or  phosphate  of 
ammonia,  mixed  with  free  alkali. 

Estimation  of  Lithium. — This  element,  when  separated  from 
other  metals,  may  be  estimated  in  the  form  of  sulphate  or 
chloride,  in  the  same  manner  as  potassium  or  sodium.  From 
potassium  it  is  separated  by  precipitating  the  latter  with  bi- 
chloride of  platinum  ;  and  from  sodium,  by  converting  the  two 
bases  into  chlorides,  and  treating  the  dried  chlorides,  in  a  well- 
closed  bottle,  with  a  mixture  of  absolute  alcohol  and  ether, 
which,  after  a  few^  days,  dissolves  the  whole  of  the  chloride  of 
lithium,  and  leaves  the  chloride  of  sodium  undissolved. 

*  Ann.  Cli.  Pharm.  xciv.  107  ;  Chem.  Soc.  Qn.  J.  viii.  143. 
t  Sill.  Ann.  J.  [2],  xxii.  349.  %  Pogg.  Ann.  xcii.  520. 

§  Ann.  Ch.  Pharm.  xcviii.  ]  93. 
3  E  2 


744  BARIUM. 


BARIUM. 


Bunsen  has  obtained  this  metal  by  subjecting  chloride 
of  barium,  mixed  up  to  a  paste  with  water  and  a  little 
hydrochloric  acid,  at  a  temperature  of  100°  C,  to  the  ac- 
tion of  the  electric  current,  using  an  amalgamated  platinum 
wire  as  the  negative  pole.  In  this  manner,  the  metal  is  ob- 
tained as  a  solid,  silver-white,  highly-crystalline  amalgam, 
which,  when  placed  in  a  little  boat  made  of  thoroughly  ignited 
charcoal,  and  heated  in  a  stream  of  hydrogen,  yields  barium 
in  the  form  of  a  tumefied  mass,  darkly  tarnished  on  the  sur- 
face, but  often  exhibiting  a  silver-white  lustre  in  the  cavities.* 
Matthiessen  has  obtained  barium  by  a  method  similar  to  that 
adopted  for  strontium  (p.  756),  but  only  in  the  form  of  a 
metallic  powder. 

Binoxide  or  Peroxide  of  Barium, — A  solution  of  this  oxide 
in  dilute  hydrochloric  acid  acts  as  a  reducing  agent  on  various 
metallic  oxides,  a  portion  of  its  oxygen  uniting,  at  the  moment 
of  separation,  with  the  oxygen  of  the  other  metallic  oxide 
(p.  517).  When  peroxide  of  barium  is  introduced  into  a  solu- 
tion of  bichromate  of  potash  acidulated  with  hydrochloric 
acid,  oxygen  is  abundantly  evolved  (its  evolution  being,  how- 
ever, preceded,  in  the  case  of  cold  dilute  solutions,  by  the 
formation  of  a  blue  compound,  first  observed  by  Barreswil, 
and  supposed  by  him  to  be  a  perchromic  acid,  Orfi^) ;  and 
according  to  Brodie's  experiments,  the  reaction,  when  a  great 
excess  of  bichromate  of  potash  is  present,  takes  place  as 
shown  by  the  equation, 

2Cr03  +  4Ba02  =  Cr^Og  +  70  +  4BaO, 

the  chromic  acid  being  reduced  to  sesquioxide  of  chromium. 
The  quantity  of  oxygen  evolved  affords  the  means  of  calcu- 

♦  Pogg.  Ann.  xci.  619. 


CARBONATE    OF    BARYTA.  745 

lating  the  per  centage  of  real  BaOg  in  the  sample  used.  Oxide, 
chloride,  sulphate,  or  carbonate  of  silver  introduced  into  an 
acid  solution  of  a  peroxide  of  barium,  is  partly  reduced  to 
metallic  silver,  the  quantity  of  metal  thus  reduced  being, 
however,  always  less  than  that  which  is  equivalent  to  the 
oxygen  which  exists  in  the  peroxide  together  with  baryta. 
The  quantity  reduced  increases  with  the  amount  of  the  silver 
compound  used,  and  diminishes  as  the  temperature  is  higher. 
A  small  quantity  of  the  silver-compound,  or  of  any  similar 
substance,  is  capable  of  decomposing  a  large  quantity  of  the 
peroxide.  Iodine,  on  the  other  hand,  decomposes  only  an 
equivalent  quantity,  according  to  the  equation, 

BaO^  +  I  =  Bal  -f  O^  (Brodie*). 

[For  the  separation  of  oxygen  from  the  air  by  first  convert- 
ing baryta  into  the  peroxide,  and  then  decomposing  the  latter, 
see  p.  638.] 

Peroxide  of  barium,  heated  over  a  large  spirit-lamp  in  a 
rapid  current  of  carbonic  acid  gas,  becomes  white-hot,  and  at 
the  same  time  small  white  flames  burst  out  from  its  surface, 
probably  arising  from  the  evolution  of  oxygen  from  the  still 
undecomposed  peroxide.  A  similar,  but  much  more  brilliant 
appearance  is  presented  when  the  peroxide  is  heated  in  sul- 
phurous acid  gas.    (Wohler.f) 

Carbonate  of  Baryta^  mixed  with  carbonate  of  lime  and 
charcoal,  and  heated  to  redness  in  a  stream  of  aqueous 
vapour,  is  decomposed,  and  yields  caustic  baryta.  This  pro- 
cess is  recommended  by  JacquelainJ  for  the  preparation  of 
caustic  baryta. 

According  to  Boussingault§,  a  solution  of  chloride  of  ba- 
rium, mixed  with  the  native  sesquicarbonate  of  soda  called 

*  Phil.  Trans.  1850,  759.  f  Ann.  Ch.  Pharm.  Ixxviii.  175. 

X  Ann.  Ch.  Phys.  [3],  xxxii.  421.  §  Ibid.  xxix.  397. 

3  E  3 


746  STRONTIUM. 

Uras,  yields  a  precipitate  of  2Ba0.3C02.  Laurent  assigns  to 
this  precipitate  the  formula  2BaO.  SCOg  +  HO.  H.  Rose*, 
on  the  other  hand,  finds  that  chloride  of  barium  and  bicar- 
bonate of  soda  always  yield  a  precipitate  consisting  merely  of 
BaO .  COj,  and  similarly  with  lime. 

Recently-precipitated  sulphate  of  baryta,  enclosed,  with  a 
solution  of  bicarbonate  of  soda,  or  with  dilute  sulphuric  acid, 
in  a  sealed  glass  tube,  and  heated  for  60  hours  to  250°  C. 
(472°  F.),  dissolves  to  a  slight  extent,  and  separates  out  on 
the  sides  of  the  tube  in  microscopic  crystals,  whose  form 
agrees  with  that  of  heavy  spar.  Pure  water  or  a  solution  of 
sulphide  of  sodium  does  not  perceptibly  dissolve  sulphate  of 
baryta  under  similar  circumstances.    (Senarmont.f) 

Estimation  of  Barium. — Barium  is  almost  always  estimated 
in  the  form  of  sulphate,  the  precipitation  and  filtration  being 
performed  in  the  manner  already  described  for  the  estimation 
of  sulphuric  acid  (p.  686). 

Precipitation  with  a  soluble  sulphate  likewise  serves  to 
separate  barium  from  all  other  metals  except  strontium, 
calcium,  and  lead. 

Barium  is  also  sometimes  estimated  as  carbonate,  beinsr 
precipitated  by  carbonate  of  ammonia  with  addition  of  caustic 
ammonia,  and  the  liquid  boiled  to  render  the  precipitation 
complete.     The  carbonate  is  not  decomposed  by  ignition. 

STRONTIUM. 

Preparation.  —  This  metal  is  also  obtained  by  the  electro- 
lysis of  its  chloride  in  the  fused  state.  A  small  crucible, 
with  a  porous  cell  in  the  middle,  is  filled  with  anhydrous 
chloride  of  strontium,  mixed  with  a  little  chloride  of  ammo- 
nium, and  in  such  a  manner  that  the  level  of  the  fused 
chloride  within  the  cell  may  be  much  higher  than  in  the  cru- 

*  Pogg,  Ann.  Ixxxvi.  293.  f  Ann.  Ch.  Phys.  [3],  xxxii.  129. 


ESTIMATION    OF    STRONTIUM.  747 

cible.  The  negative  pole  placed  in  the  cell  consists  of  a  very 
fine  iron  wire  wound  round  a  thicker  one,  and  then  covered 
with  a  piece  of  tobacco-pipe  stem,  so  that  only  ^th  of  an 
inch  of  it  appears  below ;  the  positive  pole  is  an  iron  cylinder, 
placed  in  the  crucible  round  the  cell.  The  heat  should  be 
regulated  during  the  experiment,  so  that  a  crust  may  form  in 
the  cell ;  the  metal  will  then  collect  under  this  crust  without 
coming  in  contact  with  the  sides  of  the  crucible.  In  this 
manner,  pieces  of  the  metal  weighing  half  a  gramme  are 
sometimes  obtained. 

Strontium  resembles  calcium  in  colour  (p.  749),  being  only 
a  shade  darker  ;  it  oxidises  much  more  quickly  than  that 
metal.  Its  specific  gravity  is  2*5418.  Its  place  in  the  elec- 
trical series,  with  water  as  the  exciting  liquid,  is  as  follows : 

+  - 

K,     Na,     Li,     Ca,     Sr,     Mg,     &c. 

Strontium  burns  like  calcium,  and  acts  similarly  to  it  when 
heated  in  chlorine,  oxygen,  bromine,  or  iodine,  or  on  boiling 
sulphur,  or  when  thrown  on  water  or  acids.    (Matthiessen.*) 

Estimation  of  Strontium,  —  Strontium,  like  barium,  may  be 
estimated  in  the  form  of  sulphate ;  but  as  sulphate  of  stron- 
tia  is  slightly  soluble  in  water,  it  is  necessary,  in  order  to 
ensure  complete  precipitation,  to  add  alcohol  to  the  liquid, 
which  may  be  done  if  there  are  no  other  substances  present 
which  are  insoluble  in  alcohol. 

Generally  speaking,  however,  it  is  better  to  precipitate 
strontium  in  the  form  of  a  carbonate,  by  adding  carbonate  of 
ammonia  and  caustic  ammonia,  and  heating  the  liquid.  The 
precipitation  of  strontia  in  this  form  is  more  complete  than 
that  of  baryta.  The  precipitate  may  be  ignited  on  a  lamp 
without  giving  off  carbonic  acid.  It  contains  59*27  per  cent, 
of  strontium,  and  70*14  of  strontia. 

*  Chem.  Soc.  Qu.  J.  viii.  107. 
3e  4 


748  STRONTIUM. 

The  same  mode  of  precipitation  serves  to  separate  strontia 
from  the  alkalies. 

The  separation  of  strontia  from  baryta  is  best  effected  by 
means  of  hydrofluosilicic  acid,  which  precipitates  barium  in 
the  form  of  a  crystalline  silicofluoride,  leaving  the  strontium 
in  solution.  The  precipitate  must  be  left  to  settle  down  for 
two  or  three  hours ;  and  its  deposition  may  be  accelerated  by 
a  gentle  heat.  It  may  then  be  collected  on  a  weighed  filter, 
washed  with  water,  and  dried  at  100°  C.  The  filtrate  con- 
taining the  strontium  is  then  mixed  with  sulphuric  acid, 
evaporated,  and  ignited,  whereby  it  is  converted  into  sulphate. 

The  quantities  of  barium  and  strontium  in  a  mixture  may 
likewise  be  determined  by  an  indirect  method,  viz.  by  weigh- 
ing them,  first  in  the  form  of  chlorides  or  carbonates,  and 
afterwards  as  sulphates.  Thus,  suppose  them  to  be  first 
precipitated  as  carbonates,  the  united  weight  of  which  is 
found  to  be  w,  then  converted  into  sulphates,  the  weight  of 
which  is  w\  Then,  to  determine  the  quantity  of  baryta,  x, 
and  strontium,  ?/,  in  the  mixture,  we  have  the  equations 


BaC  SrC  BaS  SrS 

Ba  Sr  Ba  Sr 

98-7  73-7  116-7  91-7 

or,    j^x  ^-j^^^y^iv;  -^^^  x  +    ^i:^y=io'. 


A  similar  method  may  be  applied  in  all  cases  in  which  two 
substances  in  a  mixture  can  be  weighed  in  two  distinct  forms. 
Such  methods,  however,  give  exact  results  only  when  the 
quantities  of  the  substances  to  be  determined  are  not  very 
unequal. 


CALCIUM.  749 


CALCIUM. 


Preparation,  —  A  mixture  of  2  at.  chloride  of  calcium  and 
1  at.  chloride  of  strontium,  with  a  small  quantity  of  chloride  of 
ammonium  (this  mixture  being  more  fusible  than  chloride  of  cal- 
cium alone),  is  melted  in  a  small  porcelain  crucible,  in  which  a 
carbon  positive  pole  is  placed,  while  a  thin  harpsichord  wire 
wound  round  a  thicker  one,  and  dipping  only  just  below  the  sur- 
face of  the  melted  salt,  forms  the  negative  pole.  The  calcium 
is  then  reduced  in  beads,  which  hang  on  to  the  fine  wire,  and 
may  be  separated  by  withdrawing  the  negative  pole  every  two 
or  three  minutes,  together  with  the  small  crust  which  forms 
round  it.  A  surer  method,  however  of  obtaining  the  metal, 
though  in  very  small  beads,  is  to  place  a  pointed  iron  wire  so 
as  merely  to  touch  the  surface  of  the  liquid  ;  the  great  heat 
evolved,  owing  to  the  resistance  of  the  current,  causes  the 
reduced  metal  to  fuse  and  drop  off  from  the  point  of  the  wire, 
and  the  bead  is  taken  out  of  the  liquid  with  a  small  iron 
spatula.  Or,  thirdly,  the  disposition  of  the  apparatus  may  be 
the  same  as  that  for  the  reduction  of  strontium  (p.  746). 

Properties. — Calcium  is  a  light  yellow  metal,  of  the  colour 
of  gold  alloyed  with  silver  ;  on  a  freshly  cut  surface,  the  lustre 
somewhat  diminishes  the  yellow  colour,  which  becomes  more 
apparent  when  the  light  is  reflected  several  times  from  two 
surfaces  of  calcium,  or  when  the  surface  is  slightly  oxidised. 
It  is  about  as  hard  as  gold,  very  ductile,  and  may  be  cut, 
filed,  or  hammered  out  into  plates  having  the  thickness  of 
the  finest  paper.  Its  specific  gravity  is  1*5778.  In  dry  air 
the  metal  retains  its  colour  and  lustre  for  a  few  days,  but  in 
damp  air  the  whole  mass  is  slowly  oxidised.  Heated  on 
platinum-foil  over  a  spirit-lamp,  it  burns  with  a  very  bright 
flash.  It  is  not  quickly  acted  upon  by  dry  chlorine  at  ordi- 
nary temperatures ;  but  when  heated,  burns  in  that  gas  with 


750  CALCIUM. 

a  most  brilliant  light ;  also  in  iodine,  bromine,  oxygen,  sul- 
phur, &c.  With  phosphorus,  it  combines  without  ignition, 
forming  phosphide  of  calcium.  Heated  mercury  dissolves  it 
as  a  white  amalgam.  Calcium  rapidly  decomposes  water, 
and  is  still  more  rapidly  acted  on  by  dilute  nitric,  hydro- 
chloric, and  sulphuric  acids,  nitric  acid  often  causing  ignition. 
Strong  nitric  acid  does  not  act  upon  it  below  the  boiling  heat. 
In  the  voltaic  circuit,  with  water  as  the  liquid  element,  cal- 
cium is  negative  to  potassium  and  sodium,  but  positive  to 
magnesium.  It  is  not,  however  reduced  by  potassium  or 
sodium  from  its  chloride  by  electrolysis.  On  the  contrary,  a 
fused  mixture  of  CaCl  with  KCl  or  NaCl,  in  certain  pro- 
portions, yields  potassium  or  sodium,  when  subjected  in  a  cer- 
tain manner  to  electric  action  (p.  730) ;  hence  it  appears  that 
the  metal  formerly  obtained  by  reducing  chloride  of  calcium 
with  potassium  or  sodium,  could  not  be  calcium,  but  was, 
probably,  a  mixture  of  potassium  or  sodium  with  aluminium, 
silicon,  &c.     (Matthiessen.*) 

Lime,  — According  to  Wittsteinf,  1  part  by  weight  of  lime 
dissolves  in  729  to  723  pts.  of  water,  at  ordinary  temperatures, 
and  in  1310  to  1569  pts.  of  boiling  water.  The  carbonate  of 
lime  deposited  from  lime-water  on  exposure  to  the  air  is 
really  the  neutral  carbonate,  CaO  .  COg. 

Marchand  and  Scheerer  find  that  calcspar  begins  to  give 
off  carbonic  acid  at  200°  C,  but  that  a  certain  quantity  of 
that  acid  remains  with  the  lime,  even  after  the  most  violent 
ignition.J 

Sulphate  of  Lime  dissolves  in  water  containing  sal-ammo- 
niac more  abundantly  than  in  pure  water,  part  of  it  appearing 
to  be  decomposed  into  chloride  of  calcium  and  sulphate  of 
ammonia.  The  presence  of  nitrate  of  potash  likewise  in- 
cceases  the  solubility  of  gypsum.     (A.  Yogel,  jun.§) 


*  Chem.  Soc.  Qu.  J.  viii.  28.  f  Repert.  Pharm.  [3],  i.  182. 

X  J.  pr.  Chem.  1.  237.  §  Repert.  Pharm.  [3],  v.  342. 


ESTIMATION   OF   CALCIUM.  751 

Sulphate  of  Lime  and  Potash,  KO .  SO3  +  CaO .  SO3  +  HO. 
— This  salt  is  obtained  as  an  accessory  product  in  the  manufac- 
ture of  tartaric  acid  from  cream  of  tartar.  The  latter  salt  is 
converted,  bj  treatment  with  carbonate  of  lime,  into  tartrate  of 
lime  and  neutral  tartrate  of  potash  ;  and  by  the  action  of  sul- 
phate of  lime,  all  the  tartaric  acid  is  obtained  in  combination 
with  lime,  together  with  an  impure  solution  of  sulphate  of 
potash.  This  solution,  when  evaporated,  yields  a  hard  depo- 
sit, and  in  slowly  evaporating  large  quantities  of  it,  transparent 
laminated  crystals  are  obtained,  having  the  composition  ex- 
pressed by  the  above  formula ;  they  are  sparingly  soluble  in 
water,  more  easily  in  dilute  hydrochloric  acid.  The  non- 
crystalline deposit  contains  about  Q5  per  cent,  of  this  double 
salt,  together  with  sulphate,  carbonate,  and  phosphate  of 
lime,  carbonate  of  magnesia,  silicate  of  potash,  oxide  of  iron, 
alumina,  water,  and  traces  of  organic  matter.  (J.  A.  Phillips.*) 

Phosphate  of  Lime.  —  According  to  H.  Ludwigf,  the  preci- 
tate  produced  by  ordinary  phosphate  of  soda  in  a  solution  of 
chloride  of  calcium  mixed  with  ammonia,  has,  after  washing 
and  drying  in  the  air,  the  composition  3CaO  .  PO5  +  5|-H0 ; 
after  keeping  for  two  years  in  a  loosely  stoppered  bottle,  it  is 
reduced  to  3CaO .  PO5  +  S^-HO,  and  of  these  3iH0,  2\  go 
off  below  100°.  The  precipitate  was  free  from  chlorine,  but 
contained  a  trace  of  ammonia. 

According  to  Forchhammerij:,  apatite  may  be  artificially 
crystallised  by  fusing  tribasic  phosphate  of  lime,  or  bone-ash, 
with  four  times  its  weight  of  chloride  of  sodium,  and  leaving 
the  fused  mass  to  cool  slowly.  The  mass  when  cold  exhibits 
cavities  containing  numerous  delicate  six-sided  prisms,  having 
the  composition  of  apatite. 

Estimation  of  Calcium. — The  metal  may  be  estimated  either 
as  carbonate  or  as  sulphate.     The  best  method  of  precipitating 

*  Chem.  Soc.  Qti.  J.  iii.  348.  f  Pharm.  Centr.  1852,  345. 

X  Pogg.  Ann.  xci.  588. 


752  CALCIUM. 

it  is,  in  most  cases,  by  means  of  oxalate  of  ammonia,  the 
oxalate  being  the  least  soluble  of  all  the  salts  of  calcium.  If 
the  solution  contains  an  excess  of  any  strong  acid,  such  as 
nitric  or  hydrochloric  acid,  it  must  be  neutralised  with  am- 
monia before  adding  the  oxalate  of  ammonia,  because  oxalate 
of  lime  is  soluble  in  the  stronger  acids.  The  precipitate, 
after  being  washed  with  hot  water  and  dried,  is  heated  over 
a  lamp,  care  being  taken  not  to  allow  the  heat  to  rise  above 
redress.  It  is  thereby  converted  into  carbonate  of  lime,  con- 
taining 40-15  p.  c.  of  calcium  and  56-12  of  lime. 

If,  however,  the  solution  contains  any  acid  which  forms 
with  lime  a  compound  insoluble  in  water,  phosphoric  or 
boracic  acid  for  example,  this  method  of  precipitation  cannot 
be  adopted ;  because,  on  neutralising  with  ammonia,  the  lime 
would  be  precipitated  in  combination  with  that  acid,  and 
would  not  be  converted  into  oxalate  on  addition  of  oxalate  of 
ammonia.  In  such  a  case,  the  lime  may  be  precipitated  as 
sulphate  by  adding  pure  dilute  sulphuric  acid  and  alcohol. 
The  sulphate,  when  dried,  contains  41*25  per  cent,  of  lime. 
Phosphate  of  lime  may,  however,  be  precipitated  from  its 
acid  solutions  by  oxalate  of  ammonia,  with  addition  of  acetate 
of  ammonia,  because  oxalate  of  lime  is  insoluble  in  acetic 
acid,  which  dissolves  the  phosphate  with  facility. 

From  the  alJcalies,  lime  is  easily  separated  eitlier  by  oxalate 
of  ammonia,  or  by  sulphuric  acid  and  alcohol. 

Lime  is  separated  from  baryta  by  precipitating  both  the 
earths  as  carbonates,  dissolving  the  carbonates  in  nitric  acid, 
evaporating  to  dryness,  and  digesting  the  residue  in  absolute 
alcohol,  which  dissolves  nitrate  of  lime,  but  not  nitrate  of 
baryta.  They  may  also  be  separated  in  this  manner  in  the 
form  of  chlorides,  but  the  separation  is  less  complete,  because 
chloride  of  barium  is  not  quite  insoluble  in  absolute  alcohol. 

From  strontia,  lime  is  separated  in  the  same  manner, 
nitrate  of  strontia  being  likewise  insoluble  in  alsolute  alcohol. 

When  baryta,  strontia,  and  lime  occur  together,  the  baryta 


MAGNESIUM.  753 

is  first  separated  by  hydro-fluosilicic  acid ;  the  strontia  and 
lime  in  the  filtrate  are  then  converted  into  sulphates ;  these 
sulphates,  after  being  weighed,  converted  into  carbonates  by 
fusion  vidth  carbonate  of  soda,  or  by  boiling  with  the  aqueous 
solution  of  that  salt  (p.  598);  the  carbonates  weighed;  and  the 
quantities  of  strontia  and  lime  determined  from  the  equations  : 


91-7 
51-7^ 

+ 

68 
28 

y 

= 

w 

73-7 
51-7  "^ 

+ 

50 

28 

y 

= 

w'; 

in  which  x  is  the  weight  of  strontia,  y  that  of  the  lime,  w 
that  of  the  sulphates,  and  w^  that  of  the  carbonates  of  the 
two  bases.  Or  the  carbonates  may  be  dissolved  in  nitric  acid, 
and  the  nitrates  separated  by  absolute  alcohol. 


MAGNESIUM. 

Bunsen  prepares  this  metal  by  the  electrolysis  of  the  fused 
chloride.  A  porcelain  crucible  is  divided  in  its  upper  part 
into  two  halves  by  a  vertical  diaphragm  (made  out  of  a  thin 
porcelain  crucible-cover),  and  fitted  with  a  cover  (filed  from 
a  tile),  through  which  the  extremities  of  the  carbon-poles  of 
a  galvanic  battery  are  introduced  into  the  two  halves  of  the 
crucible.  The  crucible  is  then  heated  to  redness,  together 
with  the  cover  and  the  poles ;  filled  with  fused  chloride  of 
magnesium  (I.  595)  ;  and  subjected  to  the  action  of  a  battery 
of  10  zinc-carbon  elements.  The  negative  pole  is  cut  like  a 
saw,  so  that  the  magnesium,  as  it  separates,  may  lodge  in  the 
cavities,  and  not  float  on  the  surface  of  the  specifically  heavier 
liquid.*  According  to  Matthiessen  f,  the  metal  may  be  much 
more  easily  obtained  from  a  fused  mixture  of  4  at.  chloride 
of  magnesium  and  3  at.  chloride  of  potassium,  which  is  pre- 

*  Ann.  Ch.  Pharm.  82,  137.  f  Chem.  Soc.  Qu.  J.  viii.  107. 


754  MAGNESIUM. 

pared  with  more  facility  than  the  pure  anhyorous  chloride  of 
magnesium.  The  two  salts  mixed  in  the  proper  proportions* 
with  a  little  chloride  of  ammonium  may  be  fused  and  elec- 
trolysed in  Bunsen's  apparatus  just  described,  the  cutting  of 
the  negative  pole  being,  however,  dispensed  with,  as  the 
metal  is  heavier  than  the  fused  mixture.  A  very  simple  and 
convenient  way  of  reducing  the  metal,  especially  for  the 
lecture-table,  is  to  fuse  the  mixture  in  a  common  clay  tobacco- 
pipe  over  an  argand  spirit-lamp  or  gas-burner,  the  negative 
pole  being  an  iron  wire  passed  up  the  pipe-stem,  and  the 
positive  a  piece  of  gas-coke,  just  touching  the  surface  of  the 
fused  chlorides.     (Matthiessen.) 

Magnesium  may,  however,  be  obtained  in  much  larger 
quantity,  by  heating  a  mixture  of  600  grammes  of  chloride 
of  magnesium,  100  grms.  fused  chloride  of  sodium,  and  100 
grms.  of  pulverised  fluoride  of  calcium,  with  100  grms.  of 
sodium,  to  bright  redness,  in  a  covered  earthen  crucible.  The 
magnesium  is  thereby  obtained  in  globules,  which  are  after- 
wards heated  nearly  to  whiteness  in  a  boat  of  compact  char- 
coal placed  within  an  inclined  tube  of  the  same  material, 
through  which  a  stream  of  dry  hydrogen  is  passed.  The 
magnesium  then  volatilises  and  condenses  in  the  upper  part 
of  the  tube.  Lastly,  it  is  remelted  with  a  flux  composed  of 
chloride  of  magnesium,  chloride  of  sodium,  and  fluoride  of 
calcium,  and  is  thus  obtained  in  large  globules.  (H.  Deville 
and  Caron.f) 

Magnesium  on  the  recently  fractured  surface  is  sometimes 
slightly  crystalline  and  coarsely  laminated  ;  sometimes  fine- 
grained. In  the  former  cases  it  is  silver- white  and  shining ;  in 
the  latter,  bluish  grey  and  dull.  Its  specific  gravity  is  1-7430 
at  H-  5°  C.  (Bunsen);  1-75,  according  to  Deville  and  Caron. 
It  is  about  as  hard  as  calcspar,  and  may  be  easily  filed,  bored, 
sawn,  and  flattened  to  a  certain  extent,  but  is  scarcely  more  duc- 

*  The  solution  of  the  chloride  of  magiiesium  mny  be  evjiporated  almost  to 
dryness  and  analysed  to  find  the  pioportiun  of  anhydrous  salt  present. 
t  Ann.  Ch.  Pharm.  ci.  359. 


ESTIMATION    OF    MAGNESIUM.  755 

tile  than  zinc  at  ordinary  temperatures.  It  melts  at  a  moderate 
red  heat  (Bunsen) ;  melts  and  volatilises  at  about  the  same  tem- 
perature as  zinc  (Deville  and  Caron).  It  does  not  alter  in  a 
dry  atmosphere,  but  in  damp  air  soon  becomes  covered  with 
a  film  of  hydrate  of  magnesia.  Heated  to  redness  in  the  air, 
or  in  oxygen  gas,  it  burns  with  a  dazzling  white  light,  and 
forms  magnesia.  It  decomposes  pure  cold  water  but  slowly, 
acidulated  water  very  quickly ;  when  thrown  on  aqueous 
hydrochloric  acid,  it  takes  fire  momentarily  ;  strong  sulphuric 
acid  dissolves  it  but  slowly ;  a  mixture  of  sulphuric  acid  and 
fuming  nitric  acid  does  not  act  upon  it  at  ordinary  temper- 
atures. It  burns  when  heated  in  chlorine  gas ;  also  in 
bromine-vapour,  though  with  less  facility  ;  in  sulphur  and 
iodine- vapour  very  brilliantly  (Bunsen). 

Estimation  of  Magnesium.  —  When  magnesia  occurs  in  a 
solution  not  containing  any  other  fixed  substance,  its  quantity 
may  be  determined  by  evaporating  to  dryness,  igniting  the 
residue,  then  moistening  it  with  sulphuric  acid  slightly  diluted 
with  water,  and  expelling  the  excess  of  that  acid  at  a  low  red 
heat ;  sulphate  of  magnesia  then  remains,  containing  33*7  per 
cent,  of  magnesia. 

If  the  solution  contains  other  fixed  substances,  the  magnesia 
must  be  precipitated  by  the  addition  of  ammonia  in  excess 
and  phosphate  of  soda.  The  precipitated  ammoniomagnesian 
phosphate  is  then  treated  in  the  manner  described  at  p.  700, 
The  pyrophosphate  of  magnesia  obtained  by  igniting  it  contains 
36  33  per  cent,  of  magnesia. 

From  baryta  and  strontia,  magnesia  is  separated  by  sulphuric 
acid ;  from  lime,  by  oxalate  of  ammonia,  with  addition  of  chlo- 
ride of  ammonium  to  prevent  the  precipitation  of  the  magnesia. 

From  the  alkalies,  magnesia  may  be  separated  by  con- 
verting the  bases  into  sulphates,  and  adding  baryta-water. 
The  magnesia  is  then  precipitated  in  the  form  of  hydrate, 
together  with  sulphate  of  baryta.  The  precipitate,  after 
washing,  is  digested  with  dilute  sulphuric  acid,  which  extracts 


756  ALUMINIUM. 

the  magnesia  in  the  form  of  sulphate ;  and  the  filtrate  con- 
taining the  alkalies  together  with  the  excess  of  baryta,  is 
also  treated  with  sulphuric  acid,  which  precipitates  the  baryta, 
and  converts  the  alkalies  into  sulphates. 


ALUMINIUM   OR   ALUMINUM. 

Preparation,  —  This  metal  is  now  obtained  in  considerable 
quantity  by  decomposing  the  chloride  or  fluoride  with  sodium. 
The  chloride  of  aluminium  is  prepared  on  the  large  scale  by 
passing  chlorine  over  a  previously  ignited  mixture  of  clay  and 
coal-tar  in  retorts  like  those  used  in  the  preparation  of  coal- 
gas,  and  is  either  made  to  pass  into  a  chamber  lined  with 
plates  of  earthenware,  where  it  condenses  into  a  compact 
crystalline  mass ;  or  the  vapour  is  made  to  pass  over  chloride 
of  sodium  at  a  red  heat,  whereby  it  is  converted  into  the 
double  chloride  of  aluminium  and  sodium.  To  effect  the 
reduction,  400  pts.  of  this  double  salt,  200  pts.  of  chloride  of 
sodium,  200  pts.  of  fluor-spar  (or  better,  of  cryolite),  all  per- 
fectly dry  and  finely  pounded,  are  mixed  together,  and  the 
mixture  placed,  together  with  75  or  80  parts  of  sodium,  in  an 
earthern  crucible,  the  saline  mixture  and  the  sodium  being 
deposited  in  alternate  layers.  The  crucible  is  then  moderately 
heated  till  the  action  begins,  afterwards  to  redness,  the  melted 
mass  stirred  with  an  earthenware  rod,  and  afterwards  poured 
out.  Twenty  parts  of  aluminium  are  thus  obtained  in  a  com- 
pact lump,  and  about  5  parts  in  globules  encrusted  with  a 
grey  mass.    (H.  Ste-Claire  Deville.*) 

Aluminium  may  also  be  prepared  in  a  similar  manner  from 
cryolite,  the  native  fluoride  of  aluminium  and  sodium  which 
is  now  imported  in  large  quantities  from  Greenland.  (H. 
Rose.f)     Instead  of  this  natural  mineral,  an  artificial  cry- 

•  Ann.  Ch.  Phys.  [3],  xlvi.  415  ;  see  also  Compt.  rend,  xxxviii.  279 ;  xl. 
1298. 
t  ^^SS'  Ann.  xcvi.  152. 


ALUMINIUM.  757 

blite  may  be  used,  jrepared  by  mixing  1  part  of  burnt  clay 
with  3  parts,  or  rather  more,  of  anhydrous  carbonate  of  soda, 
supersaturating  the  mixture  with  hydrofluoric  acid,  then  dry- 
ing and  fusing  it  at  a  red  heat.  A  fluoride  of  aluminium  and 
potassium  possessing  analogous  properties  may  be  prepared  by 
a  similar  process.     (Deville.*) 

Aluminium  may  likewise  be  obtained  by  the  electrolysis  of 
the  double  chloride  of  aluminium  and  sodium,  the  process 
being  similar  to  that  adopted  by  Bunsen  for  the  electrolysis 
of  chloride  of  magnesium.     (Deville,  Bunsen.) 

Pure  aluminium  is  a  white  metal,  with  a  faint  bluish  irides- 
cence ;  when  recently  fused,  it  is  soft  like  pure  silver,  and  has 
a  density  of  2*56  ;  but  after  hammering  or  rolling,  it  is  as  hard 
as  iron,  and  has  a  density  of  2*67.  A  bar  of  it  is  very  sonorous. 
It  conducts  electricity  eight  times  as  well  as  iron,  and  ia 
slightly  magnetic.  Its  melting  point  is  between  those  of  zinc 
and  silver:  when  solidified  from  fusion,  or  reduced  by  electro- 
lysis, it  exhibits  crystalline  forms,  apparently  regular  octo- 
hedrons.  It  does  not  oxidise  in  the  air,  even  at  a  strong  red 
heat ;  neither  does  it  decompose  water,  excepting  at  the 
strongest  red  heat,  —  and  even  then  but  slowly.  It  does  not 
dissolve  in  nitric  acid,  either  dilute  or  concentrated,  at  ordinary 
temperatures,  and  but  very  slowly  in  boiling  nitric  acid ;  dilute 
sulphuric  acid  scarcely  attacks  it  at  ordinary  temperatures, 
even  after  a  long  time ;  but  hydrochloric  acid,  at  any  degree 
of  concentration,  dissolves  it  readily,  even  at  low  temperatures, 
with  evolution  of  hydrogen.  It  is  not  attacked  by  hydrosul- 
phuric  acid,  or  by  the  fused  hydrates  of  the  alkalies.  It  does 
not  combine  with  mercury,  and  when  fused  with  lead,  takes 
up  only  traces  of  that  metal.  With  copper  it  unites  in  various 
proportions,  forming  light,  very  hard,  white  alloys,  and  it 
combines  also  with  silver  and  iron.     (Deville.) 

*  Ann.  Ch.  Phys.  [3],  xlix.  83. 
VOL.  IL  3  F 


758  ALUMINIUM. 

Alumina.  —  The  specific  gravity  of  alumina  ignited  over  a 
spirit-lamp  is  from  3*87  to  3*90 ;  after  6  hours'  ignition  in  an 
air-furnace,  3*75  to  3*725  ;  and  after  ignition  in  a  porcelain 
furnace,  3  999,  which  agrees  very  nearly  with  that  of  naturally 
crystallised  alumina  as  it  occurs  in  the  ruby,  sapphire,  and 
corundum.     (H.  Rose.*) 

Bihydrate  of  Alumina,  soluble  in  ivater,  Alfi^  +  2 HO. 
When  a  dilute  solution  of  biacetate  of  alumina  (see  page  760), 
is  exposed  to  heat  for  several  days,  the  whole  of  the  acetic 
acid  appears  to  become  free,  and  the  alumina  passes  into 
an  allotropic  state  in  which  it  is  soluble  in  water,  and  is  no 
longer  capable  of  acting  as  a  mordant,  or  of  entering  into 
any  definite  combination.  This  allotropic  alumina  retains 
2  at.  water  when  dried  at  100°  C.  Its  solution  is  coagulated 
by  mineral  acids  and  by  most  vegetable  acids,  by  alkalies,  by 
a  great  number  of  neutral  salts,  and  by  decoctions  of  dye- 
woods.  It  is  insoluble  in  the  stronger  acids,  but  soluble  in 
acetic  acid,  unless  it  has  been  previously  coagulated  in 
the  manner  just  mentioned.  Boiling  potash  changes  it  into 
the  ordinary  terhydrate.  Its  coagulum  with  dye-woods  has 
the  colour  of  the  infusion,  but  is  translucent,  and  entirely 
different  from  the  dense  opaque  cakes  which  ordinary  alumina 
forms  with  the  same  colouring  matters.     (Walter  Crum.f) 

According  to  Phillips  J,  hydrate  of  alumina  when  kept 
after  precipitation  in  a  moist  atmosphere  or  under  water, 
becomes  after  a  few  days  difficult  to  dissolve  in  acids. 

Alum,  —  By  fusing  ignited  alumina  with  four  times  its 
weight  of  bisulphate  of  potash,  a  mass  is  obtained,  which 
when  treated  with  warm  water,  leaves  an  insoluble  residue, 
consisting  of  thin  microscopic  six-sided  tables,  which  refract 
light  singly.  They  contain  23  per  cent,  potash,  30*7  sulphu- 
ric acid,  and  46*3  alumina,  and  appear  to  consist  of  crystallised 
anhydrous  alum.     (Salm-Horstmar.§) 

*  Pogg.  Ann.   Ixxiv,  430.  f  Chcm.  Soc.  Qu.  J.  vii.  225. 

t  Chcm.  Gaz.  1848,  319.  §  J.  pr.  Clioni.  lii.  319. 

II  Sill.  Am.  J.  [2],  ix.  30. 


ACETATES  OF  ALUMINA.  759 

Nitrate  of  Alumina,  —  According  to  Ordway||,  a  concen- 
trated and  somewhat  acid  solution  of  alumina  in  nitric  acid,  de- 
posits colourless,  flattened,  oblique  rhombic  prisms,  containing 
AI2O3.3NO5  4  18H0.  These  crystals  melt  at  72-8''  C.  into 
a  colourless  liquid  which  solidifies  in  the  crystalline  form  on 
cooling ;  they  are  deliquescent,  and  dissolve  in  water  and  in 
nitric  acid.  Half  an  ounce  of  the  pulverised  crystals  mixed 
with  an  equal  weight  of  bicarbonate  of  ammonia,  lowered  the 
temperature  from  10*5''  to  —  23*3°  C.  By  the  action  of  this  salt 
upon  hydrate  of  alumina,  basic  salts  appear  to  be  formed. 
Salm-Horstmar*,  by  evaporating  and  cooling  a  solution  of 
hydrate  of  alumina  in  nitric  acid  of  26*3  per  cent,  likewise 
obtained  a  salt  which  crystallised  in  rhombic  prisms  and  (by 
truncation)  in  hexagonal  tables  ;  but  after  repeated  solution  in 
water,  it  no  longer  crystallised  distinctly ;  and  its  aqueous 
solution  was  decomposed  by  evaporation  at  a  somewhat  ele- 
vated temperature. 

Acetates  of  Alumina. — By  decomposing  tersulphate  of 
alumina  (I.,  p.  605),  with  neutral  acetate  of  lead,  a  solution  is 
formed,  consisting  apparently  of  a  mixture  of  biacetate  of 
alumina  with  1  at.  free  acetic  acid. 

When  this  aluminous  solution  is  evaporated  at  a  low  tem- 
perature and  with  sufficient  rapidity,  —  as  by  spreading  the 
concentrated  solution  very  thinly  over  sheets  of  glass  or  porce- 
lain, exposing  it  to  a  temperature  not  exceeding  100°  F., 
and,  as  it  runs  together  in  drops,  rubbing  it  constantly  with  a 
platinum  or  silver  spatula,  —  a  dry  substance  is  obtained 
which  may  be  redissolved  easily  and  entirely  by  water.  This 
is  the  biacetate  of  alumina,  AlgOg  .  2C4H3O3  +  4HO :  the 
alumina  contained  in  it  retains  all  its  usual  properties. 

When  the  first  aluminous  solution,  containing  not  less  than 
4  or  5  per  cent,  of  alumina,  is  left  for  some  days  in  the  cold, 
a  salt  is  deposited  in  the  form  of  a  white  crust,  which  is  an 
allotropic  biacetate  of  alumina  insoluble  in  water.     Heat  effects 

*  J.  pr.  Chem.  Hx.  208. 
3f  2 


760  ALUMINIUM. 

the  same  change  in  the  aluminous  solution  more  rapidly,  and 
the  insoluble  biacetate  then  separates  in  the  form  of  a  granular 
powder.  At  the  boiling  temperature,  the  liquid  is  thus  de- 
prived, in  half  an  hour,  of  the  whole  of  its  alumina,  which 
goes  down  with  |  of  the  acetic  acid,  leaving  ^  in  tlie  liquid. 

The  soluble  biacetate  of  alumina  is  decomposed  by  heat, 
yielding  the  bihydrate  of  alumina  soluble  in  water  already 
described  (p.  758).  The  insoluble  biacetate  of  alumina,  when 
digested  in  a  large  quantity  of  water,  is  gradually  changed 
into  the  soluble  biacetate,  part  of  which,  however,  is  decom- 
posed during  the  process  into  acetic  acid  and  the  allotropic 
bihydrate  of  alumina. 

The  precipitate  which  is  formed  on  the  application  of  heat 
to  a  mixed  solution  of  acetate  of  alumina  and  sulphate  of 
potash,  and  which  is  soluble  in  cold  acetic  acid,  is  a  bibasic 
sulphate  of  alumina,  2AI2O3  .  SO3  -f-  lOHO. 

Common  salt  added  to  a  solution  of  teracetate  of  alumina 
forms,  on  the  application  of  heat,  a  very  finely  divided  white 
precipitate  containing  44*66  per  cent,  alumina,  21*96  acetic 
acid,  5*51  hydrochloric  acid,  25*90  water,  and  1-97  chloride 
of  sodium.  A  similar  precipitate  is  formed  by  nitrate  of 
potash  (Walter  Crum.*) 

Estimation  of  Alumina,  —  Alumina  is  precipitated  from  its 
solutions  in  the  form  of  hydrate  by  ammonia,  carbonate  of 
ammonia,  or  sulphide  of  ammonium;  the  precipitate  when 
ignited  yields  pure  anhydrous  alumina,  containing  53*26  per 
cent,  of  the  metal. 

Precipitation  with  ammonia  or  sulphide  of  ammonium 
serves  also  to  separate  alumina  from  the  preceding  bases.  In 
thus  separating  it  from  the  alkaline  earths,  care  must  be  taken 
not  to  expose  the  liquid  to  the  air ;  otherwise  carbonic  acid 
will  be  absorbed  by  the  excess  of  ammonia,  and  the  alkaline 
earths  precipitated  as  carbonates.  From  baryta,  alumina  is 
most  readily  separated  by  sulphuric  acid. 

*  Chcm.  Soc.  Qu.  J.  vii.  217. 


GLUCINUM.  761 


GLUCINUM. 


This  metal  and  its  compounds  have  been  minutely  ex- 
amined by  Debray.*  The  metal  may  be  obtained  from  the 
chloride  by  reduction  with  sodium.  It  is  a  white  metal, 
whose  density  is  2*1.  It  may  be^  forged,  and  rolled  into 
sheets  like  gold.  Its  melting-point  is  below  that  of  silver. 
It  may  be  melted  in  the  outer  blowpipe-flame,  without  ex- 
hibiting the  phenomenon  of  ignition  presented  by  zinc  and 
iron  under  the  same  circumstances ;  it  cannot  even  be  set  on 
fire  in  an  atmosphere  of  pure  oxygen,  but  in  both  experiments 
becomes  covered  with  a  thin  coat  of  oxide,  which  seems  to 
protect  it  from  further  change.  It  does  not  appear  to  com- 
bine with  sulphur  under  any  circumstances,  but  unites  directly 
with  chlorine  and  iodine  with  the  aid  of  heat.  Silicon  unites 
readily  with  glucinum,  forming  a  hard  brittle  substance  sus- 
ceptible of  a  high  polish ;  this  alloy  is  always  formed  when 
glucinum  is  reduced  in  porcelain  vessels.  Glucinum  does  not 
decompose  water  at  a  boiling  heat,  or  even  when  heated  to 
whiteness.  Sulphuric  and  hydrochloric  acid  dissolve  it,  with 
evolution  of  hydrogen.  Nitric  acid,  even  when  concentrated, 
does  not  act  upon  it  at  ordinary  temperatures,  and  dissolves 
it  but  slowly  at  a  boiling  heat.  Glucinum  is  not  attacked 
by  ammonia,  but  dissolves  readily  in  caustic  potash. 

I'he  above-mentioned  properties  differ  considerably  from 
those  of  the  metal  which  Wohler  obtained  by  igniting  chloride 
of  glucinum  with  potassium  in  a  platinum  crucible ;  the  metal 
thus  obtained  being  a  grey  powder,  very  refractory  in  the 
fire,  but  combining  with  oxygen,  sulphur,  and  chlorine  much 
more  energetically  than  Debray's  metal.  The  differences 
appear  to  be  due,  partly  to  the  different  states  of  aggregation, 
and  partly  to  the  contamination  of  Wohler's  metal  with 
platinum  and  potassium. 

*  Ann.  Ch.  Tliys.  [3],  xliv.  5. 
3  F  3 


762  GLUCINUM. 

Glucina.  —  Debray  prepares  this  earth  from  the  emerald 
of  Limoges  by  the  following  process.  The  mineral,  finely 
pounded  (levigation  with  water  is  quite  superfluous),  is  fused 
with  half  its  weight  of  quicklime  in  an  air-furnace,  and  the 
glass  thus  obtained  is  treated,  first  with  dilute,  and  then  with 
strong  nitric  acid,  till  it  is  reduced  to  a  homogeneous  jelly. 
The  product  is  then  evaporated  to  dryness,  and  heated  suffi- 
ciently to  decompose  the  nitrates  of  alumina,  glucina,  and 
iron,  and  a  small  portion  of  the  nitrate  of  lime;  and  the 
residue,  consisting  of  silica,  alumina,  glucina,  sesquioxide  of 
iron,  nitrate  of  lime,  and  a  small  quantity  of  free  lime,  is 
boiled  with  water  containing  sal-ammoniac,  which  dissolves 
the  nitrate  of  lime  immediately,  and  the  free  lime  after  a  while, 
with  evolution  of  ammonia.  (If  no  ammonia  is  evolved,  the 
calcination  has  not  been  carried  far  enough  and  must  be 
repeated.)  The  liquid  is  then  decanted  ;  the  precipitate,  after 
thorough  washing,  treated  with  boiling  nitric  acid ;  and  the 
resulting  solution  of  alumina,  glucina,  and  iron  poured  into  a 
solution  of  carbonate  of  ammonia  mixed  with  free  ammonia. 
The  earths  are  thereby  precipitated  without  evolution  of  car- 
bonic acid,  and  the  glucina  redissolves,  after  seven  or  eight 
days,  in  the  excess  of  carbonate  of  ammonia.  As  the  car- 
bonate of  ammonia  may  also  dissolve  a  small  quantity  of  iron, 
it  should  be  mixed  with  a  little  sulphide  of  ammonium  to 
precipitate  the  iron  completely.  Lastly,  the  carbonate  of 
ammonia  is  distilled  off,  and  the  carbonate  of  glucina  which 
remains  yields  pure  glucina  by  calcination. 

Glucina  is  not  hardened  by  heat  like  alumina,  but  merely 
rendered  less  soluble  in  acids.  Ebelmen  has  obtained  it  in 
hexagonal  prisms  by  exposing  a  solution  of  glucina  in  fused 
boracic  acid  to  a  powerful  and  long-continued  heat.  It  may 
be  more  easily  obtained  in  microscopic  crystals,  apparently  of 
the  same  form,  by  decomposing  the  sulphate  at  a  high  tem- 
perature in  presence  of  sulphate  of  potash,  also  by  calcining 
the  double  carbonate  of  glucina  and  ammonia. 


GLUCINA.  763 

Hydrate  of  glucina  dissolves  in  potash  like  alumina,  but 
is  reprecipitated  bj  boiling  when  the  solution  is  diluted  with 
water  to  a  certain  extent.  It  is  likewise  soluble  in  carbonate 
of  potash  or  soda,  sulphurous  acid,  and  bisulphite  of  ammonia. 
When  precipitated  by  ammonia,  especially  from  the  oxalate 
or  acetate,  it  is  completely  redissolved  by  prolonged  ebullition. 

Glucina  was  regarded  by  Berzelius  as  a  sesquioxide,  GlgOj, 
while  Awdejew  and  others  regard  it  as  a  protoxide,  GIO.  The 
latter  formula  appears  preferable,  first  because  it  gives  more 
simple  formulaB  for  the  salts  of  glucina  than  the  former,  and 
secondly,  because  glucina,  on  the  whole,  exhibits  a  closer  re- 
semblance to  known  protoxides,  such  as  magnesia,  than  to 
sesquioxides,  such  as  alumina.  The  greater  simplicity  of  the 
formulaB  derived  from  the  formula  GIO,  will  be  seen  from  the 
following  table : 

Neutral  sulphate  of  glucina    .    •  {  or  Glfd3^s63 +?2H0. 

Sulphate  of  glucina  and  potash  .  {  or  f(KO  ^f^G^^^^^^^ 

Carbonate  of  glucina   and    am-f      3(NH40.C02)  +  4G10.3C02 +  H0 
mouia \or9(NH40.C02)+4Gl203.9C02  +  3HO. 

Oxalate  of  glucina  and  potash     .{^^  ^(KO^So'lffG&'^^SC^^^^ 

The  reasons  which  induced  Berzelius  to  regard  glucina  as 
a  sesquioxide,  were  founded  on  the  resemblance  of  glucina 
and  alumina  in  the  hydrated  state,  from  the  volatility  of  the 
chlorides,  and  from  the  supposed  capability  of  glucina  and 
alumina  to  replace  one  another  in  minerals,  as  in  cymophane 
and  in  emerald.  This  last  point  has  been  completely  settled 
by  the  researches  of  Awdejew  and  of  Damour,  from  which  it 
appears  that  cymophane,  the  native  aluminate  of  glucina,  has 
always  the  same  composition  (GlO.AlgOg),  from  whatever 
locality  it  may  be  derived.  With  regard  to  the  hydrates,  it 
is  true  that  alumina  and  glucina  are  precipitated  under  the 
same  circumstances ;  but  there  the  resemblance  ends.  Glu- 
cina, when  dried  in  the  air,  absorbs  carbonic  acid  and  forms  a 

3  F  4 


764  GLUCINUM. 

carbonate,  which  alumina  does  not.  The  existence  of  a  defi- 
nitely crystallised  carbonate  of  ammonia  and  glucina  (obtained 
by  boiling  a  solution  of  glucina  in  carbonate  of  ammonia,  stop- 
ping the  ebullition  as  soon  as  turbidity  appears,  then  filtering, 
and  adding  alcohol)  constitutes  another  important  difference 
between  that  earth  and  alumina.  The  anhydrous  oxides 
likewise  differ  essentially.  Glucina  volatilises,  like  magnesia, 
without  melting,  whereas  alumina  fuses  under  the  same  cir- 
cumstances. Glucina  cannot  be  fused  with  lime,  like  alu- 
mina, the  presence  of  another  body,  such  as  silica  or  alumina, 
being  required  to  enable  the  fusion  to  take  place.  In  this 
respect  again  glucina  resembles  magnesia.  The  identity  of 
crystalline  form  which  has  been  observed  between  glucina 
and  alumina  is  merely  an  isolated  fact,  which  would  be  im- 
portant if  the  two  bodies  possessed  similar  chemical  properties, 
but  not  otherwise. 

Chloride  of  glucinum  exhibits  at  first  sight  considerable 
resemblance  to  chloride  of  aluminium,  and  is  prepared  in  a 
similar  manner  ;  but  the  resemblance  does  not  go  far.  Chlo- 
ride of  glucinum  is  less  volatile  than  chloride  of  aluminium : 
thus,  when  a  mixture  of  finely  powdered  emerald  and  char- 
coal, made  into  a  paste  with  oil,  is  calcined  in  a  crucible, 
then  powdered,  and  heated  in  a  porcelain  tube  through  which 
chlorine  gas  is  passed,  chloride  of  glucinum  and  chloride  of 
aluminium  are  formed  together ;  but  the  chloride  of  glucinum 
passes  over  first,  and  may  be  separately  condensed.  Chloride 
of  glucinum  is,  in  fact,  about  as  volatile  as  chloride  of  zinc. 
Chloride  of  aluminium  unites  with  the  alkaline  chlorides, 
forming  compounds  which  may  be  called  spinelles,  and  are  re- 
presented by  the  general  formula  MCI  +  AlgClg ;  but  chloride 
of  glucinum  does  not  form  any  similar  compound. 

It  must,  however,  be  remembered  that  glucina  does  not 
exhibit  any  very  close  analogy  to  the  class  of  protoxides. 
It  is  not  isomorphous  with  lime  or  magiiesia.  Cymo[)hanc 
may  be  represented  by  the  general  formula  of  the  spinelles, 


SILICON   AND   HYDROGEN,  765 

GIO .  AI2O3 ;  but  the  dissimilarity  of  its  crystalline  form 
prevents  it  from  being  included  in  that  class  of  minerals. 
The  emerald  also  differs  completely  in  crystalline  form 
from  the  generality  of  silicates  of  the  same  composition, 
whose  general  formula  is  MO.  SiOg  +  M/Og.  SSiOg.  Neither 
is  there  any  greater  analogy  between  the  double  sulphates, 
carbonates,  and  oxalates  of  glucina  and  those  of  lime  or  mag- 
nesia. On  the  whole,  glucina  appears  to  be  intermediate  in 
its  properties  between  the  protoxides  and  sesquioxides. 

Glucina  is  precipitated  from  its  solutions  for  quantitative 
analysis  in  the  same  manner  as  alumina.  From  the  latter  it 
is  separated  by  carbonate  of  ammonia. 


Note  to  Page  675. 


Chloride  of  Silicon  and  Hydrogen,  Si2Cl8 .  2HC1. —  This 
is  the  compound  which  Wohler  and  Buff  obtained  by  heating 
crystalline  silicon  in  a  current  of  dry  hydrochloric  acid  gas. 
It  is  a  colourless,  very  mobile  liquid,  of  sp.  gr.  1*65,  and 
boiling  at  42°  C.  It  has  a  very  pungent  odour,  and  fumes 
strongly  in  the  air.  Its  vapour  is  as  inflammable  as  ether- 
vapour,  and  burns  with  a  faint  greenish  flame,  diffusing 
vapours  of  silica  and  hydrochloric  acid.  When  passed 
through  a  red-hot  tube,  it  is  decomposed,  yielding  hydro- 
chloric acid,  terchloride  of  silicon,  and  a  specular  deposit  of 
amorphous  silicon.  The  compound  is  decomposed  by  water 
with  formation  of  a  corresponding  oxide. 

The  compounds  SigBrg .  2HBr,  and  Sijg.  2HI,  are  obtained 
in  a  similar  manner.  The  former  is  liquid,  the  latter  solid,  at 
ordinary  temperatures. 

Ilydrated  Oxide   of  Silicon, —  81203. 2H0,  is  formed    by 


766  NOTE. 

the  action  of  water  on  either  of  the  preceding  compounds, 
but  most  easily  from  the  chloride.  It  is  a  snow-white  amor- 
phous, very  bulky  powder,  which  floats  on  water.  It  is  in- 
soluble in  all  acids  except  hydrofluoric  acid.  Alkalies,  even 
ammonia,  dissolve  it  readily,  with  evolution  of  hydrogen  and 
formation  of  an  alkaline  silicate. 

It  may  be  heated  to  300°  C.  without  alteration ;  but  at 
higher  temperatures,  it  glows  brightly,  and  gives  off*  sponta- 
neously inflammable  hydrogen  gas  (containing  siliciuretted 
hydrogen). 

A  lower  oxide  of  silicon  (SiO  ?)  and  the  corresponding 
chloride  appear  also  to  exist.* 

*  Ann.  Ch.  Pharm.,  Oct.  1857,  p.  94. 


76  r 


TABLE  A. 


FOR   CONVERTING    FRENCH    DECIMAL    MEASURES    AND   WEIGHTS    INTO    ENGLISH 
MEASURES  AND   WEIGHTS. 


1  Meter 


1-0936331  English  yards. 
3-2808992        „       feet. 
39-37079  „       inches. 


1  Liter  =  0-2209687  Imperial  gallons. 

=  1-7677496        „         pints. 

=  0-35317      cubic  feet. 

=  61-02710         „     inches. 

1  Kilogramme  =  0-0196969  cwt. 

=  2-20606      lb.  (avoird.) 

=  2-68098      lb.  (troy). 


1  Gramme 


15-44242      grains. 


These  values  are  taken  from   the  "  Table  of  Constants "  at  the  end  of  the  Tables   of 
Logarithms  published  by  the  Society  for  the  Diffusion  of  Useful  Knowledge. 

The  Imperial  Gallon  is  equal  to  277-24  cubic  inches,  and  contains  10  lbs.  avoirdupois  of  water 
at  60°  Fahr. 


768 


TABLE   B. 


BABOBIETER   SCALE   IN   MILLIMETERS   AND   INCHES. 


Mm.     In. 

Mm.     In. 

Mm.     In. 

700  =  27-560 

730  =  28-741 

760  =  29-922 

701  =  27-599 

731  =  28  780 

761  =  29-962 

702  =  27-639 

732  =  28-820 

762  =  30-001 

703  =  27-678 

733  =  28-859 

763  =  30-040 

704  =  27-717 

734  =  28-899 

764  =  30-080 

705  =  27-756 

735  =  28-938 

765  =  30-119 

706  =  27-795 

736  =  28-977 

766  =-  30-159 

707  =  27-835 

737  =  29-017 

767  =  30-198 

708  =  27-875 

738  =  29-056 

768  =  30-237 

709  =  27  914 

739  =  29-096 

769  =  30277 

710  =  27-954 

740  =  29-135 

770  =  30-316 

711  =  27-993 

741  =  29-174 

771  =  30-355 

712  =  28-032 

742  =  29-214 

772  =  30-395 

713  =  28-072 

743  =  29-253 

773  =  30-434 

714  =  28-111 

744  =  29-292 

774  =  30-474 

715  =  28-151 

745  =  29-332 

775  =  30-513 

716  =  28-190 

746  =  29-371 

776  =  30-552 

717  =  28-229 

747  =  29-411 

777  =  30-592 

718  =  28-269 

748  =  29-450 

778  =  30-631 

719  =  28-308 

749  =  29-489 

779  =  30-671 

720  =  28-347 

750  =  29-529 

780  =  30-710 

721  =  28-387 

751  =  29-568 

781  =  30-749 

722  =  28-426 

752  =  29-607 

782  =  30-788 

723  =  28-466 

753  =  29-647 

783  =.  30-828 

724  =  28-505 

754  =  29-686 

784  =  30-867 

725  =  28-544 

755  =  29-725 

785  =  30-907 

726  =  28-584 

756  =  29-765 

786  =  30-946 

727  =  28  623 

757  =  29-804 

787  =  30-985 

728  =  28  662 

758  =  29-844 

788  =  31-025 

729  =  28-702 

759  =  29-882 

789  =  31064 

28  inches  =  711-187  millimeters. 

29  „       =  736-587  „ 

30  „       =  761-986  „ 

31  „       =  787-386 


1  millimeter  =  0-03937079  inch.      |       1  inch  =  25-39954  millimeters. 


760 


TABLE   C. 

FOR   CONVERTING   DEGREES   OP   THE   CENTIGRADE   THERMOMETER   INTO 
DEGREES    OF   FAHRENHEIT'S    SCALE. 


Cent 

Fah. 

100°  ...  - 

148-0° 

99  ... 

146-2 

98  ... 

144-4 

97  ... 

142-6 

96  ... 

140-8 

95  ... 

1390 

94  ... 

137-2 

93  ... 

135-4 

92  ... 

1336 

91  ... 

131-8 

90  ... 

1300 

89  ... 

128  2 

88  ... 

126-4 

87  ... 

124-6 

86  ... 

122-8 

85  ... 

121-0 

84  ... 

119-2 

83  ... 

117-4 

82  ... 

115-6 

81  ... 

113-8 

80  ... 

1120 

79  ... 

110-2 

78  ... 

108-4 

77  ... 

106-6 

76  ... 

104-8 

75  ... 

1030 

74  ... 

101-2 

73  ... 

99-4 

72  ... 

97-6 

71  ... 

958 

70  ... 

940 

69  ... 

92-2 

68  ... 

90-4 

67  ... 

88-6 

66  ... 

86-8 

65  ... 

850 

64  ... 

83-2 

63  ... 

81-4 

62  ... 

79-6 

61  ... 

77-8 

60  ... 

76-0 

59  ... 

74-2 

58  ... 

72-4 

57  ... 

70-6 

56  ... 

68-8 

55  ... 

67-0 

54  ... 

65-2 

53  ... 

634 

52  ... 

61-6 

51  ... 

59-8 

Cent. 


Fah. 


50°  ... 

-  58-0° 

49  ... 

56-2 

48  ... 

54-4 

47  ... 

52-6 

46  ... 

50-8 

45  ... 

49-0 

44  ... 

47-2 

43  ... 

45-4 

42  ... 

43-6 

41  ... 

41-8 

40  ... 

40-0 

39  ... 

38-2 

38  ... 

36-4 

37  ... 

34-6 

36  ... 

32-8 

35  ... 

31-0 

34  ... 

29-2 

33  ... 

27-4 

32  ... 

25-6 

31  ... 

23-8 

30  ... 

22-0 

29  ... 

20-2 

28  ... 

18-4 

27  ... 

16-6 

26  ... 

14-8 

25  ... 

13-0 

24  ... 

11-2 

23  ... 

9-4 

22  ... 

7-6 

21  ... 

5-8 

20  ... 

4-0 

19  ... 

2-2 

18  ... 

0-4 

17  ... 

+   1-4 

16  ... 

3-2 

15  ... 

5-0 

14  ... 

6-8 

13  ... 

8-6 

12  ... 

10-4 

11  ... 

12-2 

10  ... 

14-0 

9  ... 

15-8 

8  ... 

17-6 

7  ... 

19-4 

6  ... 

21-2 

5  ... 

230 

4  ... 

24-8 

3  ... 

266 

2  ... 

28-4 

1  ... 

30-2 

Cent. 


Fah. 


0^... 

+  32-0° 

1  ... 

33-8 

2  ... 

35-6 

a  ... 

37-4 

4  ... 

39-2 

5  ... 

41-0 

6  ... 

42-8 

7  ... 

44-6 

8  ... 

46-4 

9  ... 

48-2 

10  ... 

50-0 

11  ... 

51-8 

12  ... 

53-6 

13  ... 

55-4 

14  ... 

57-2 

15  ... 

59-0 

16  ... 

60-8 

17  ... 

62-6 

18  ... 

64-4 

19  ... 

66-2 

20  ... 

68-0 

21  ... 

69-8 

22  ... 

71-6 

23  ... 

73-4 

24  ... 

75-2 

25  ... 

77-0 

26  ... 

78-8 

27  ... 

80  6 

28  ... 

82-4 

29  ... 

84-2 

30  ... 

86-0 

31  ... 

87-8 

32  ... 

89-6 

33  ... 

91-4 

34  ... 

93-2 

35  ... 

95-0 

36  ... 

96-8 

37  ... 

98-6 

38  ... 

100-4 

39  ... 

102-2 

40  ... 

104-0 

41  ... 

105-8 

42  ... 

107-6 

43  ... 

109-4 

44  ... 

111-2 

45  ... 

113-0 

46  ... 

114-8 

47  ... 

116-6 

48  ... 

118-4 

49  ... 

120-2 

770 

TABLE  C— (continued.) 


Cent. 

Fah. 

Cent 

Fah. 

Cent. 

Fall. 

+  50°  .. 

.  +  122-0° 

+  100°  .. 

.  +  212-0° 

+  150°  .. 

.  +  302-0° 

51  .. 

123-8 

101   .. 

.  ■  213-8 

151  .. 

303-8 

52  .. 

125-6 

102   .. 

215-6 

152  .. 

305-6 

53  .. 

127-4 

103   .. 

217-4 

153  .. 

307-4 

54  .. 

129-2 

104   .. 

219-2 

154  .. 

309-2 

55  .. 

131-0 

105   .. 

2210 

155  .. 

311-0 

56  .. 

1328 

106   .. 

222-8 

156  .. 

312-8 

57  .. 

134-6 

107   .. 

221-6 

157  .. 

314-6 

58  .. 

1364 

108  ,. 

226-4 

158  .. 

316-4 

59  .. 

138-2 

109  .. 

228-2 

159  .. 

318-2 

60  .. 

1400 

110  .. 

230-0 

160  .. 

330-0 

61  .. 

141-8 

Ill   .. 

231-8 

161  .. 

321-8 

62  .. 

143-6 

112  .. 

233-6 

162  .. 

323-6 

63  .. 

145-4 

113  .. 

235-4 

163  .. 

325-4 

64  .. 

147-2 

114  .. 

237-2 

164  .. 

327-2 

65  .. 

1490 

115  .. 

239-0 

165  .. 

329  0 

66  .. 

150-8 

116  .. 

240-8 

166  .. 

330-8 

67  .. 

152-6 

117  .. 

242-6 

167  .. 

332-6 

68  .. 

154-4 

118  .. 

244-4 

168  .. 

334-4 

69  .. 

156-2 

119  .. 

246-2 

169  .. 

336-2 

70  .. 

158-0 

120  .. 

248-0 

170  .. 

338-0 

71  .. 

159-8 

121   .. 

249-8 

171  .. 

339-8 

72  .. 

161-6 

122  .. 

251-6 

172  .. 

341-6 

73  .. 

163-4 

123  .. 

253-4 

173  .. 

343-4 

74  .. 

165-2 

124  .. 

255  2 

174  .. 

345-2 

75  .. 

167-0 

125  .. 

257-0 

175  .. 

347-0 

76  .. 

168-8 

126  .. 

258-8 

176  .. 

348-8 

77  .. 

170-6 

127   .. 

260-6 

177  .. 

350-6 

78  .. 

172-4 

128  .. 

262-4 

178  .. 

352-4 

79  .. 

174-2 

129   .. 

264-2 

179  .. 

354-2 

80  .. 

176-0 

130  .. 

266-0 

180  .. 

3560 

81  .. 

177-8 

131   .. 

267-8 

181   .. 

357-8 

82  .. 

179-6 

132  .. 

269-6 

182  .. 

359-6 

83  .. 

181-4 

133  .. 

271-4 

183  .. 

361-4 

84  .. 

183-2 

134  .. 

273-2 

184  .. 

363-2 

85  .. 

185-0 

135  .. 

275-0 

185  .. 

365-0 

86  .. 

186-8 

136  .. 

276-8 

186  .. 

366-8 

87  .. 

188-6 

137   .. 

278-6 

187  .. 

368-6 

88  .. 

190-4 

138   .. 

280-4 

188  .. 

370-4 

89  .. 

192-2 

139  .. 

282-2 

189  .. 

3722 

90  .. 

194-0 

140  .. 

284-0 

190  .. 

374-0 

91   .. 

195-8 

141   .. 

285-8 

191   .. 

375-8 

92  .. 

197-6 

142  .. 

287-6 

192  .. 

377-6 

93  .. 

199-4 

143  ,. 

289-4 

193  .. 

379-4 

94  .. 

201-2 

144  .. 

291-2 

194  .. 

381-2 

95  .. 

203-0 

145  .. 

293-0 

195  .. 

383-0 

96  .. 

204-8 

146  .. 

294-8 

196  .. 

384-8 

97  .. 

206-6 

147   .. 

296-6 

197  .. 

386-6 

98  .. 

208-4 

148  .. 

298-4 

198  .. 

388-4 

99  .. 

210-2 

149   .. 

300-2 

199  .. 

390-2 

TABLE  C- 

-(continued.) 

Cent. 

Fah. 

Cent. 

Fah. 

Cent. 

Fah. 

+  200° 

...  +  392-0° 

+  250°  ... 

+  482-0° 

+  300° 

...  +  572-0° 

201 

393-8 

251   ... 

483-8 

301 

573-8 

202 

395  6 

252   ... 

485-6 

302 

575-6 

203 

397-4 

253  ... 

487-4 

303 

577-4 

204 

399-2 

254  ... 

489-2 

304 

.579-2 

205 

401-0 

255  ... 

491-0 

305 

581-0 

206 

402-8 

256  ... 

492-8 

306 

582-8 

207 

404-6 

257  ... 

494-6 

307 

584-6 

208 

406-4 

258  ... 

496-4 

308 

586-4 

209 

408-2 

259  ... 

498-2 

309 

588-2 

210 

410-0 

260  ... 

500-0 

310 

590-0 

211 

411-8 

261   ... 

501-8 

311 

591-8 

212 

413-6 

262  ... 

503-6 

312 

593-6 

213 

415-4 

263  ... 

505-4 

313 

595-4 

214 

417-2 

264  ... 

507-2 

314 

597-2 

215 

419-0 

265  ... 

5090 

315 

599-0 

216 

420-8 

266  ... 

510-8 

316 

600-8 

217 

422-6 

267  ... 

512-6 

317 

602-6 

218 

424-4 

268  ... 

514-4 

318 

604-4 

219 

426-2 

269  ... 

516-2 

319 

606-2 

220 

428-0 

270  ... 

518-0 

320 

608-0 

221 

4298 

27]   ... 

519-8 

321 

609-8 

222 

431-6 

272  ... 

521-6 

322 

611-6 

223 

433-4 

273  ... 

523-4 

323 

613-4 

224 

435-2 

274  ... 

525-2 

324 

615-2 

225 

437-0 

275  ... 

527-0 

325 

617  0 

226 

438-8 

276  ... 

528-8 

326 

618-8 

227 

440-6 

277  ... 

530-6 

327 

620-6 

228 

442-4 

278  ... 

532-4 

328 

622-4 

229 

444-2 

279  ... 

534-2 

329 

624-2 

230 

446-0 

280  ... 

536-0 

330 

626-0 

231 

447-8 

281  ... 

537-8 

331 

627-8 

232 

449-6 

282  ... 

539-6 

332 

6296 

233 

451-4 

283  ... 

541-4 

333 

631-4 

234 

453-2 

284  ... 

543-2 

334 

633-2 

235 

455-0 

285  ... 

545-0 

335 

635-0 

236 

456-8 

286  ... 

546-8 

336 

'636-8 

237 

458  6 

287  ... 

548-6 

337 

638-6 

238 

460-4 

288  ... 

550-4 

338 

640-4 

239 

462-2 

289  ... 

552-2 

339 

642-2 

240 

464-0 

290  ... 

554-0 

340 

644-0 

241 

465-8 

291   ... 

555-8 

341 

645-8 

242 

467-6 

292   ... 

557-6 

342 

647-6 

243 

469-4 

293  ... 

559-4 

343 

649-4 

244 

471-2 

294  ... 

561-2 

344 

651-2 

245 

473-0 

295  ... 

563-0 

345 

663-0 

246 

474-8 

296  ... 

564-8 

346 

654-8 

247 

476-6 

297  ... 

566-6 

347 

656-6 

248 

478-4 

298  ... 

568-4 

348 

658-4 

249 

480-2 

299  ... 

570-2 

349 

660-2 

772 


TABLE  D. 

COMPARISON   OF   TUB   DEORKES    OF   BAUMe's   HYDROMETER   WITH    THE   REAL 
SPECIFIC   GRAVITIES. 


1.  For  Liquids  heavier  than  Water. 


Degrees. 

Specific  Gravity. 

Degrees. 

Specific  Gravity. 

Degrees. 

Specific  Gravity. 

0 

1-000 

26 

1-206 

52 

1-520 

1 

1-007 

27 

1-216 

53 

1-535 

2 

1-013 

28 

1-225 

54 

1-551 

3 

1-020 

29 

1-235 

55 

1-567 

4 

1-027 

30 

1-245 

56 

1-583 

5 

1-034 

31 

1-256 

57 

1-600 

6 

1-041 

32 

1-267 

58 

1-617 

7 

1048 

33 

1-277 

59 

1-634 

8 

1-056 

34 

1-288 

60 

1-652 

9 

1063 

35 

1-299 

61 

1-670 

10 

1-070 

36 

1-310 

62 

1-689 

11 

1-078 

37 

1-321 

63 

•       1-708 

12 

1-085 

38 

1-333 

64 

1-727 

13 

1-094 

39 

1-345 

65 

1-747 

14 

1-101 

40 

1-357 

66 

1-767 

15 

1-109 

41 

1-369 

67 

1-788 

16 

1118 

42 

1-381 

68 

1-809 

17 

1-126 

43 

1-395 

69 

1-831 

18 

1134 

44 

1-407 

70 

1-854 

19 

1143 

45 

1-420 

71 

1-877 

20 

1-152 

46 

1-434 

72 

1-900 

21 

1-160 

47 

1-448 

73 

1-924 

22 

1169 

48 

1-462 

74 

1  949 

23 

1-178 

49 

1-476 

75 

1-974 

24 

1-188 

50 

1-490 

76 

2  000 

25 

1-197 

51 

1-495 

773 


TABLE  D.  --  (continued). 
2.  Baumi's  Hydrometer  for  Liquids  lighter  than  Water, 


Degrees. 

Specific  Gravity. 

Degrees. 

Specific  Gravity. 

Degrees. 

Specific  Gravity. 

10 

1-000 

27 

0-896 

44 

0-811 

11 

0-993. 

28 

0-890 

45. 

0-807 

12 

0-986 

29  ' 

0-883 

46 

0-802 

13 

0-98Q. 

30' 

0-880,' 

47 

0-798 

14 

0-973 

31 

0-874 

48 

0-794 

15 

0-967 

32  X 

0-869 

49 

0789 

16 

0-960 

33-^. 
34^ 

0-864 

St) 

0-785 

17' 

0-9  54f 

0-859* 

61 

0-781 

1-8 

0-948 

35. 

^     0-854-*,. 

62    ; 

0-777  . 

19 

0-942 

36 

0-840 

5^ 

0-773 

20 

0-93^ 

3> 

0-844"*- 

54 

0-7^8 

21 

0-930 

38 

0-839. 

•55 

0-764 

22 

0-924 

39, 

0-831 

66 

0-760 

23 

0-918 

40 

0-830 

57  ^ 

0-757 

24 

0-913 

41 

0-825 

58 

0-753 

25 

0-907 

42 

0-820 

59 

0-740.. 

26 

0-901 

43 

0-816 

60 

0-743. 

Baume's  hydrometer  is  very  commonly  used  on  the  Continent,  especially  for 
liquids  heavier  than  water. 

In  the  United  Kingdom,  Twaddcll's  hydrometer  is  a  good  deal  used  for  dense 
liquids.  This  instrument  is  so  graduated  that  ihe  real  specific  gravity  can  be 
deduced  by  an  extremely  simple  method  from  the  degree  of  the  hydrometer, 
namely,  by  multiplying  the  latter  by  5,  and  adding  1000  ;  the  sum  is  the  specific 
gravity,  water  being  1000.  Thus  10°  Twaddell  indicates  a  specific  gravity  of 
1050,  or  105  ;  90°  Twaddell,  1450,  or  1-45. 


VOL.   11, 


3  a 


774 


TABLE  E. 

SHOWING    THE    PROPORTION   BY   WEIGHT   OP  ABSOLUTE   OR   REAL    ALCOHOL   IN 
100  PARTS  OP  SPIRITS  OF  DIFFERENT  SPECIFIC  GRAVITIES.     (fOWNES.) 


Sp.  Gr.  at 

Percentage  of 

Sp.  Gr.  at 

Percentage  of 

Sp.  Gr.  at 

Percentage  of 
real  Alcohol. 

60OF. 

real  Alcohol. 

GQOF. 

real  Alcohol. 

60OF. 

•9991 

0-5 

•9511 

34 

•8769 

68 

•9981 

1 

•9490 

35 

•8745 

69 

•9965 

2 

•9470 

36 

•8721 

70 

•9947 

3 

•9452 

37 

•8696 

71 

•9930 

4 

•9434 

38 

•8672 

72 

•9914 

5 

•9416 

39 

•8649 

73 

•9898 

G 

•9396 

40 

•8625 

74 

•9884 

7 

•9376 

41 

•8603 

75 

•9869 

8 

•9356 

42 

•8581 

76 

•9855 

9 

•9335 

43 

•8557 

77 

•9841 

10 

•9314 

44 

•8533 

78 

•9828 

11 

•9292 

45 

•8508 

79 

•9815 

12 

•9270 

46 

•8483 

80 

•9802 

13 

•9249 

47 

•8459 

81 

•9789 

14 

•9228 

48 

•8434 

82 

•9778 

15 

•9206 

49 

•8408 

83 

•9766 

16 

•9184 

50 

•8382 

84 

•9753 

17 

•9160 

51 

•8357 

85 

•9741 

18 

•9135 

52 

•8331 

86 

•9728 

19 

•9113 

53 

•8305 

87 

•9716 

20 

•9090 

54 

•8279 

88 

•9704 

21 

•9069 

55 

•8254 

89 

•9691 

22 

•9047 

56 

•8228 

90 

•9678 

23 

•9025 

57 

•8199 

91 

•9665 

24 

•9001 

58 

•8172 

92 

•9652 

25 

•8979 

59 

•8145 

93 

•9638 

26 

•8956 

60 

•8118 

94 

•9623 

27 

•8932 

61 

•8089 

95 

•9609 

28 

•8908 

62 

•8061 

96 

•9593 

29 

•8886 

63 

•8031 

97 

•9578 

30 

•8863 

64 

•8001 

98 

•9560 

31 

•8840 

65 

•7969 

99 

•9544 

32 

•8816 

66 

•7938 

100 

•9528 

33 

•8793 

67 

INDEX, 


A. 


Absolute  Expansion  of  Mercury,  ii.  4. 
Absorption,  Coefficients  of,  ii,  649. 

of  Gases  by  Liquids,  ii,  647. 
Water,  Heat 

evolved  in  the, 
ii.  633, 
Acetate,  Ferrous,  ii.  43. 

Mercurous,  ii.  303. 
Acetates  of  Alumina,  ii.  759. 
Copper,  ii.  105. 
Lead,  ii.  125. 
Acid,  Anhydrous  Sulphuric,  i.  188. 

Antimonic,  ii.  228. 

Antimonious,  ii.  222. 

Antitartaric,  ii.  478. 

Arsenic,  ii.  207. 

Arsenious,  ii.  203. 

Azophosphoric,  ii.  699. 

Azoto-sulphuric,  i.  412. 

Bismuthic,  ii.  243. 

Bisul-hyposulphuric,  i.  418. 

Boracic,  i.  390  ;  ii.  669. 

Bromic,  i.  490. 

Carbonic,  i.  363. 

Chloric,  i.  129,  473. 

Chlorocarbosulphurous,  ii.  705. 

Chloromethylosulphurous,  ii.  705. 

Chloronitric,  i.  479. 

Chloronitrous,  i.  480. 

Chlorochromic,  ii.  169. 

Chlorosulphuric,  i.   410  ;    ii.   551, 
709. 

Chlorous,  i.  477. 

Chromic,  ii.  163. 

Cobaltic,  ii.  67. 

Columbic,  ii.  289. 

Columbous,  ii.  286. 

Deutazophosphoric,  ii.  699. 

Ferric,  ii.  51. 

Fluoboric,  i.  507. 


Acid,  Fluosilicic,  i.  508, 
Hydriotic,  i.  497. 
Hydrobromic,  i.  489, 
Hydrochloric,  i.  464. 
Hydroferricyanic,  ii.  39. 
Hydroferrocyanic,  ii.  49. 
Hydrofluoric,  i.  504. 
Hydrofluosilicic,  i.  509. 
Hydrotelluric,  ii.  200. 
Hydrosulphuric,  i,  419,  445, 
Hypochloric,  i,  478. 
Hypochlorous,  i.  469. 
Hypoiodic,  ii.  712. 
Hypophosphorous,  i.  434. 
Hyposulphuric,  i.  413. 
Hyposulphurous,  i,  115,  415. 
Iodic,  i.  498. 
Manganic,  ii.  18. 
Mellitic,  Croconic,  Rhodizonic,  L 

371. 
Metaphosphorie,  i.  448  ;  ii,  693, 
Metastannic,  ii.  138. 
Methylosulphurous,  ii.  706. 
Molybdic,  ii.  187. 
Monosul-hyposulphuric,  i.  417. 
Nitric,  i.  346. 
Nitroprussic,  ii.  55. 
Nitrosulphuric,  i.  411. 
Nitrous,  i.  341. 
Osmiamic,  ii.  404. 
Osmic,  ii.  '403. 
Osmious,  ii.  402. 
Oxalic,  i.  372. 
Oxamic,  ii.  740. 
Penta-iodic,  i.  501, 
Pentathionic,  i.  418. 
Perchloric,  i.  115,  475. 
Perchlorocarbosulphurous,  ii.  705. 
Pei'chromic,  ii.  169. 
Periodic,  i.  501. 
Permanganic,  ii.  18. 
Phosphamic,  ii.  697. 


3  o  2 


776 


INDEX. 


Acid,  Phosphoric,  i.  438. 

Phosphoric,  Amides  of,  ii.  695. 
Phosphorous,  i.  434. 
Pyrophosphamic,  ii.  700. 
Racemic,  ii.  477. 
Radicals,  Hydrides  of,  ii.  565. 
Ruthenic,  ii.  416. 
Selenic,  i.  429. 
Selenious,  i.  428. 
Silicic,  i.  396  ;  ii.  677. 
Stannic,  ii.  137. 
Sulpharaic,  ii.  741. 
Sulphuric,  i.  402. 
Sulphurous,  i.  399- 
Sulphantimonic,  ii.  232. 
Tantalic,  ii.  278. 
Tantalous,  ii.  278. 
Thionamic,  ii.  741. 
Telluric,  ii.  198. 
Tellurous,  ii.  196. 
Tetrathionic,  i.  418. 
Titanic,  ii.  147. 
Trisul-hyposulphuric,  i.  418. 
Trithionic,  i.  417. 
Tungstic,  ii.  178. 
Vanadic,  ii.  174. 
Acids,  Action  of  Ammonia  on  Anhydrous, 
ii.  557. 
Anhydrous,  ii.  542. 
Aromatic,  ii.  538. 
Basicity  of,  ii.  536. 
Bibasic,  ii.  538. 
Conjugated,  ii.  541. 
Fatty,  Boiling  Points  of,  ii.  584. 
Fatty,  Table  of,  ii.  538. 
Heat  evolved  in  the  Combination 

of,  with  Water,  ii.  632. 
Monobasic,  ii.  538. 
or  Negative  Oxides,  ii.  535. 
Oxygen,  i.  186. 
Sulphur,  ii.  547. 
Theory  of,  i.  187. 
Tartaric  and  Antitartaric,  ii.  478. 
Tribasic,  ii.  540. 

with    Bases,    Heat   produced   by 
Combination  of,  ii.  631. 
AflSnity,  Chemical,  i.  217  ;  ii.  586. 
of  Solution,  i.  218. 
Order  of,  i.  223. 
Tables  of,  i.  224. 
Air,  Analysis  of,  i.  331. 

Composition  of  dry  Air  by  Volume, 
i.  336. 
Air,  Diffusion  of  Vapours  into,  i.  90. 

Extraction  of  Oxygen  from  Atmo- 
spheric, ii.  638. 
Researches  on  the  Expansion  of,  i. 

13. 
Weight  of,  i.  324. 


Alcohol,  Action  of  Sulphuric  Acid  on,  ii. 

602. 
Alcoholic  Nitrides,  Secondary  and  Ter- 
tiary, ii.  555. 
Sulphides,  ii.  546. 
Alcohol-metals,  derived  from  Type  HH, 

ii.  566. 
Alcohol-radicals,  ii.  518,  531. 

Action   of    Ammonia 
on  the  Bromides  and 
Iodides  of,  ii.  554. 
Chlorides  of,  ii.  548. 
Cyanides  of,  ii.  552. 
Hydrides  of,  ii.  563. 
Primary  Nitrides  of,  ii.  563. 
Alcohols,  Biatomic,  ii.  532. 

Boiling  Points  of,  ii.  583. 
Classification   of   Primary,   ii. 

531. 
Secondary,  or  Ethers,  ii.  534. 
Triatomic,  ii.  533. 
Aldehyde-radicals,  Hydrides  of,  ii.  564. 

Nitrides  of,  ii.  556. 
Aldehydes,  ii.  534. 
Alkalamides,  ii.  561. 
Alkalies,  Estimation  of  in  Silicates,   ii. 
678. 

Separation  of  Magnesia  from, 
755. 
Alkalimetry,  i.  547. 

Gay-Lussac's  Method  of,   i. 
550. 
Allotropy,  i.  176—180. 
Alloys  of  Antimony,  ii.  234. 
Bismuth,  ii.  249. 
Cadmium,  ii.  91. 
Copper,  ii.  106. 
Gold,  ii.  358. 
Lead,  ii.  127. 
Mercury,  ii.  324. 
Nickel,  ii  77. 
Silver,  ii.  343. 
Tin,  ii.  143. 
Zinc,  ii.  87. 
Alum,  i.  606  ;  ii.  758. 
Basic,  i.  608. 
Stone,  i.  607. 
Alumina,  i.  602;  ii.  757. 

Acetates  of,  ii.  759. 

and    Potash,    Sulphate  of,   i. 

117. 
Estimation  and  Separation  of, 

ii.  760. 
Hydrates  of,  i.  603 ;  ii.  758. 
Nitrate  of,  i.  602,  610. 
Phosphate  of,  i,  610. 
Salts  of,  i.  605. 
Silicates  of,  i.  610. 
Silicates  of  Lime  and  of,  i.  316. 


INDEX. 


777 


Alumina,  Sulphate  of,  i.  605. 

and  Potash,  Alum, 
i.  606. 
Aluminium,  i.  601. 

Chloride  of,  i.  604. 
Fluoride  of,  i.  605. 
Preparation  of,  i.  601 ;  ii.  756. 
Properties  of,  i.  601 ;  ii.  757. 
Sulphide  of,  i.  604. 
Sulphocyanide  of,  i.  605. 
Amalgam  of  Gold,  ii.  358. 
Amalgamation  of  Silver,  ii.  328. 

of    the     Zinc    Plate    of 
the  Voltaic  Battery,  j. 
246. 
Amalgams,  ii.  324. 
Amides  of  Phosphoric  Acid,  ii.  695. 
Primary,  ii.  556. 
Secondary,  ii.  559. 
Tertiary,  ii.  560. 
Amido-chloride  Mercuric,  ii.  310. 
Amidogen- Acids,  ii.  542. 
Salts,  ii.  561. 
and  Amides,  i.  204, 
Ammon-compounds,  ii.  741. 
Ammonia,  Action  of,  on  Anhydrous  Acids, 
ii.  557. 
Acid     Chlorides,   ii. 

558. 
Compound     Ethers, 

ii.  557. 
Dichloride    of  Mer- 
j  cury,  ii.  299. 

the  Bromides  and  Io- 
dides  of   the   Al- 
cohol-radicals,    ii. 
554. 
and   Glucina,  Carbonate   of, 

ii.  763. 
Antimoniates  of,  ii.  231. 
Aurate  of,  ii.  351. 
Chromates  of,  ii.  166. 
Estimation  of,  ii.  384,  741. 
Molybdate  of,  ii.  190. 
Nessler's  Test  for,  ii.  317. 
Phosphate  of,  i.  563. 
Preparation  of,  i.  353. 
Properties  of,  i.  355. 
Salts  of,  i.  202, 
Why  is  it  a  Base  ?  i.  207. 
Ammoniacal  Amalgam,  i.  203. 

Compounds  of  Iridium,  ii. 

397. 
Compounds  of  Palladium,  ii. 

388—390. 
Platinum    Salts,    ii.    371 — 

382. 
Salts,   Decomposition  of,  i. 
205. 


Ammoniacal  Salts  of  Cobalt,  ii.  68. 
Ammonia-salts,  Anhydrous,  ii.  741. 
Ammonia  type,  ii.  523,  553. 
Ammonio-Bichloride  of  Tin,  ii.  140. 

Compounds  of  Nickel,  ii.  77. 
Nitrate  of  Silver,  ii.  212,  342. 
Nitrates,  Mercuric,  ii.  322. 
Platinic  Compounds,  ii.  376 — 

378. 
Platinous  Compounds,  ii.  372 

—374. 
Sulphate  of  Copper,  ii.  212. 
Ammonium  and  Bismuth,  Terchloride  of, 
ii.  246. 
Chloride  of,  ii.  736. 
Carbonates  of,  ii.  738. 
Chloroplatinate  of,  ii.  370. 
Nitrate  of,  ii.  738. 
Oxalates  of,  ii.  740. 
Phosphates  of,  ii.  739. 
Sulphate  of,  ii.  739. 
Sulphides  of.  ii.  737. 
Ammo-platamraonium,  Bisalts  of,  ii.  378 
—381. 
Proto-salts  of,  ii. 
375,  376. 
Amphigen,  or  Leucite,  i.  612. 
Amylic  Alcohol,  active  and  inactive,  ii. 

480. 
Analcime,  i.  613. 

Analysis  of  Organic  Bodies,  i.  373  ;  ii. 
662. 
Sea- water,  i.  319. 
Silicates,  ii.  677. 
Volumetric,  Bunscn's  gene- 
ral Method  of,  ii.  722 
Anhydrides,  or  Anhydrous  Acids,  ii.  542. 
Anhydrous  Acids,   Action  of  Ammonia 
on,  ii.  557. 
Nitric  Acid,  ii.  652. 
Sulphuric    Acid,    Formation 

of,  i.  403  ;  ii.  622. 
Sulphuric  Acid,  Action  of,  on 
the  Pentachloride  of  Phos- 
phorus, ii.  551,  709. 
Telluric  Acid,  ii.  199. 
Tellurous  Acid,  ii.  196. 
Animal  Charcoal,  i.  361. 
Anthracite,  i.  358. 

Antidotes  to  Arsenious  Acid,  ii.  217. 
Antimoniate  of  Antimony,  ii.  231. 
Antimoniates  of  Lead,  ii.  231. 

Ammonia,  ii.  231. 
Potash,  ii.  229. 
Antiraonic  Acid,  ii.  228. 
Oxide,  ii.  222. 

Acid,  Action  of,  on  Penta- 
chloride of  Phosphorus,  ii. 
710. 


3  C  3 


778 


INDEX. 


Antimonides,  ii.  562. 
Antiraonious  Acid,  ii.  222. 
Antimoniuretted  Hydrogen,  ii.  233. 
Antimony,  Sources  and  Extraction  of,  ii. 
221. 

Alloys  of,  ii.  234. 
and  Arsenic,  Separation  of,  ii. 
239. 
Potash,  Oxalate  of,  ii.  226. 
Tartrate  of,  ii.  226. 
Tin,  Separation  of,  ii.  238. 
Oxide  of,  ii.  222. 
Pentachloride  of,  ii.  232. 
Pentasulphide  of,  ii.  232. 
Estimation  and  Separation  of, 

ii.  235. 
Separation  of,   from    Arsenic 

and  Tin,  ii.  236. 
Sulphate  of,  ii.  226. 
Terchloride  of,  ii.  225. 
Terfluoride  of,  ii.  225. 
Tersulphide  of,  ii.  223. 
Antitartaric  Acid,  ii.  478. 
Antithetic,  or  Polar  Formula;,  i.  204. 
Aqueous  Vapour,  Tension  of,  i.  435. 
Argentiferous  Copper,  Liquation  of,  ii.  328. 
Aridmm,  ii.  59. 
Arseniate  of  Cobalt,  ii.  65. 

Didymium,ii.  277. 
Uranyl,  ii.  258. 
Arsenic  and  Antimony,  Separation  of,  ii. 
239. 
Hydrogen,  ii.  210. 
Acid,  ii.  207. 

considered  Tribasic,  i.  208. 
Chlorides  of,  ii.  210. 
Estimation  and  Separation  of,  ii. 

217. 
Reduction,  Test  for,  ii.  213. 
Persulphide  of,  ii.  209. 
Separation   of,  from    Antimony 

and  Tin,  ii.  236. 
Sources  and  Extraction  of,  ii.  203. 
Sulphides  of,  ii.   209. 
Testing  for,  ii.  211, 
Arsenides,  ii.  562. 
Arsenious  Acid,  ii.  203. 

Antidotes  of,  ii,  217. 
Ash,  Analysis  of  Black,  i.  560. 
Aspartic  Acid,  active  and  inactive,  ii.  480. 
Assay  of  Gold,  ii.  361. 

Silver,  ii.  346. 
Atmosphere,  i.  324, 327. 

Density  of  the,  i.  325. 
Temperature  of  the,  i.  325. 
Atomic  Motion,  ii.  600. 

Representation  of  a  double  De- 
composition, i.  237. 
Theory,  i.  133. 


Atomic   Volume,    dependent    upon    ra- 
tional Formula,  ii.  580. 
of  Liquids,  ii.  569. 

Solids,  i.   209,  210;  ii. 
582. 
and  Specific  Gravity  of 

Elements,  i.  211. 
of  Salts,  i.  213. 
Oxides,  i.  215. 
"Weights,  Gerhardt's,  ii.  513. 

Relations  between  the, 
and  Volumes  of  Bo- 
dies in  the   Gaseous 
State,  i.  142—148. 
Atoms  and  Equivalents,  ii.  509. 
Specific  Heat  of,  i.  135. 
Table  of  Specific  Heat  of,  i.  136. 
A  urate  of  Potash,  ii.  352. 
Auric  Bromide,  ii.  356. 
Chloride,  ii.  355. 
'  Iodide,  ii.  357. 
Oxide,  ii.  350. 

and     Soda,    Hvposulphite 
of,  ii.  358. 
Sulphide,  ii.  355. 
Aurosulphite  of  Potash,  ii.  352. 
Aurous  Chloride,  ii.  349. 
Oxide,  ii.  349. 

and     Soda,    Hyposulphite 
of,  ii.  357. 
Baryta,  ii.  358. 
Sulphide,  ii.  352. 
Azophosphoric  Acid,  ii.  699. 
Azoto  sulphuric  Acid,  i.  412. 


B. 


Barilla,  i.  562. 
Barium,  i.  575  ;  ii.  744. 

Binoxide  of,  i.  577  ;  ii.  742. 
Chloride  of,  i.  577. 
Class  of  Elements,  i.  169. 
Decomposition  of  Peroxide  of, 

by  Aqueous  Vapour,  ii.  638. 
Estimation  and  Separation  of,  ii. 

746. 
Formation  of  Peroxide  of,  ii.  638. 
Protoxide  of,  i.  575. 
Baryta  and  Aurous  Oxide,  Hyposulphite 
of,  ii.  358. 
Carbonate  of,  i.  577;  ii.  745. 
Chromate  of,  ii.  166. 
Estimation  of,  ii.  746. 
Hydrate  of,  i.  576. 
Molybdate  of,  ii.  191. 
Nitrate  of,  i.  578. 
Sulphate  of,  i.  578. 


INDEX. 


779 


Bases   and  Acids,   Heat  developed  by 
Combination  of,  ii.  631. 
Nitrile,  ii.  555. 

Proper  or  Metallic  Oxides,  ii.  530. 
Basic  Alum,  i.  608. 
Basicity  of  Acids,  ii.  536. 
Basyl   Class  of  Compound   Radicals,  i. 

186. 
Battery,  Bird's,  i.  287. 

Bunsen's,  i.  286. 
Daniell's,  i.  283. 
Grove's,  i.  269,  285. 
Beilstein's  Experiments  on  Liquid  Diffu- 
sion, ii.  612. 
Benzoate  Ferric,  ii.  53. 
Beryl,  or  Emerald,  i.  617. 
Beryllia,  or  Glucina,  i.  616. 
Beryllium,  i.  615. 

Biamides,    Primary,    or    Diamides,    ii. 
558. 

Tertiary,  ii.  561. 
Bi-ammonio-platinic  Compounds,  ii.  378. 

—381. 
Bi-ammonio-platinous     Compounds,    ii. 

375,  376. 
Bibasic  Phosphate  of  Water,  i.  441. 

Salts,  i.  193. 
Biborate  of  Soda,  i.-565. 
Bicarbonate  of  Potash,  i.  533. 

and  Magnesia,   i. 
597. 
Soda,  i.  552. 
Bicarburetted  Hydrogen,  of  Faraday,  i. 
386. 
Preparation 
of,  i.  385. 
Bichloride  of  Bismuth,  ii.  ?45. 
Iridium,  ii.  396. 
Lead,  ii.  118. 
Osmium,  ii.  401. 
Platinum,  ii.  369. 
Tin  with  Oxychloride  of 

Phosphorus,  ii.  142. 
Tin  with  Peutachloride  of 

Phosphorus,  ii.  141. 
Titanium,  ii.  148. 
Tin,  ii.  140. 
Tin    and    Potassium,    ii. 

142. 
Tin  and  Sulphur,  ii.  141. 
Bichromate  of  Bismuth,  ii.  249. 

Chloride  of  Potassium,  ii. 

166. 
Potash,  ii.  165. 
Bifluoride  of  Titanium,  ii.  149. 
Bihydrosulphate  of  Potash,  i.  528. 
Bimcjcurammonium,    Chloride     of,     ii. 
312. 
Nitrate  of,  ii.  324. 


Binoxide  or  Bioxide  of  Barium,  i.  577. 
Hydrogen,  i.  319. 
Manganese  and  Hydrochlo- 
ric Acid,  Preparation  of 
Chlorine  from,  i.  458. 
Nitrogen,  Compound  of,with 
Chlorine,  i.  472. 

Properties  of,   i, 

341. 
Preparation  of,  i. 
341. 
Strontium,  i.  580. 
Cobalt,  ii.  67. 
Bismuth,  ii.  241. 
Iridium,  ii.  395.  * 

Lead,  ii.  115. 
Manganese,  ii.  13,  14. 
Platinum,  ii.  368. 
Ruthenium,  ii.  415. 
Tin,  ii.  136. 
Vanadium,  ii.  173. 
Bird's  Battery  and  Decomposing  Cell,  i. 

287. 
Bi-salts  of  Ammo-platammonium,  ii.  378, 
381. 
Platammonium,  ii.  376,  378. 
Bismuth  and  Ammonium,  Terchloride  of, 
ii.  246. 
Bichloride  of,  ii.  245, 
Bichromate  of,  ii.  249. 
Bioxide  of,  241. 
Bisulphide  of,  ii.  244. 
Carbonate  of,  ii.  249. 
Nitrates  of,  ii.  247. 
Quadroxide  of,  ii,  243. 
Selenide  of,  ii.  24  i. 
Sources   and   extraction  of,  ii. 

239. 
Subnitrates  of,  ii.  247. 
Sulphates  of,  ii.  247. 
Terchloride  of,  ii.  245. 
Teriodide  of,  ii.  246. 
Teroxide  of,  ii.  242. 
Tersulphide  of,  ii.  244. 
Bismuthic  Acid,  ii.  243. 
Bisul-hyposulphuric  Acid,  i.  418. 
Bisulphate  of  Soda,  i.  562. 
Bisulphide  of  Bismuth,  ii.  244. 
Carbon,  i.  425. 

Action  of  Chlorine 

on,  ii.  703. 
Action  of  Nascent 
Hydrogen  on,  ii. 

'685. 
decomposed  by 
heating  with 
Water  and  with 
Sahs  in  sealed 
tubes,  ii.  585, 


3  G  4 


780 


INDEX. 


Bisulphide  of  Hydrogen,  i.  423. 
Iron,  ii.  47. 
Platinum,  ii.  369. 
Titanium,  ii.  148. 
Tin,  ii.  139. 
Bittern,  i.  542. 
Black  Sulphur,  ii.  681. 
Black's  Views  on  Fluidity,  i.  43. 
Bleaching  Powder,  i.  591. 
Bodies,  Compound,  i.  113. 

Relation    between    the    Atomic 
Weights  and  the  Volumes  of, 
in  the  Gaseous  State,  i.  142. 
Boilers,  Construction  of,  i.  61,  62. 
Boiling  Point  and  Chemical  Composition, 
Relations  between,  ii.  583. 
Points  of  Acids,  ii.  583. 

Alcohols,  ii.  583. 
Compound    Ethers,   ii. 

584. 
Homologous  Com- 

pounds, ii.  585. 
Table  of,  i.  52. 
Boracic  Acid,  Estimation  of,  ii.  671. 
Reactions  of,  ii.  669. 
Boracite,  i.  600. 
Borate  of  Magnesia,  i.  599. 
Borates,  i.  391. 
Borax,  i.  565. 

Borofluoride  of  Potassium,  ii.  671. 
Boron,  Chloride  of,  i.  484. 

Allotropic    modifications    of,    ii. 

667. 
Estimation  of,  ii.  671. 
Fluoride  of,  i.  507. 
Nitride  of,  ii.  670. 
its  Preparation,  Properties,  i.  389. 
Boutigny,  Experimeats  on  the  Ebullition 

of  Water,  i.  49. 
Brewster  on  Light,  i.  326. 
Brix,  Experiments  of  Vaporisation  on,  i. 
56,  57. 
on  the  Latent  Heat  of  Vapour  of 
Water,  i.  56. 
Bromic  Acid,  i.  490. 
Bromide,  Auric,  ii.  356. 

Mercuric,  ii.  315. 

Mercurous,    or   Dibromide    of 

Mercury,  ii.  300. 
of  Alcohol-radicals,  Action  of 
Ammonium,  ii.  554. 
Cadmium,  ii.  91. 
Iodine,  i.  502. 
Lead,  ii.  119. 
Nitrogen,  ii.  711. 
Phosphorus,  i.  491. 
Silver,  ii.  338. 
Silicon,  i.  491. 

and  Hydrogen,  ii.  765. 


Bromide  of  Sulphur,  i.  490. 

Tantalum,  ii.  284. 
Titanium,  ii.  149. 
Bromides,  ii.  552. 

Atomic  Volume  of  Liquid,  ii. 
577. 
Bromine,  Chloride  of,  i.  490. 

Preparation  of,  i.  488. 
Properties  of,  i.  489. 
Separation  of  from  Chlorine,  ii. 
717. 
Iodine,     ii. 
719. 
Volumetric    Estimation  of,  ii. 
724. 
Bude  Light,  Gurney's,  i.  384. 
Bunsen,  Carbo-zinc  Battery,  i.  286. 
Eudiometers,  i.  381. 
Experiments  on  the  Absorption 

of  Gases,  ii.  647. 
Experiments    on   the   influence 
of  Mass  on  Chemical  Action, 
ii.  587. 
General  Method  of  Volumetric 

Analysis,  ii.  722. 
and  Roscoe,  Measurement  of  the 
chemical  action  of  Light,  489. 
Burette,  Description  of,  i.  551. 
Bussy,  Table  of  the  Efficiency  of  different 
Charcoals,  i.  361. 


Cadmium,  Alloys  of,  ii.  92. 

Chloride,  Bromide,  Iodide,  and 

Sulphate  of,  ii.  91. 
Estimation  and  Separation  of, 

ii.  92. 
Oxide,  ii.  90. 

Sources  and  Extraction  of,  ii.  98. 
Sulphide  of,  ii.  90. 
Calcium,  i.  581,  593. 

Binoxide,  Protosulphide,  Phos- 
phide, Chloride  of,  i.  584-85. 
Estimation  of,  ii.  752. 
Fluoride  of,  i.  586. 
Hydrate  of  the  Binoxide  of,  i. 

584. 
Preparation  and  Properties  of, 

ii.  749. 
Separation  of,  from  Barium  and 

Strontium,  ii.  752. 
Separation  of,  from  Magnesium, 
and  the  Alkali-metals,  ii.  752, 
755. 
Calomel,  Dichloride  of  Mercury,  or  Mer- 
curous Chloride,  ii.  298. 


INDEX. 


781 


Caloric,  i.  1. 
Calorimeters,  ii.  626. 
Canary-glass,  Fluoresence  of,  ii.  257,  484. 
Capillary  Tabes,  i.  15. 
Carbamide,  ii.  558,  741. 
Oarbides,  i.  362. 

Carbon  and  Hydrogen,  Compounds  of,  i. 
374. 
Nitrogen,  Cyanogen,  i.  387. 
Sulphur,  i.  425. 
Bisulphide    of,    i.  425;    ii.   685, 

703. 
Chlorides  of,  i.  481. 
Class  of  Elements,  i.l74. 
from  Wood,  i.  360. 
Estimation    of,    by   Combustion 
with  Oxide  of  Copper,  &c.  ii. 
662. 
Hydrogen,  and  Oxygen,  Atomic 
Volume  of  Liquids  containing, 
ii.  37. 
Perchloride  of,  i.  483. 
Protochloride  of,  i.  483. 
Protosulphide  of,  ii.  684. 
Relation  between  Heat  of  Com- 
bustion and  Specific  Heat  of, 
ii.  629. 
Solid  Sulphide  of,  i.  427. 
Specific  Heat,  and  Heat  of  Com- 
bustion of  Varieties  of,  i.  139; 
ii.  629. 
Subchloride  of,  i.  483. 
Sulphides  of,  i.  425;  ii.  684,  685. 
Sulphite  of  Perchloride  of,ii.  703. 
Sulphite  of  Protochloride  of,  ii. 

704. 
Uses  of,  i.  363. 
Volatility  of,  ii.  656. 
Carbonate  of  Baryta,  i.  577;  ii.  745. 
Bismuth,  ii.  247. 
Cerous,  ii.  265. 
Chromous,  ii.  155. 
Mercurous,  ii.  301. 
of  Cobalt,  ii.  63. 
Copper,  ii.  101. 
Didymium,  ii.  275. 
Glucina,  ii.  763. 
Glucina  and  Potash,  ii.  763. 
Iron,  ii.  41. 
Lanthanum,  ii.  271. 
Lead,  ii.  119. 
Lime,  i.  587. 
Lithia,  i.  574. 
Magnesia,  i.  596. 
Manganese,  ii.  8. 
Potash,  i.  532. 
Silver,  ii.  339. 
Soda,  i.  544. 

Hydrates  of,  ii.  732. 


Carbonate  of  Soda,  Preparation  of,  from 
theSulphate,  i.  557. 
Solubility  of,  ii.  733. 
Strontia,  i.  580. 
Zinc.  ii.  85. 
Carbonates,  i.  368. 

Decomposition  of  insoluble, 
by   soluble   Sulphates,  ii. 
597. 
Decomposition    of     insolu- 
ble Salts  by  Alkaline,  ii. 
597. 
of  Ammonium,  ii.  738. 
Table  of,  i.  213. 
Carbonic  Acid,  Composition  of,  i.  366. 
Estimation  of,  ii.  663. 
Preparation  of,  i.  363. 
Properties  of,  i.  364. 
Uses  of,  i.  368. 
Vapour,    Tension    of,   i. 
73. 
Oxide,   absorption  of    by  Di- 
chloride  of  Copper, 
ii.  661. 
Estimation  of,  ii.  664. 
Preparation,  i.  369. 
Properties,  i.  370. 
Carburet  of  Iridium,  ii.  397. 
Carburets  or  Carbides,  i.  362. 
Cast-iron,  ii.  28. 
Catalysis  or  Decomposition  by  contact, 

i.  233. 
Cavendish,   Experiments    on  Hydrogen, 

i.  311. 
Celsius's  Thermometer,  i.  18. 
Ceric  Oxide,  ii.  264. 
Cerium,  ii.  261. 

Estimation  and   Separation    of, 

ii.  267. 
Metallic,  ii.  263. 
Protochloride  of,  ii.  265. 
Protofluoride  of,  ii.  265. 
Protosulphide  of,  ii.  264. 
Protoxide  of,  ii.  263. 
Sesquichloride  of,  ii.  265. 
Sesquioxide  of,  ii.  263. 
Cerous  Carbonate,  ii.  265. 
Oxalate,  ii.  265. 
Oxide,  ii.  263. 
Phosphate,  ii.  266. 
Sulphate,  ii.  266. 
Ceruse,  ii.  119. 
Chalybeate  Waters,  i.  319. 
Charcoal,  i.  358. 

Animal,  i.  361. 
as  a  Disinfectant,  ii.  659. 
Platinised,  ii.  660. 
Chemical  Action,  Development  of  Heat 
by,  ii.  625. 


782 


INDEX. 


Chemical  Action,  Influence  of  Mass  on, 
ii.  586. 
of    Light,    Measure- 
ment of,  ii.  489. 
Chemical  Affinity,  i.  217;  ii.  586. 

and  Magnetic  Actions  of  the 

Current  compared,  ii.  499. 
and  Optical  Extinction  of  the 

Chemical  Rays,  ii.  495. 
Composition  and  Boiling  Point, 

Relations  between,  ii.  583. 
Composition  and  Density,  Re- 
lations between,  ii.  669. 
Compounds,  Classification  of, 

ii.  527. 
Decomposition,  Cold  produced 

by,  ii.  635. 
Functions,     Classification     of 
Bodies  according  to  their, 
ii.  528. 
Nomenclature,  i.  117. 
Notation  and  Classification,  i. 

108;  ii.  509. 
Rays,  Extinction  of,  ii.  495. 
Chlorate  of  Lead,  ii.  124. 

Potash,  i.  537. 
Chlorates,  i.  474. 
Chloric  Acid,  i.  473. 

Composition  of,  i.  474. 
Resolution    of,    into    Per- 
oxide of  Chlorine   and 
Hyperchloric    Acid,    i. 
475. 
Chloride,  Auric,  ii.  355. 
Aurous,  ii.  349. 
Chromic,  ii.  159. 
Chromous,  ii.  154. 
Cupric,  ii.  101. 
Cuprous,  ii.  97. 
Ferric,  ii.  490. 
Ferrous,  ii.  48. 
Mercuric,  ii.  308. 
Mercurous,  ii.  298. 
Platinic,  ii.  369. 
Platinous,  ii.  367. 
Stannic,  ii.  140. 
Stannous,  ii.  133. 
Uranous,  ii.  254. 
of  Aluminium,  i.  604. 
Ammonium,  ii.  736. 
Barium,  i.  577. 
Bimercurammonium,  ii.  312. 
Boron,  i.  484. 
Bromine,  i.  490. 
Cadmium,  ii.  91. 
Calcium,  i.  595. 
Carbon,  i.  431. 
Cobalt,  ii.  62. 
Didymium,  ii.  274. 


Chloride  of  Gold,  ii.  349. 

and  Potassium,  ii.  356. 
Iodine,  i.  502. 
Lanthanum,  ii.  271. 
Lead,  ii.  117. 
Lime,  i.  591. 

Volumetric      Estima- 
tion of,   i.  592;   ii. 
726. 
Magnesium,  i.  595. 
Mercurammonium,  ii.  312. 
Mercury  with  Ammonia,  ii. 

309. 
Mercury,  Double  Salts  of,  ii. 

313. 
Nickel,  ii.  76. 
Nitrogen,  i.  480;  ii.  702. 
Phosphorus,  i.  487. 
Phosphoryl,  ii.  551. 
Potassium,  i.  528. 

Bichromate  of,  ii. 
166. 
Rhodium  and  Potassium,  ii. 

410. 
Silicon,  i.  484. 

and  Hydrogen,  ii.  765. 
Silver,  ii.  336. 
Sodium,  i.  542. 
Strontium,  i.  580. 
Sulphuryl,  ii.  550,  709. 
Tantalum,  ii.  283. 
Tetramercurammonium,     ii. 

312. 
Thionyl,  ii.  708. 
Uranyl,  ii.  256. 

and    Potassium,    ii. 
257. 
Zinc,  ii.  84. 
Chlorides,  i.  123,  463;  ii.  548. 

Acid  or  Negative,  ii.  549. 
Action    of  Ammoniaon  Acid, 

ii.  558. 
and    Oxides   of    Osmium,    ii. 

400. 
Atomic  Volume  of  Liquid,  ii. 

577. 
Basic  Metallic,  ii.  548. 
Classification  of,  ii.  548. 
of  Alcohol-Radicals,  ii.  549. 
Tables  for  Atomic  Volumes  of 
1st  and  2nd  Class  of,  i.  214, 
215. 
of  Arsenic,  ii.  210. 
Bibasic  Acids,  ii.  539. 
Iridium,  ii.  396. 
Manganese,  ii.  7,  12,  21. 
Palladium,  ii.  387,  388. 
Platinum,  ii.  367,  3G9. 
Tellurium,  ii.  200. 


INDEX. 


783 


Chlorides  of  Tribasic  Acids,  ii.  540. 

Tungsten,  ii.  183. 
Chlorimetry,  i.  592. 
Chlorine,  i.  114,  455. 

Action  of,  on  Potash,  i.  473. 
and  Binoxide  of  Nitrogen,  i.  479. 
Oxygen,  Compounds  of,  i. 

469. 
Sulphur,  i.  485. 
Class  of  Elements,  i.  171. 
Estimation  of,  ii.  716. 
Heat  of  Combination  of  Metals 

-with,  ii.  630. 
Peroxide  of,  i.  478. 
Preparation  of,  i.  456. 
Process  for,  from  Hydrochloric 
Acid  and  Binoxide  of  Man- 
ganese, i.  458. 
Process  for,  from  Chloride  of 
Sodium,  Binoxide  of  Manga- 
nese, and  Sulphuric  Acid,  i. 
460. 
Properties  of,  i.  460. 
Separation  of,  from  Iodine,  ii. 

719. 
Uses  of,  i.  462. 

Volumetric    Estimation   of,   ii. 
724. 
Chlorite  of  Lead,  ii.  124. 
Chlorites,  Volumetric  Estimation  of,  ii. 

725. 
Chlorocarbosulpliurous  acid,  ii.  705. 
Chlorochromic  Acid,  ii.  169. 
('hloromethylosulphurous  Acid,  ii.  705. 
Chloronitric  Acid,  i.  479. 
Chloronitrous  Acid,  i.  480. 
Chlorophosphate  of  Lead,  ii.  125. 
Chlorophosphide  of  Nitrogen,  ii.  710. 
Chloroplatinate  of  Ammonium,  ii.  370. 
Potassium,  ii.  370. 
Sodium,  ii.  370. 
Chloroplatinite  of  Po- 
tassium, ii.  368. 
Chlorosulphide  of  Phosphorus,  i.  487;  ii. 
707. 
Tin,  ii.  140. 
Chlorosulphuric  Acid,  i.  410;  ii.  550,  709. 
Chlorous  x\cid,  i.  477. 
Chloroxicarbonic  Gas,  i.  484. 
Chloroxide  of  Phosphorus,  i.  ^187. 
Chromate  of  Baryta,  ii,  166. 
Lead,  ii.  167. 
Lime,  ii.  167. 
Magnesia,  ii.  167. 
Potash,  ii.  165. 
Silver,  ii.  168. 
Soda,  ii.  166. 
Chromates  and  Tungstates,  Table  of,  i. 
214. 


Chromates,     Compounds    of     Mercuric 
Chloride  with  Alkaline, 
ii.  31.5. 
Decomposition  of  Insolu- 
ble,  by  Alkaline   Car- 
bonates, ii.  599. 
of  Ammonia,  ii.  1 66. 
Volumetric  Estimation  of, 
ii.  726. 
Chrome  Iron,  ii.  162. 
Chromic  Acid,  ii.  163. 

Chloride,  ii.  159. 
Oxide,  ii.  155. 
Salts,  Reactions  of,  ii.  1 56. 
Sulphate,  ii.  159. 
Chromium  and  Potassium,  Oxalate  of,  ii. 
161. 
Estimation    and    Separation 

of,  ii.  1 69. 
Protochloride  of,  ii.  154. 
Protoxide  of,  ii.  1 53. 
Sesquichloride  of,  ii.  159. 
Sesquioxide  of,  ii.  155. 
Sesquisulphide  of,  ii.  159. 
Sources   and   Extraction   of, 

ii.  152. 
Terfluoride  of,  ii.  169. 
Chromoso-chromic  Oxide,  ii.  155. 
Chromous  Carbonate,  ii.  155. 
Chloride,  ii.  154. 
Oxide,  ii.  153. 
Sulphate,  ii.  155. 
Sulphite,  ii.  155. 
Chrysoberyl,  i.  617. 
Cinnabar,  ii.  307. 
Circular  Polarisation,  ii.  464. 

in  Organic  Bodies,  ii.  468. 
Claudet,  Analysis  of  Black  Ash,  i.  560. 
Clay,  i.  610,  614. 

Iron  Stone,  Smelting  of,  ii.  25. 
Classification    and    Notation,    Chemical, 
ii.  509. 
of  Bodies  according  to  their 
Chemical   Functions,  ii. 
527. 
of  Elements,  i.  168. 
Coal  Gas,  i.  378. 

Henry's  Analysis  of,  i.  880. 
Cobalt,  Ammoniacal  Salts  of,  ii.  68. 
Arseniate  of,  ii.  65. 
Bioxide  of,  ii.  67. 
Carbonate  of,  ii.  63. 
Estimation  and  Separation  of,  ii. 

73. 
Chloride  of,  ii.  62. 
Nitrate  of,  ii.  63. 
Phosphate  of,  ii.  65. 
Phosphide  of,  ii.  67. 
Protoxide  of,  ii.  6L 


784 


INDEX. 


Cobalt,  Separation  of,  from  Nickel,  ii.  78. 
Sesquicyanide  of,  ii.  67. 
Sesquioxide  of,  ii.  65. 
Sources  and  Extraction  of,  ii.  59. 
Sulphide  of,  ii.  67. 
Cobaltic  Acid,  ii.  67. 
Oxide,  ii.  65. 
Cobaltous  Oxide,  ii.  61. 
Cobalt-yellow,  ii.  63. 
Coefficients  of  Diffusion,  ii.  612. 

Gas-absorption,  ii.  648. 
Cohesion,  i.  217. 

Axes  of,  in  Wood,  ii.  444. 
Cold  produced  by  Chemical  Decomposi- 
tion, ii.  635. 
Columbic  Acid,  ii.  289. 
Columbium,  ii.  285. 
Columbous  Acid,  ii.  286. 
Columbites,  ii.  288. 
Coloured   Media,  Spectra  exhibited  by, 

ii.  487. 
Combining  Measure,  i.  145. 
Numbers,  ii.  510. 
Proportions,  i.  121 — 132. 
Combustion,  Heat  of,  i.  299;  ii.  625. 

in  Air,  i.  301. 
Common  Salt,  i.  542. 
Compound  Ethers,  ii.  545. 

Action  of  Ammonia  on,  ii.  557. 
Boiling  Points  of,  ii.  584. 
Compounds,  Formation  of,  by   Substitu- 
tion, i.  227. 
Formula}  of,  i.  118. 
Condensing  Tube,  i.  63. 
Conduction  of  Heat,  i   28;  ii.  441. 
Conjugate  Metals,  ii.  568. 

Kadicals,  ii.  527. 
Conjugated  Acids,  ii.  541. 
Contraction  of  Liquids  from  the  Boiling 
Point,  i.  7  ;  ii.  424. 
Water,  i.  9. 
Copper,  Acetates  of,  ii.  105. 

Action    of    Nitric    Acid    upon, 

i.  341. 
Alloys  of,  ii.  107. 
Ammonio-sulphate  of,  ii.  212. 
and  Potash,  Oxalate  of,  ii.  105. 
Diohloride  of,  ii.  97. 
Dicyanide  of,  ii.  97. 
Diniodide  of,  ii.  97. 
Dioxide  of,  ii.  95. 
Disulphide  of,  ii.  96. 
Esfimation  and    Separation    of, 

ii.  107. 
Hydride  of,  ii.  96. 
Liquation  of  Argentiferous,    ii. 

328. 
Nitrates  of,  ii.  105. 
Protochloride  of,  ii.  101. 


Copper,  Protoxide  of,  ii.  99. 

Sources   and   Extraction  of,   ii. 

92. 
Sulphate  of,  ii.  103. 
Volumetric  Estimation  of,  ii.  108. 
Cordier,  Investigation  on  Heat,  i.  40. 
Corrosive  Sublimate,  ii.  308. 
Crichton's  Thermometer,  i.  17. 
Cryophorus,  Dr.  Wollaston's,  i.  66. 
Crystalline  Form  and    Rotatory  Power, 

Relations  between,  ii.  476. 
Crystallised  Bodies,  Conduction  of  Heat 

in,  ii.  441. 
Cupellation  of  Silver,  ii.  346. 
Cuprammonium,  i.  203;  ii.  102. 
Cuproso-cupric  Cyanide,  ii.  98. 
Cuprous  Chloride,  Iodide,  and  Cyanide, 
ii.  97. 

Hyposulphite,  ii.  98. 
Oxide,  ii.  95. 
Carbonate,  ii.  102. 
Chloride,  ii.  101. 
Nitrate,  ii.  105. 
Oxide,  ii.  99. 
Salts,  Reactions  of,  ii.  99. 
Sulphate,  ii.  105. 
Sulphite,  ii.  98. 
Current,  Heating  Power  of  the  Voltaic, 
ii.  506. 

Reduction  of  the  Force  of  the, 
to  absolute  Mechanical  Mea- 
sure, ii.  506. 
Regulator,  ii.  504. 
Electric,    Measurement    of,    ii. 
496. 
Cyanide,  Cuproso-cupric,  ii.  98. 
Cuprous,  ii.  97. 
Ferric,  ii.  48. 
of  Lead,  ii.  119. 
Mercury,  ii.  318. 
Mercury   and   Potassium,  ii. 

320. 
Palladium,  ii.  387. 
Potassium,  i.  530. 
Silver,  ii.  339. 
Cyanides,  Compound,  i.  200. 

of   the     Alcohol-radicals,    ii. 

552. 
of  Platinum,  ii.  368,  379. 
Cyanogen,  i.  337. 


D. 


Dalton  on  Evaporation  of  Water,  i.  91. 
Dalton's  Atomic  Theory,  i.  133. 

Law  of  the  Dilatation  of  Gases, 
i.  12. 

Miscibility  of  Gases,  i.  85. 


INDEX. 


785 


Daniell's  Constant  Battery,  i.  285. 
Hygrometer,  i.  95. 
Pyrometer,  i.  20. 
Debus'  Experiments  on  the  Influence  of 

Mass  on  Chemical  Action,  ii.  590. 
Decomposition,  i.  225. 

by  Contact,  i.  233. 

Cold     produced    by,     i. 

635. 
Circumstances  which  af- 
fect the  order  of,  ii.  225 ; 
ii.  591—604. 
Decompositions,  Secondary,  i.  262. 
Delarive  and  Marcet,   Haycraft,  Dulong, 
Apjohn,  Suermann,  Delaroche,  Berard, 
on  Specific  Heat  of  Gases,  i.  26. 
Density  and  Chemical  Composition,  Re- 
lations between,  ii.  569. 
Deutazophosphoric  Acid,  ii.  699. 
Deuto-hydrate    of  Phosphoric    acid,    i. 

441. 
Dew,  Deposition  of,  i.  38. 

Well's  Experiments  on,  i.  39. 
Diamagnetic  Bodies,  i.  282. 
Diamides,    or     Primary    Biamides,     ii. 

558. 
Diamond,  i.  357. 

-boron,  ii.  668. 
-silicon,  ii.  673. 
Diaphragm,   Two    Polar    Liquids   sepa- 
rated by  a  Porous,  i.  263. 
Dibromide  of  Mercury,  ii.  300. 
Dichloride  of  Mercury,  ii.  298. 

Action  of  Ammo- 
nia on,  ii.  299. 
Dicyanide  of  Copper,  ii,  97. 
Didymium,  Arseniate  of,  ii.  277. 
Carbonate  of,  ii.  275. 
Chloride  of,  ii.  274. 
Estimation  of,  ii.  274. 
Metallic,  ii.  273. 
Nitrate  of,  ii.  276. 
Oxalate  of,  ii.  275. 
Peroxide  of,  ii.  274. 
Phosphate  of,  ii.  277. 
Protoxide  of,  ii.  273. 
Salts  of,  ii.  274. 
Sources  and  Extraction  of,  ii. 

73. 
Sulphate  of,  ii.  275. 
Sulphide  of,  ii.  274. 
Sulphite  of,  ii.  276. 
Diffusion-coefficients,  ii.  612. 
Diffusion  of  a  Salt  into  the  Solution   of 
another  Salt,  ii.  610. 
Gases,  i.  84. 

through  Porous  Septa, 
ii.  624. 
Liquids,  ii.  604. 


Diffusion    of   Liquids    through    Porous 

Septa,  ii.  616. 
Dilatation  of  Solids  by  Heat,  i.  3  ;  ii. 

421. 
Dimetaphosphoric  Acid,  ii.  693. 
Dimorphism,  i.  176. 
Diniodide  of  Copper,  ii.  97. 

Mercury,  ii.  300. 
Dioxide  of  copper,  ii.  95. 
Diplatosamine     and    Diplatinamine,    ii. 

382. 
Disinfecting  Properties  of  Charcoal,  ii. 

659. 
Dissipation  of  Heat,  i.  32, 
Distillation,  Natural  Sequel  to  Vaporisa- 
tion, i.  62. 
Disulphide  of  Copper,  ii.  96. 

Mercury,  ii.  298. 
Dolomite,  i.  592. 

Double  Decomposition  of  Salts,  i.  229;  ii. 

591, 

regarded     as    the 

Type  of  Chemical 

Action  in  general, 

ii.  519. 

Refraction,   Polarisation  by,   ii. 

459. 
Salts,  i.  197. 
Dutch  Liquid,  i.  386. 
Dynamical  Theory  of  Heat,  ii.  449. 


£. 


Earthenware  and  Porcelain,  I  613. 
Elasticity,  Axes  of,  in  Wood,  ii.  444. 
Electric  Current,  Heating  Power  of,  ii. 
506. 
reduced     to    absolute 
Mechanical      Mea- 
sure, ii.  506. 
Currents,  Measurement  of  the 

Force  of,  ii.  496. 
Resistance  of  Metals,  ii.  502. 
Electro  gilding,  ii.  359. 
Electrolysis,  i.  260. 
Electro-silvering,  ii.  360. 
Elementary  Bodies,  Atomic  Weights,  and 
Formula    of,  in   the    free 
State,  ii.  516. 
Substances,  Table  of,  i.  108 — 
110. 
Elements,  Arrangement  of,  in  Compounds, 
i.  184. 
Atomic   Volume  and   Specific 
Gravity     of,     Table    L,    i. 
211. 


786 


index; 


Elements,  Barium  Class  of,  i.  169. 
Carbon  Class  of,  i.  174. 
Chlorine  Class  of,  i.  171. 
Classification  of,  i.  168. 
Gold  Class  of,  i.  173. 
Magnesian  Class  of,  i.  168. 
Metallic,  i.  510. 
Non-metallic,  i.  291 ;  ii.  638. 
Phosphorus  Class  of,  i.  1 72. 
Platinum  Class  of,  i.  173. 
Potassium,  Class  of,  i.  170. 
Sulphur,  Class  of,  i.  168. 
Symbols  of  the,  i.  118. 
Tin,  Class  of,  i.  173. 
Tungsten,  Class  of,  i.  174. 
Emerald,  or  Beryl,  i.  617. 
Enamel,  i.  571. 

Endosmose  andExosmose,  ii.  616. 
Equivalent    of    Heat,    Mechanical,    ii. 
445. 
Values  of  Radicals,  ii.  524, 
Equivalents  and  Atoms,  ii.  509. 

Table  of,  i.  108-110. 
Erbia,  i.  618. 
Erbium,  i.  617. 

Etherification  explained  by  Atomic  Mo- 
tion, ii.  602. 
Ethers,  ii.  534. 

Action   of   Ammonia  on    Com- 
pound, ii.  557. 
Boiling  Points  of  Compound,  ii. 

584. 
Compound,  ii.  545. 

Sulphur,  ii.  548. 
Hydrosulphuric,  ii.  547. 
of  Bibasic  Acids,  ii.  539. 
Tribasic  Acids,  ii,  540. 
Ethylene,  ii.  564. 
Euchlorine  Gas,  i.  472. 
Euclase,  i.  617.      - 

Eudiometers    for    Measuring    Gases,    i. 
381. 
of  Bunsen,  i.  381. 
Evaporation  in  Vacuo,  i.  64. 

Spontaneous,  i.  90. 
Dalton    and   Regnault    on 
the,  of  Water,  i.  91. 
Expansion  and  the  Thermometer,  i,  2. 
of  Gases,  i.  12. 

Liquids,  i.  5,  7  ;  ii.  423. 
Mercury,  absolute,  ii.  425. 
Solids,  i.2;  ii.  221. 
Water,  ii.  424. 
Extinction   of   the   Chemical   Rays,   ii. 
495. 


F. 


Fahl-ores,  ii.  336. 

Faraday,  on  the  Liquefaction  of  Gases,  i. 
71. 
on  Relation  between  Light  and 
Magnetism,  i.  201  ;  ii.  481. 
Fatty  Acids,  ii.  538. 

Boiling  Points  of,  ii.  584. 
Felspar,  i.  612. 
Ferric  Acid,  ii.  53. 

Compounds,  ii.  43. 
Oxide,  ii.  43. 
Sulphide,  ii.  47. 
Ferrocyanide  of  Iron,  ii.  40. 

Potassium,  i.  29. 

and  Iron,  ii.  39. 
Ferroso-ferric  Oxide,  ii.  46. 

Sulphate,  ii.  51. 
Ferrous  Compounds,  ii.  36. 
Oxide,  ii.  36. 

Volumetric  estimation  of, 
ii.  728. 
Pick's  Experiments  on  Liquid  Diffusion, 

ii.  611. 
Flame,  Structure  of,  i.  381. 
Fluidity,  as  an  effect  of  Heat,  i.  41. 
Black's  Views  on,  i.  43. 
Table  of,  i.  42. 
Fluoboric  Acid,  i.  507. 
Fluoboride  of  Silicon,  i.  508. 
Fluorescence,  ii.  481. 
Fluoride  of  Aluminium,  i.  605. 
Boron,  i.  507. 
Calcium,  i.  586. 
Manganese,  ii.  8. 
Silver,  ii.  339. 
Tantalum,  ii.  284. 
Fluorides,  ii.  552. 
Fluorine,  i.  503. 

Detection  of  minute    quantities 

of,  ii.  720. 
Estimation  of,  ii.  721. 
Isolation  of,  ii.  720. 
Sources  of,  ii.  719. 
Fluor-Spar,  i.  505,  586. 
Fluosilicic  Acid,  i.  508. 
Formula?,  Rational,  ii.  521. 
Formulae,  Antithetic  or  Polar,  i.  204. 

of  Compounds,  i.  118. 
Freezing  Apparatus,  i.  586. 
of  Water,  i.  66. 
Mixtures,  i.  556. 
Fulminating  Gold,  ii.  351. 
Functions,    Classification  of  Bodies,  ac- 
cording to  their  Chemical,  ii.  528. 
Fusco-cobaltia  Salts,  ii.  69. 


INDEX. 


787 


Galvanometer,  i.  290  ;  ii.  497. 
Garnet,  i.  613.     • 
Gas-Battery,  Grove's,  i.  269. 
Gases  and  Vapours,  Specific  Heat  of,  ii. 
429. 
Air  and,  are  imperfect  Conductors, 

i.  31. 
Absorption  of,  by  Liquids,  i.  75, 

316;  ii.  647. 
Dalton  on  Miscibility  of,  i.  15. 
Density  of,  i.  79,  80. 
Determination     of     the    Specific 

Heat  of,  i.  25. 
Diffusion  of,  i.  86. 

through  Porous  Septa, 
ii.  624. 
Effusion  of,  i.  78. 
Expansion  of,  i.  12. 
Faraday's  Experiments  on,  i.  71. 
Heat  evolved  by  the  Solution  of,  in 

Water,  ii.  633. 
Passage  of,  through   Membranes, 

i.  89. 
Permanent,  i.  68. 
Priestley,  on  Diffusion  of,  i.  85. 
Table  of  the  Specific  Gravity  of, 

and  Vapours,  i.  149 — 155. 
Thilorier's  Machine  for  the  Lique- 
faction of  Carbonic  Acid,  i.  69. 
Transpiration  of,  i  82. 
Gerhardt's  Atomic  Weights,  ii.  513. 
Formulae  of  Salts,  i.  201. 
Theory  of   the    Ammoniacal 
Platinum  Compounds,  ii.  38 1 . 
Types,  ii.  523. 
Unitary  System,  ii.  512. 
German  Silver,  ii.  77. 
Gilding  and  Silvering,  ii.  359, 
Glass,  i.  568. 

Analysis  of,  i.  569. 
Bohemian,  i.  570. 

Composition  of.  Varieties  of,  i.  569. 
Crown,  i.  570. 
Crystal,  i.  571. 
Devitrification  of,    572. 
Flint,  i.  571. 
Green  or  Bottle,  i.  572. 
Window,  i.  569. 
Glauber's  Salts,  i.  555. 
Glucina  and  Ammonia,  Carbonate  of,  ii. 
ii.  763. 
Potash,  Oxalate  of,  ii.  763. 
Carbonate  of,  ii.  764. 
Glucina,  Estimation  and  Separation  of,  ii. 
765. 


Glucina,  Properties,    Rational    Formula 

and  Preparation  of,  ii.  762. 
Glucinum,  i.  615;  ii.  761. 
Gladstone's  Experiments  on  the  Influence 

of  Mass  on  Chemical  Action,  ii.  391. 
Glycerines,  ii.  533. 
Glycols,  ii.  532. 
Gold,  Alloys  of,  ii.  358. 
Amalgam  of,  ii.  358. 
and  Potassium,  Chloride  of,  ii.  356. 
Glass,  i.  173. 
Estimation   and   Separation   of,  ii. 

360. 
Extraction  of,  ii.  347. 
Oxide  of,  ii.  349. 
Fulminating,  ii.  351. 
Properties  of,  ii.  348. 
Sesquichloride  of,  ii.  355. 
Sesquioxide  of,  ii.  350. 
Sesquisulphide  of,  ii.  335. 
Sources  of,  ii.  346. 
Graham's  Experiments  on  Liquid  Diffu- 
sion, ii.  602. 
Researches  on  Osmose,  ii.  619. 
Graphite,  i.  358. 

Preparation    of    pure,    finely 
divided,  ii.  661. 
Graphitoidal  Boron,  ii.  668. 

Silicon,  ii.  672. 
Gunpowder,  i.  536. 
Gurney's  Bude  Light,  i.  384. 
Gypsum,  i.  589. 


H. 

Hail,  i.  330. 

Heat,  Absorption  and  Reflection  of  Radi- 
ated, i.  34. 

Bache's  Experiments  on  the  Radia- 
tion of,  i.  33. 

Capacity  of  Different  Bodies  for,  i. 
24. 

Central,  i.  40. 

Conduction  of,  i.  28  ;  ii.  441. 

Developed  by  Chemical  Combina- 
tion, ii.  625. 

Dilatation  of  Solids  by,  i.  3;  ii.  421. 

Distribution  of  the  Rays  of,  i.  106. 

Despretz  and  Dulong's  Experiments 
on  Latent,  i.  58. 

Dynamical  Theory  of,  ii.  449. 

Evolved  by  the  Solution  of  Gases 
in  Water,  ii.  632. 

Effects  of,  on  Glass,  i.  5. 

Evolved    in    the   Combination   of 
Acids  with  Water,  ii,  632. 

Experiments  of  Melloni  on  the 
Transmission  of,  i.  35  ; 
ii.  430. 


788 


INDEX. 


Heat,  Fluidity,  as  an  Effect  of,  i.  41. 
Latent,  i.  57  ;  ii.  430. 
Mechanical  Equivalent  of,  ii.  445. 
Nature  of,  i.  99,  101;  ii.  449. 
of  Combination  of  Acids  with  Bases, 
ii.  631,  632. 
Combinations    of    Metals    with 
Chlorine,  ii.  630. 
of  combination  of  Metals,  &c.  with 
Oxygen,  ii.  627. 
Combustion  and   Specific  Heat, 
Relations  between,  ii.  62. 
or  Cold  produced  by  Solution  of 

Salts  in  Water,  ii.  633. 
Radiation  of,  i.  31. 
Regnault's  Table  of  the   Capacity 

of  Bodies  for,  i.  25. 
Rumford's  Experiments  on  the  Ra- 
diation of,  i.  32. 
Specific,  i.  24  ;  ii.  426. 
Table  of  the   Conduction   of,  by 

Building  Materials,  i.  29. 
Transmission  of,  i.  35. 

Radiant,  through  Me- 
dia and  the  Effects 
of  Screens,  i.  34. 
Transparency  of  Bodies  to,  i.  36. 
Heating  Power  of  the  Voltaic  Current,  ii. 

.506. 
Hedyphar,  i.  590. 
Hemihedry,  ii.  476. 
Hexametaphosphoric  Acid,  ii.  694. 
Henry,  on  Coal  Gas,  i.  380. 
Hepar  Sulphuris,  i.  528. 
Homologous  Compounds,  Boiling  Points 

of,  ii.  585. 
Homologous  Series,  ii.  532. 
Horse-chestnut  Bark,    Fluorescence    of 

Infusion  of,  ii.  484. 
Humboldite,  i.  372. 
Hydracids,  i.  468. 

Hydrate  of  the  Binoxide  of  Calcium,  i. 
584. 
Potash,  Preparation  of,  from 
the  Nitrate,  ii.  731. 
Hydrated  Bisulphate  of  Potash,  i.  534. 

Sesquisulphate  of  Potash,  i.  534. 
Tantalic  Acid,  ii.  278. 
Hydrates  of  Alumina,  i.  602  ;  ii.  758. 
Copper,  ii.  96. 
Silicic  Acid,  i.  394. 
Sulphuric  Acid,  i.  409. 
the  Alcohol-radicals,  ii.  563. 
Aldehyde-radicals,  ii.  564. 
Metals  Proper,  ii.  563. 
Hydraulic  Mortar,  i.  584. 
Hydride  of  Phosphorus  (Liquid),  i.  453. 
Hydrides  of  Carbon,  i.  374. 
Hydriodic  Acid,  i.  497. 


Hydroboracite,  i.  600. 
Hydrobromic  Acid,  i.  489. 
Hydrochlorate  of  Ammonia,  ii.  736. 
Hydrochloric  Acid  and  Binoxide  of  Man- 
ganese, process  for 
preparing   Chlorine 
from,  ii.  454. 
Preparation  of,  i.  464. 
Table  of  the  Specific 

Gravity  of,  i.  467. 
Type,  ii.  523,  548. 
Hydrocyanic  Acid,  i.  531. 
Hydroferricyanic  Acid,  ii.  49. 
Hydroferrocyanic  Acid,  ii.  39.  ' 
Hydrofluoric  Acid,  i.  504,  505. 

Anhydrous,  ii.  720. 
Hydrofluosilicic  Acid,  i.  509. 
Hydrogen  and  Arsenic,  ii.  210. 

Nitrogen,  Ammonia,i.  353. 
Phosphorus,  i.  451. 
Sulphur,  i.  419. 
Antinioniuretted,  ii.  233. 
Bicarburetted,  i.  384. 
Binoxide  of,  i.  320, 
Bisulphide  of,  i.  423. 
Cavendish's   Experiments  on, 

i.  311. 
Peroxide  of,   i.  334. 
Preparation  of,  i.  305. 
Properties  of,  i.  307. 
Protocai'buretted,  i.  375. 
Protoxide  of,  i.  311. 
Quantitative  Estimation  of,  ii. 

645. 
Siliciurettcd,  ii.  676. 
Teroxide  of,  ii.  640. 
Hydrogen-type,  ii.  523,  563. 
Hydrosulphate  of  Ammonia,  ii.  737. 
Hydrosulphuric  Acid,  i.  419. 

Ethers,  ii.  547. 
Hygrometer,  i.  92. 

Condensing  (Regnault's),  i. 

96. 
Daniell's,  i.  95. 
Differential,  i.  93. 
Wet  Bulb,  i.  93. 
Hy perchloric  Acid,  i.  475. 
Hypochloric  Acid,  i.  478, 
Hypoclilorite  of  Lime,  i.  591. 
Hypochlorites,  i.  472. 

Volumetric  Estimation  of, 
ii.  725. 
Hypochlorous  Acid,  i.  469. 
Hypo-iodic  Acid.  ii.  712. 
Hypophosphorous  Acid,  i.  434. 

Analysis  of,  i.  437. 
Hyposulphate  of  Magnesia,  i.  599. 
Hyposulphate  of  Manganese,  ii.  10. 
Silver,  ii.  340. 


INDEX. 


'89 


Hyposulphite,  Cuprous,  ii.  98. 

of  Auric  Oxide  and  Soda, 
ii.  358. 
Aurous  Oxide  and  Soda, 

ii.  357. 
Baryta,  ii,  358. 
Silver,  ii.  340. 
Strontia,  i.  580. 
Hyposulphuric  Acid,  i.  413. 
Hyposulphurous  Acid,  i.  415. 

Estimation  of,  ii. 
687. 
Hydrotelluric  Acid,  ii.  200. 


I. 

Ilmenium,  ii.  290. 

Imides,  ii.  559. 

Inactive  Tartaric  Acid,  ii.  480. 

Induction,  Photo-chemical,  ii.  493 

Insolubility,   influence   of,   on  Chemical 

Decomposition,  i.  227  ;  ii.  601. 
Insoluble    Salts,    Decomposition    of,   by 

Soluble  Salts,  ii.  597. 
lodate  of  Potash,  i.  539. 
lodates,  i.  500. 
Iodic  Acid,  i.  498. 
Iodide,  Auric,  ii.  327. 
Cuprous,  ii.  97. 
Platinous,  ii.  368. 
of  Cadmium,  ii.  91. 
Lead,  ii.  119. 
Nitrogen,!.  501  j  ii.  713. 
Palladium,  ii.  386,  718. 
Potassium,  i.  529. 
Sulphur,  i.  502. 
Stannous,  ii.  135. 
Silver,  ii.  338. 

Tetramercurammonium,  ii.  3 1 7. 
Zinc,  ii.  85. 
Iodides,  ii.  496  ;  ii.  552. 

AtomicVolume  of  Liquid,  ii.  577. 
Ferric  and  Ferrous,  ii.  38,  48. 
of  Alcohol-radicals,  Action    of 
Ammonia  on,  ii.  554. 
Mercury,  ii.  300.  316. 
Phosphorus,  i.  502  ;  ii.  715. 
Iodine,  Bromides  of,  i.  503. 
Chlorides  of,  i.  502. 
Compounds  of,  i.  497. 
Estimation  of,  ii.  718. 
Preparation  of,  i.  491. 
Properties  of,  i.  494. 
Separation  of,  from  Bromine  and 

Chlorine,  ii.  719. 
Sources  of,  i.  491  ;  ii.  712. 
Uses  of,  i.  495. 

Volumetric  Estimation  of,  ii.  723. 
lodo-aurate  of  Potassium,  ii.  357. 


Ions,  Transference  of  the,  i.  265. 
Iridic  Sulphate,  ii.  397. 
Iridium,  Ammoniacal  Compounds  of,  ii. 
397. 
Carburet  of,  ii.  397. 
Chlorides  of,  ii.  396. 
Oxides  of,  ii.  394,  395. 
Properties  of,  ii.  393. 
Sources  and  Extraction  of,  ii. 

391. 
Sulphides  of,  ii.  395. 
Iron  and  Potassium,  Ferrocyanide  of,  ii.39. 
Bisulphide  of,  ii.  47. 
Black  or  Magnetic  Oxide  of,  ii.  46. 
Carbonate  of,  ii.  41. 
Cast,  ii.  28. 
Ferricyanide  of,  ii.  40. 
Malleable,  ii.  20. 
>  Metallurgy  of,  ii.  23. 
Ores  of,  ii.  24. 
Passive  condition  of,  ii.  35. 
Properties  of,  ii.  32. 
Protoacetate  of,  ii.  41. 
Protochloride  of,  ii.  38. 
Protocompounds  of,  ii.  36. 
Protocyanide  of,  ii.  38. 
Protiodide  of,  ii.  38. 
Protosulphate  of,  ii.  41. 
Protosulphide  of,  ii.  37. 
Protoxide  of,  ii.  36. 
Puddling  of,  ii.  30. 
Pyrites,  ii.  47. 

Quantitative  Estimation  of,  ii.  56. 
Scale  Oxide  of,  ii.  47. 
Separation  of,  from  other   Metals, 

ii.  57. 
Sf  squichloride  of,  ii.  48. 
Sesquicompounds  of,  ii.  43. 
Sesquicyanide  of,  ii.  48. 
Sesquiiodide  of,  ii.  48. 
Sesquioxide  or  Peroxide  of,  ii.  43. 
Sesquisulphide  of,  ii.  47. 
Sources  of,  ii.  23. 
Subsulphide  of,  ii.  39. 
Volumetric  Estimation  of,ii.  56,728. 
Isomerism,  i.  181. 
Isomorphism,  i.  159 — 167. 
Isomorphous  relations  of  Manganese,  ii.  2 1 . 


K. 


Kelp,  i.  562. 


Lanthanum,  Carbonate  of,  ii.  271. 
Chloride  of,  ii.  271. 
Estimation  of,  ii.  272. 
Metallic,  ii.  271. 


VOL.    II. 


3    H 


790 


INDEX. 


Lanthanum,  Nitrate  of,  ii.  272. 

Protoxide  of,  ii.  271. 
Sources  and  Extraction  of, 

ii.  268. 
Sulphate  of,  ii.  272. 
Latent  Heat,  i.  44  ;  ii.  430. 
Lead,  Acetates  of,  ii.  125. 

Alloys  of,  ii.  127. 

Antimoniates  of,  ii.  231. 

Bichloride  of,  ii.  118. 

Bioxide  or  Peroxide  of,  ii.  115 

Bromide,  Iodide,  and  Cyanide  of, 
ii.  119. 

Carbonate  of,  ii.  119. 

Chlorate  of,  ii.  124. 

Chloride  of,  ii.  117. 

Chlorite  of,  ii.  124. 

Chlorophosphate  of,  iL  125. 

Chromate  of,  ii.  169. 

Estimation  and  Separation  of,  ii.l28. 

Nitrate  of,  ii.  121. 

Nitrites  of,  ii.  122. 

Oxychloride  of,  ii.  1 1 7. 

Perchlorate  of,  ii.  124.        ^ 

Phosphate  of,  ii.  123. 

Protoxide  of,  ii.  112. 

Salts,  Reactions  of,  ii.  113. 

Sesquioxide  of,  ii.  115. 

Sources  and  Extraction  of,  ii.  HI. 

Suboxide  of,  ii.  112. 

Sulphate  of,  ii.  121. 

Sulphide  of,  ii.  116. 
Leslie,  Radiation  of  Heat,  i.  32. 
Leucite,  or  Amphigen,  i.  612. 
Liebig's  Condensing  Tube,  i.  63. 
Light,  Brewster  (Sir  D.)on,i.  105,  326. 

Change  of  Refrangibilityof,  ii.  481 . 

Common,  i.  103. 

Decomposition  of,  104. 

Difference  of  Chemical  Power  in 
Morning  and  Evening,  ii.  496. 

Double  Refraction  of,  i.  103  ;   ii. 
459. 

Forbes  on,  i.  326. 

Gurney's  Bude,  i.  384. 

Measurement  of  the  Chemical  Ac- 
tion of  ii.  489. 

Polarisation  of,  i.  103  ;  ii.  457. 

Faraday's  Experiments  on  the  Re- 
lations between  Magnetism  and, 
i.  281  ;  ii.  481. 
Lime,  i.  581. 

and  Alumina,  Silicates  of,  i.  613. 
Potash,  Sulphate  of,  ii.  751. 

Carbonate  of,  i.  587. 

Chromate  of,  ii.  167. 

Estimation  of,  ii.  751. 

Hydrate  of,  i.  582. 

Hypochlorite  of,  i.  591. 


Lime,  Hyposulphite  of,  i.  590. 
Nitrate  of,  i.  590. 
Phosphate  of,  i.  590  ;  ii.  751. 
Salts  of,  i.  587. 

Separation  of,  from    Baryta    and 
Strontia,  ii.  752. 
from  Magnesia  and 
the  Alkalies,   ii. 
752. 
Solubility  of,  ii.  750. 
Sulphate  of,  i.  589. 
Volumetric  Estimation  of  Chloride 
of,  i,  592 ;  ii.  726. 
Liquation  of  Argentiferous  Copper,  ii.  328, 
Liquefaction,  i.  41  ;  ii.  429. 
Liquids,  Absorption  of  Gases  by,  ii.  647. 
Atomic  Volume  of,  ii.  569. 
Circular  Polarisation  in,  ii.  468. 
Contraction  of,  from  the  boiling 

point,  i.  7  ;  ii.  424. 
Diffusion  of,  ii.  604. 

through  porous  Sep- 
ta, ii.  616. 
Expansion  of,  i.  57;  ii.  423. 
Latent  Heat  of,  ii.  431. 
Specific  Heat  of,  ii.  427. 
Tension  of  Vapours  of  mixed, 

ii.  439. 
Vaporisation  of,  i.  52. 
Lithia,  i.  573. 

Carbonate  of,  i.  574. 

Estimation  and  Separation  of,  ii. 

743. 
Hydrate  of,  i.  574. 
Nitrate  of,  ii.  743. 
Phosphate  of,  ii.  743. 
Sulphate  of,  i.  674. 
Lithium,  i.  573  ;  ii.  741. 

Chloride  of,  i.  574. 
Luteo-Cobaltia  Salts,  ii.  68. 


M. 


Madder-stove,  i.  98. 
Magnesia,  i.  594. 

Alba,  i.  596. 

Bicarbonate  of  Potash  and,  i. 
597. 

Borate  of,  i.  599. 

Carbonate  of,  i.  596. 

Chromate  of,  ii.  167. 

Estimation  and  Separation  of, 
ii.  755. 

Hyposulphate  of,  i.  599. 

Nitrate  of,  i.  599. 

Phosphate  of  and   Ammonia, 
i.  599. 

Silicates  of,  i.  600. 


INDEX. 


t9l 


Magnesia,  Sulphate  of,  i.  697. 
Magnesian  Class  of  Elements,  i.  168. 
Magnesium,  i.  594 ;  ii.  753. 

Chloride  of,  i.  595. 
Magnetic  Action,    Rotatory   Power  in- 
duced by,  ii.  481. 
and  Chemical  Actions  of  the 

Current  compared,  ii.  499. 
Oxide  of  Iron,  ii.  47. 
Magnetic  Polarity,  i.  235. 
Malaguti's  Experiments  on  the  Recipro- 
cal Action  of  Salts,  ii.  594. 
Malic  Acid,  Active  and  Inactive,  ii.  480. 
Malleability,  i.  511. 
Malleable  Iron,  ii.  29. 
Manganese,  Bioxide  or  Peroxide  of,  ii.  13. 
Carbonate  of,  ii.  8. 
Estimation  and    Separation 

of,  ii.  22. 
Fluoride  of,  ii.  8. 
Hyposulphate  of,  ii.  1 1. 
Isomorphous  relations  of,  ii. 

21. 
Molybdate  of,  ii.  191. 
Oxides  of,  ii.  3. 
Perchloride  of,  ii.  21. 
Phosphide  of,  ii.  6. 
Protochloride  of,  ii.  7. 
Protocyanide  of,  ii.  8. 
Protosulphide  of,  ii.  5. 
Protoxide,  ii.  3. 
Protosulphate  of,  ii.  8. 
Reactions  of,  ii.  4. 
Red  Oxide  of,  ii.  13 
Sources  and  Extraction   of, 

ii.  1. 
Sesquioxide  of,  ii.  10. 
Valuation  of  Bioxide  of,  ii.  14, 
Manganic  Acid,  ii.  18. 

Sulphate,  ii.  11. 
Manganous  Oxide,  ii.  3. 
Margueritte's  Experiments  on  the  Reci- 
procal Action  of  Salts,  ii.  594. 
Mariotte,  Deviation  from  the  Law  of,  in 
Gases,  i.  76. 
Law  of  Compression  of  Gases, 
i.  75. 
Marsh  Gas,  ii.  563. 
Marsh's  Test  for  Arsenic,  ii.  215. 
Mass,  Influence  of,  on  Chemical  Action, 

ii.  586. 
Measurement  of  the  Force  of  Electric 

Currents,  ii.  496. 
Mechanical  Equivalent  of  Heat,  ii.  445. 
Mechanical    Measure    of    the    Electric 

Current,  ii.  506. 
Mellon  (Liebig),  i.  388. 
Melting  Point  of  Sulphur,  i.  396  ;  ii.  681. 
Mercaptans,  ii.  546. 


Mercurammonia,  ii.  306. 
Mercurammonium,  Chloride  of,  ii  312. 
Mercuric  Amidochloride,  ii.  318. 
Ammonio-nitrates, 
Bromide,  ii.  315. 
Chloride,  ii.  308. 
Compounds,  ii.  303. 
Iodide,  ii.  315. 
Nitrates,  ii.  321. 
Oxide,  ii.  303. 

Seleniate  and  Selenite,  ii.  321. 
Sulphate,  ii.  320. 
Sulphide,  ii.  307. 
Sulphites,  ii.  321. 
Mercuroso-mercuric  Iodide,  ii.  318. 
Murcurous  Acetate,  ii.  303. 

Bromide,    or    Dibromide   of 

Mercury,  ii.  300. 
Carbonate,  or  Carbonate  of 
Black  Oxide  of  Mercury, 
ii.  301. 
Chloride,  DicLloride  of  Mer- 
cury, or  Calomel,  ii.  298. 
Compounds,  ii.  296. 
Iodide,  or  Diniodide  of  Mer- 
cury, ii.  300. 
Nitrates,  or  Nitrates  of  Black 
Oxide  of  Mercury,  ii.  302. 
ii.  301. 
Sulphates,     or    Sulphate    of 
Black  Oxide  of  Mercury, 
ii.  301, 
Seleniate,  ii.  301. 
Selenite,  ii.  301. 
Mercury,  Absolute  Expansion  of,  ii.  425. 
Action  of    Ammonia  on   Bi- 
chloride of,  ii.  299. 
Alloys  of,  and  Potassium,ii.324. 
Calorimeter,  ii.  626. 
Nitride  of,  ii.  306. 
Nitrochloride  of,  ii.  310. 
Chloride  of,    with   Ammonia, 

iL  309. 
Cyanide  of,  ii.  318. 
Dibromide  of,  ii.  300. 
Dichloride  of,  ii.  298.   ♦ 
Diniodide  of,  ii.  300. 
Disulphide  of,  ii.  298. 
Double  Salts  of  Chloride  of,  ii. 

313. 
Estimation  and  Separation  of, 

ii.  325. 
Oxy chloride  of,  i.  117  ;  ii.  312. 
Oxycyanide  of,  ii.  319. 
Protobromide  of,  ii,  315. 
Protochloride  of,  ii,  308. 
Protoxide  of,  ii.  303. 
Protosulphide  of,  ii.  307. 
Sulphochloride  of,  ii.  313. 


792 


INDEX. 


Metalloids  or  Acid  Metals,  ii.  567. 
Metals,  Alcohol-,  il  566. 

Combinations  of,  i.  514. 
Conduction  of  Heat  in,  ii.  440. 
Conjugate,  ii.  567. 
Diamagnetic,  i.  282. 
Electric  Resistance  of,  i.  502. 
Found  in  Native  Platinum,  i.  519; 

ii.  363. 
General  Observations  on,  i.  510 
Heat   of  Combination    of,   with 

Chlorine,  ii.  630. 
Heat   of  Combination   of,    with 

Oxygen,  ii.  627. 
Isomorphous    with   Phosphorus, 

i.  518;  ii.  203. 
in  Native  Platinum,  ii.  363. 
Mixed,  ii.  567. 
Noble,  ii.  291. 
of  the  Alkalies,  i.  517  ;  ii.  729. 

Alkaline  Earths,  i.  518;  ii. 

744. 
Earths  Proper,  i.  5 1 8 ;  7  63. 
Oxidability  of,  i.  513. 
Physical  Properties  of,  i.  511. 
Proper,  having  Isomorphous  Re- 
lations  with    the    Magnesian 
Family,  i.  518  ;  ii.  130. 
Proper,  having  Protoxides   iso- 
morphous  with  Magnesia,    i. 
518  ;  ii.  1. 
Proper,  Hydrides  of,  ii.  563. 
Proper,  of  which  the  Oxides  are 
reduced  by  Heat  to  the  Me- 
tallic state,  i.  519;  ii.  291. 
Protoxides  of,  i.  514. 
Table  of  the,  i.  510. 

Fusibility    of   dif- 
ferent, i.  512. 
Metameric  Bodies,  i.  183. 
Metaphosphates,  i.  442. 

Action  of  Water  on  the, 
ii.  694. 
Metaphosphoric  Acid,  i.  448  ;  ii.  692. 
Metastannates,  ii.  139. 
Metastannic  Acid,  ii.  138. 
Methylosulphurous  Acid,  ii.  706. 
Microcosmic  Salt,  i.  563. 
Minium,  ii.  115. 
Mitchell's  Experiments  on  Diffusion  of 

Gases,  i.  90. 
Mixed  Liquids,  Tension  of  Vapours  of, 
ii.  439. 
Metals,  ii.  567. 
Molybdate  of  Lead,  ii.  192. 

Manganese,  ii.  191. 
Molybdates  of  Ammonia,  ii.  190. 
Baryta,  ii.  191. 
Potash,  ii.  189. 


Molybdates  of  Soda,  ii.  190. 
Molybdenum,  Chlorides  of,  ii.  193. 

Estimation  and  Separation 
of,  ii.  193. 

Sources  of,  ii.  185. 

Sulphides  of,  ii.  192. 
Molybdic  Acid,  ii.  187. 

Oxide,  ii.  186. 
Molybdous  Oxide,  ii.  185. 
Monobasic  Salts,  i.  193. 
Monometaphosphoric  Acid,  ii.  693. 
Monophosphamide,  ii.  697. 
Monosul-hyposulphuric  Acid,  i.  417. 
Motion,  Atomic,  i.  660. 


N. 


Neutral    Metantimoniate   of   Potash,  ii. 

229. 
Nichol's  Prism,  ii.  460. 
Nickel,  Ammonio- Compounds  of,  ii.  77. 
Chloride  of,  ii.  76. 
Estimation  and  Separation  of,  ii. 

77. 
Oxides  of,  ii.  76. 
Sources  and  Extraction  of,  ii.  74. 
Sulphate  of,  ii.  76. 
Niobium,  ii.  285. 
Nitrate,  Cupric,  ii.  105. 
Ferric,  ii.  51. 
of  Alumina,  i.  610. 
Ammonium,  ii   738. 
Argentammonium,  ii.  342.    ' 
Baryta,  i.  578. 

Bimercurammonium,  ii.  323. 
Cobalt,  ii.  63. 
Didymium,  ii.  276. 
Lanthanum,  ii.  272. 
Lead,  ii.  121 
Lime,  i.  590. 
Lithia,  ii.  743. 
Magnesia,  i.  599. 
Palladium,  ii.  387. 
Potash,  i,  535. 
Silver,  ii.  341. 
Soda,  i.  562. 
Strontia,  i.  580. 
Tetramercurammonium,    ii. 

323. 
Trimercurammonium,  ii.  323. 
Uranyl,  ii.  257. 
Zinc,  ii.  86. 
Stannous,  ii.  135. 
Uranic,  ii.  257. 
Nitrates,  Mercuric,  ii.  322. 
Mercurous,  ii.  302. 
of  Bismuth,  ii.  247. 
Table  of,  i.  535. 


INDEX. 


793 


Nitre,  i.  535. 

valuation  of,  ii.  657. 
Nitric  Acid,  Action  of,  upon  Copper,  i. 
341. 
Anhydrous,  ii.  652. 
Battery  (Grove's),  i.  285. 
Estimation  of,  ii.  655. 
Preparation  of,  i.  346. 
Properties  of,  i,  341,  348. 
Uses,  i.  352. 
Nitric  Oxide,  Preparation  of,  ii.  652. 
Nitride  of  Boron,  ii.  670. 

Mercury,  ii.  306. 
Nitrides,  Intermediate,  ii.  561. 
Negative  or  Acid, 
of    the    Alcohol-radicals,    pri- 
mary, ii.  553. 
Alcohol-radicals,     se- 
condary and  tertiary, 
ii.  555. 
Aldehyde-radicals,  ii.  556. 
Titanium,  ii.  149. 
Positive,  ii.  553. 
Kitrile  Bases,  ii.  555.  ' 
Nitrite  of  Silver,  ii.  342. 
Nitrites  of  Lead,  ii.  122. 
Nitrochloride  of  Mercury,  ii.  310. 
Nitrogen,  i.  124. 

and  Hydrogen,    Ammonia,  i. 
353. 
Phosphorus,  i.  454. 
Sulphur,  i.  424. 
Binoxide  of,  i.  341. 
Bromide  of,  ii.  711. 
Chloride  of,  i.  480 ;  ii.  702. 
Chlorophosphide  of,  ii.  710. 
Compounds,  Atomic  Volume  of 

Liquid,  ii.  578. 
Compounds   containing  Phos- 
phorus and,  ii.  695. 
Iodide  of,  i.  501;  ii.  713. 
Peroxide  of,  i.  344. 
Preparation  of,  i.  322,  337  ;  ii. 

651. 
Properties  of,  i.  323. 
Protoxide  of,  i.  337. 
Quantitative  Estimation  of,  ii. 

653. 
Sulphide  of,  i.  424;  ii.  682. 
Nitrocyanide  of  Titanium,  ii.  150. 
Nitroprussic  Acid,  ii.  52. 
Nitroprussides,  ii.  55. 
Niti'osulphuric  Acid,  i.  411. 
Nitrous  Acid,  i.  343. 

Oxide,  ii.  652. 
Noble  Metals,  ii.  291. 
Non-metallic     Elements,     i.     291  ;     ii. 

638. 
Mormal  Acid  Fluid,  i.  550. 


Notation  and  Chemical  Nomenclature,  i. 
108-112. 
Classification,  Chemical,  ii. 
509. 


Octohedral  Boron,  ii.  668. 
Silicon,  ii.  673. 
Ohm's  Formulae,  ii.  500. 
Oil  Gas,  i.  386. 

of  Vitriol,  i.  405. 

Specific    Gravity    of   the 
Vapour  of,  i.  157. 
Olefiant  Gas,  or  Ethylene,  i.  384  ;     ii. 

564. 
Optical  and  Chemical  Extinction  of  the 

Chemical  Rays,  ii.  495. 
Organic  Compounds,  Circular  Polarisation 
in,  ii.  468. 
Estimation  of  Carbon 
and  Hydrogen  in, 
ii.  662. 
Estimation  of  Chlo- 
rine in,  ii.  717. 
Estimation  of  Nitro- 
gen in,  ii.  652. 
Estimation    of    Sul- 
phur in,  ii.  687. 
Osmiamic  Acid,  ii.  404. 
Osmic  Acid,  ii.  403. 

Sulphate,  ii.  401. 
Osmious  Acid,  ii.  402. 
Osmium,  Bichloride  of,  ii.  401. 

Estimation  and  Separation  of, 

ii.  405. 
Oxides  and  Chlorides  of,  ii.  400. 
Sources  and  Extraction  of,  ii. 

399. 
Sesquioxide  of,  ii.  400. 
Sulphides  of,  ii.  405. 
Terchloride  of  ii.  403. 
Osmose  through  Membrane,  ii.  620. 

Physiological  Action  of,  ii.  623. 
through    Porous    Earthenware, 

ii.  619. 
Jolly's  researches  on,  ii.  617. 
Graham's  researches  on,  ii.  619. 
Oxalate,  Cerous,  ii.  265. 
Ferric,  ii.  53. 

of  Chromium  and  Potassium,  ii. 
161. 
Copper  and  Potash,  ii.  105. 
Didymium,  ii.  275. 
Glucina  and  Potash,  ii.  763. 
Potash  and  Antimony,  ii.  226. 
Silver,  ii.  343. 
Oxalates,  Decomposition  of  Insoluble  by 
Alkaline  Carbonates,  ii.  599. 


3  H  3 


794 


INDEX. 


Oxalates  of  Ammonium,  ii.  740. 
Oxamide,  ii.  558,  740, 
Oxalic  Acid,  i.  372. 

Estimation  of,  ii.  665. 
Oxamic  Acid,  ii.  542,  740. 
Oxide,  Antimonic,  ii.  222. 
Auric,  ii.  350. 
Aurous,  ii.  349. 
Ceric,  ii.  264. 
Cerous,  ii.  263. 
Chromic,  ii.  155. 
Chromoso-chromic,  ii.  155. 
Chromous,  ii,  153. 
Cobaltic,  ii.  65. 
Cobaltous,  ii.  61. 
Cupric,  ii.  99. 
Cuprous,  ii.  95. 
Mercuric,  ii.  303. 
Molybdic,  ii.  186. 
Molybdous,  ii.  185. 
of  Antimony,  ii.  222. 
Cadmium,  ii,  30. 
Gold,  ii   349. 
Iridium,  ii,  394,  395. 
Iron,    Volumetric    Estimation 

of,  ii.  728. 
Manganese,  ii.  3,  10,  13. 
Rhodium,  ii,  407. 
Silver,  ii,  333, 
Phosphorus,  i.  633. 
Potassium,  Salts  of,  i.  532, 
Vanadium,  ii.  174. 
Zinc,  ii.  84. 
Palladous,  ii.  385. 
Platinic,  ii.  368. 
Platinous,  ii,  367. 
Rhodic,  ii,  407. 
Ruthenic,  ii.  415. 
Stannic,  ii.  136. 
Stannous,  ii.  131. 
Tungstic,  ii.  177- 
Uranic,  ii.  255. 
Uranosouranic,  ii.  254. 
Uranous,  ii,  253. 
Oxides  and  Chlorides  of  Osmium,  ii.  400. 
Atomic     Volume     and     Specific 

Gravity  of,  i.  215,  216. 
Intermediate,   or   Oxygen   Salts, 

ii.  544, 
Metallic,  Classification  of,  ii.  530. 
Negative  or  Acid,  ii.  535. 
Positive,  ii.  530, 
Oxy chloric  Acid,  i.  475. 
Oxy bromide  of  Phosphorus,  ii.  711. 
Oxychloride  of  Lead,  ii,  1 1 7. 

Mercury,  ii.  312. 
Oxycobaltia-salts,  ii,  68, 
Oxy  cyanide  of  Mercury,  ii.  319. 
Oxygen,  i.  123. 


Oxygen -Acids,  i.  186. 

Active  Modification  of,  ii.  641, 

644. 
Compounds   of   Chlorine    and, 

i,  469. 
Extraction  of,  from  Atmosphe- 
ric Air,  ii,  638. 
Heat  produced  by  combination 

-with,  ii.  627. 
Preparation  of,  i.  291. 
Properties  of,  i,  296. 
Quantitative  Estimation  of,   ii. 
645. 
Oxygenated  Water,  i.  185, 
Oxygen-Salts  or  Intermediate  Oxides,  ii. 

644. 
Ozone,  i.  304  ;  ii.  639. 


Packfong,  ii,  77. 

Palladium,  Ammoniacal  Compounds  of, 
ii,  388-390. 
Chlorides  of,  ii,  387,  388. 
Cyanide  of,  ii.  387. 
Estimation    and     Separation 

of,  ii.  391. 
Nitrate  of,  ii.  387. 
Properties  of,  ii,  385. 
Protoxide  of,  ii.  385. 
Reactions  of,  ii.  386. 
Sources  and  Extraction  of,  ii. 

384. 
Sulphide  of,  ii.  386. 
Passive  condition  of  Iron,  ii.  35. 
Pearl- Ash,  i.  533. 

Pentachloride  of  Antimony,  ii,  232. 
Phosphorus,  i.  487. 

Action     of 
Acids  on, 
ii.  708. 
Pentaiodic  Acid,  i.  501. 
Pentasulphide  of  Antimony,  ii.  232. 
Pentathioaic  Acid,  i.  418. 
Perchlorate  of  Lead,  ii,  1 24, 

Potash,  i.  539. 
Perchloric  Acid,  i,  475.^ 
Perchloride  of  Carbon,  i.  483. 

Sulphite  of,  ii,  751 
Manganese,  ii,  21. 
Periodates,  i,  501. 
Periodic  Acid,  i.  501. 
Permanganic  Acid,  ii.  18. 
Permeability   to    Liquids,   Axes   of,    in 

Wood,  ii.  444. 
Persulphide  of  Arsenic,  ii.  209 
Peroxide  of  Chlorine,  i,  478. 

Didymium,  ii,  274. 

Iron,  ii.  43.  x 


INDEX. 


795 


Peroxide  of  Lead,  ii.  116. 

Manganese,  ii.  13. 
Nitrogen,  i.  344. 
Potassium,  i.  527. 
Silver,  ii.  343. 
Peroxides,    Volumetric  Estimation  of,  ii. 

727. 
Phospham,  ii.  698. 
Pliosphamic  Acid,  ii.  697. 
Phosphate,  Cerous,  ii.  266. 

of  Alumina,  i.  610. 
Cobalt,  ii.  65. 
Didymium,  ii.  279. 
Lead,  ii.  123. 
Lime,  i.  590;  ii.  751. 
Lithia,  ii.  743. 
Magnesia,  i.  599. 

and     Ammonia, 
i.  599. 
Phosphates,  i.  43. 

Analysis  of,  i.  449 ;  ii.  700. 
Bibasic,  i.  444. 

of     Ammonium,    ii. 
739. 
of  Uranyl,  ii.  257. 

Zinc,  ii.  86. 
Tribasic,  i.  444. 
Uranic,  ii.  257. 
Phosphide  of  Cobalt,  ii.  67- 

Manganese,  ii.  6. 
Nitrogen,  i.  454;  ii.  699. 
Tungsten,  ii.  182. 
Phosphides,  ii.  562. 
Phosphites,  i.  437. 
Phosphocerite,  ii.  266. 
Phosphoric  Acid,  Analysis  of,  i.  449. 

Action  of,  onPentachlo- 
ride  of  Phosphorus, 
ii.  710. 
Amides  of,  ii.  695. 
considered  Tribasic,   i. 

208. 
Deuto-hydrate  of.  Acid 
or  Bibasic  Phosphate 
of  Water,  i.  441. 
Estimation  of,  ii.  700. 
Separation      of,     from 

Bases,  ii.  701. 
Preparation  of,  i.  438. 
Protohydrate  of,  i.  442. 
Terhydrate  of,  or  Tri- 
basic   Phosphate    of 
Water,  i.  440. 
Phosphorous  Acid,  Analysis  of,  i.  437. 

Estimation  of,  ii.  702. 
Preparation  of,  i.  436. 
Properties  of,  i.  437. 
Phosphorus,  i.  429. 

Atomic  Weight  of,  ii.  692. 


Phosphorus  and  Hydrogen,  i.  451. 

Nitrogen,  i.  454;  ii.  695. 
Sulphur,  i.  454. 
Bromide  of,  i.  491. 
Chloride  of,  i.  487. 
Chlorosulphide  of,  i.  487. 
Chloroxide  of,  i.  487. 
Class  of  Elements,  i.  172. 
Estimation  of,  ii.  701. 
Iodides  of,  i.  502;  ii.  715. 
Liquid  Hydride  of,  i.  453. 
Oxide  of,  i.  433. 
Oxy bromide  of,  ii.  711- 
Pentachloride  of,  i.  487. 
Properties  of,  i.  431. 
Red  or  Amorphous,  ii.  690. 
Solid  Hydride  of,  i.  451. 
Sulphides  of,  i.  454  ;  ii.  695. 
Sulphobromide  of,  ii.  711. 
Terchloride  of,  i.  487. 
Phosphoryl,  Chloride  of,  ii.  551. 
Phosphuretted  Hydrogen  Gas,  i.  151. 
Photo-Chemical  Induction,  ii.  493. 
Platinic  Chloride,  ii.  369. 

Oxide,  ii.  368. 
Platinised  Charcoal,  ii.  660. 
Platinocyanides,  ii.  367. 
Platinous  Chloride,  ii.  367. 
Cyanide,  ii.  308. 
Iodide,  ii.  368. 
Oxide,  ii.  367. 
Platammonium,  Bisalts  of,  ii.  376,  378. 

Proto-saltsofjii.  372-374. 
Platinum  Black,  ii.  365. 

Bichloride  of,  ii.  339. 
Bioxide  of,  ii.  368. 
Bisulphide  of,  ii.  36 
Class  of  Elements,  ii.  173. 
Estimation  and  Separation  of, 

ii.  383. 
Extraction  of,  ii.  363. 
Inflammation  of  Mixed  Oxy- 
gen and  Hydrogen  by,  i.  269. 
Metals  in  Native,  ii.  363. 
Process   of  rendering    malle- 
able, ii.  365. 
Protochloride  of,  ii.  367, 
Protosulphide  of,  ii.  367. 
Protoxide  of,  ii.  367. 
Residues,  New  Method  of  treat- 
ing, ii.  417. 
Salts,  Ammoniacal,  ii.  371-382. 
Sources  of,  ii.  363. 
Spongy,  ii.  364. 
Sulphocyanides  of,  ii.  371. 
Platosamine  and  Platinamine,  ii.  382. 
Polar  Chains,  i.  275. 

Formulae,  i.  204. 

Liquids,  Separation  of,  i.  263. 


3  H  4 


796 


INDEX. 


Polarisation,  Circular,  ii.  464. 

of  Light,  i.  103,  281 ;  ii.  457. 
Polarised  Light,  Nature  of,  ii.  461. 
Polarisation  hy  Reflection,  ii.  457. 

Refraction,    Single   and 
Double,  ii.  459. 
Tourmalines,  ii.  461. 
Polarity,  Chemical,  i.  235. 

Illustrations  from  Magnetical,  i. 

235. 
of  Arrangement,  i.  243. 
Polybasite,  ii.  336. 
Polythionic  Series,  i.  417. 
Porcelain  and  Earthenware,  i.  613. 
Potash,  i.  524. 

Acid  Antimoniate  of,  ii.  229. 

Metantimoniate  of,  ii.  229. 
Action  of  Chlorine  upon,  i.  473. 
Antimoniates  of,  ii.  229. 
and  Antimony,  Oxalate  of,  ii.  226. 
Tartrate  of,  ii.  226. 
Glucina,  Oxalate  of,  ii.  763. 
Lime,  Sulphate  of,  ii.  751. 
Soda,  Carbonate  of,  i.  554. 
Sulphate  of,  ii.  735. 
Aurate  of,  ii.  352. 
Aurosulphite  of,  ii.  852. 
Bicarbonate  of,  i.  533. 
Bichromate  of,  ii.  165. 
Bihydrosulphate  of,  i.  528. 
Chlorate  of,  i.  537. 
Chromate  of,  ii.  165. 
Estimation  of  ii.  731. 
Felspar,  i.  612. 
Hydrate  of,  i.  524.  ii.  731. 
Hydrated  Bisulphate  of,  i.  534. 
Sesquisulphate    of,    i. 
534. 
Hydriodate  of,  i.  529. 
lodate  of,  i.  539. 
Ley,  i.  525. 
Mulybdates  of,  ii.  189. 
Neutral    Metantimoniate  of,    ii. 

229. 
Nitrate  of,  i.  535. 
Valuation  of,  ii.  657. 
Perchlorate  of,  i.  538. 
Preparation  of  Hydrate  of,  from 

the  Nitrate,ii.  731. 
Red  Prussiate  of,  i.  530. 
Sulphate  of,  i.  534. 
Tellurate  of,  ii.  199. 
Terchromate  of,  ii.  166. 
Yellow  Prussiate  of,  i.  529. 
Potassio-ferrous  Tartrate,  ii.  43. 
Potashes,  i.  533. 
Potassa,  i.  524. 
Potassium,  Chloride  of,  i.  528. 

and  Gold,  Chloride  of,  356. 


I    Potassium   and   Iron,   Ferrocyanide    of, 
ii.  39. 
Mercury,    Cyanide     of, 

ii.  320. 
Rhodium,   Chloride    of, 
ii.  410. 
Chloroplatinate  of,  ii.  370. 
Chloroplatinite  of,  ii.  368. 
Class  of  Elements,  i.  170. 
Compounds  of,  i.  524. 
Cyanide  of,  i.  530. 
Estimation  of,  ii.  731. 
Ferricyanide  of,  i.  530. 
Ferrocyanide  of,  i.  529. 
Improvements  in  the  Prepa- 
paration    of,    by    Maresca 
and  Donny,  ii.  729. 
Iodide  of,  i.  528. 
lodo-aurate  of,  ii.  357. 
Pentasulphide  of,  i.  528. 
Peroxide  of,  i.  527. 
Preparation  of,  i.  519. 

by     Electro- 
lysis, ii.  729. 
Properties  of,  i.  523. 
Protosulphide  of,  i.  527. 
Salts  of  Oxide  of,  i.  532. 
Separation  of,  from   Sodium, 

ii.  735. 
Sulphides  of,  i.  527. 
Sulphocyauide  of,  i.  532. 
Telluride  of,  ii.  201. 
Trisulphide  of,  i.  528. 
Priestley  on  Diflfusion  of  Gases,  i.  85. 
Prism,  Nichol's,  ii.  460. 
Proto-acetate  of  Iron,  ii.  43. 
Protobromide  of  Mercury,  ii.  315. 
Protocarburetted  Hydrogen  :  —  Experi- 
ments on,  i.  380. 

Preparation  and,  i  375. 
Properties  of,  i.  375,  376. 
Protochloride  of  Carbon,  i.  483. 

Sulphite  of,  ii. 
704. 
Cerium,  ii.  265. 
Chromium,  ii.  154. 
Copper,  ii.  101. 
Iridium,  ii.  396. 
Iron,  ii.  38. 
Mercury,  ii.  308. 
Platinum,  ii.  367, 
Rhodium,  ii.  409. 
Ruthenium,  ii.  414. 
Sulphur,  i.  486. 
Tin,  ii.  133. 
Tin  and  Potassium,  ii. 

135. 
Uranium,  ii.  254. 
Protocyanide  of  Iron,  ii.  38. 


INDEX. 


797 


Protofluoride  of  Cerium,  ii.  268. 
Proto- hydrate  of  Phosphoric  Acid,  i.  442. 
Protiodide  of  Mercury,  ii.  315. 
Protosulphurets  i.  410. 
Protoxide  of  Cerium,  ii.  263. 

Chromium,  ii.  153. 

Cobalt,  ii.  61. 

Copper,  ii.  99. 

Didymium,  ii.  273. 

Iridium,  ii.  394. 

Iron,  ii.  36. 

Lanthanum,  ii.  271. 

Lead,  ii.  112. 

Mercury,  ii.  303. 

Nickel,  ii.  76. 

Nitrogen,  i.  337. 

Palladium,  ii.  385. 

Platinum,  ii.  367. 

Ruthenium,  ii.  413. 

Tin,  ii.  131. 

Titanium,  ii.  146. 

Silver,  ii.  333. 

Uranium,  ii.  253. 

Vanadium,  ii.  173. 
Protoxides  of  Metals,  i.  514;  ii.  514,  530. 
Protosalts  of  Ammo-platammonium,   ii. 
375,  376. 
Platammonium,  ii.  372 — 374. 
Protosulphate  of  Iron,  ii.  41. 
Protosulphide  of  Carbon,  ii.  684, 
Cerium,  ii.  264. 
Iron,  ii.  37. 
Mercury,  ii.  307. 
Platinum,  ii.  367. 
Tin,  ii.  133. 
Prussian  Blue,  ii.  49. 
Prussine,  i.  200. 
Psychrometer,  i.  93.  94. 
Purple  of  Cassius,  ii.  353. 
Pyrites  Iron.  ii.  47. 
Pyrometer,  Daniell's  and  Wedgwood's,  i. 

19,  20. 
Pyrophosphamic  Acid,  ii.  700. 
Pyrophosphate  of  Soda.  i.  444. 
Pyrophosphoric  Acid,  i.  442. 


Quadroxide  of  Bismuth,  ii.  243. 
Quartation  of  Gold  and  Silver,  ii.  347. 
Quartz,  Left  and  Right-handed,  ii.  465. 
Quinine,  Fluorescence  of  Salts  of,  ii.  482. 


R. 


Racemic  Acid,  Composition  of,  ii.  479. 
Radiant  Heat,  i.  34. 
Radicals  and  Types,  ii.  521. 


Radicals  Conjugate,  ii.  526. 

Equivalent  Values  of,  ii.  524. 
Rain,  Mean  Fall  of,  in  London,  i.  330. 
in  Northern  Europe,  Central   Eu- 
rope, and  in   South   Europe,  L 
330. 
in  York,  i.  330. 
Rational  Formula  and  Atomic  Volume, 
Relation  between,  ii.  580. 
Formulae,  ii.  521. 
Rays,  Chemical,  i.  107. 

Deoxidising,  i.  107. 
Reaumur,  Thermometer  of,  i.  18. 
Reciprocal  Action  of  Salts,  ii.  544. 
Red  Lead,  ii.  115. 

Oxide  of  Copper,  ii.  d5. 
Phosphorus,  ii.  690. 
Sulphur,  ii.  681. 
Reduction  of  the  Force  of  the  Electric 
Current  to  absolute  Mecha- 
nical Measure,  ii.  517. 
Test  for  Arsenic,  ii.  2 1 3. 
Reflection,  Polarisation  by,  ii.  457. 
Refraction,  Polarisation  by,  ii.  459. 
Refrangibility  of  Light,    Change  of,  ii. 

481. 
Regnault,  Condenser-Hygrometer,  i.  96. 
Experiments  on  Gases,  i.  77. 

Oxygen,  i.  296. 
on  Atomic  Heat,  i.  1 39. 

Evaporation  of  Water,  i.  9 1 . 
the  Weight  of  Air,  i.  324. 
Table  of  Specific  Heat,  i.  25. 
the  Specific  Heat  of 
Compounds  i.  141, 
142. 
Gases,  ii.  429. 
Tension  of  Vapour  of  Water  in 
Vacuo,  i.  65;  ii.435. 
Resistance  of  Metals,  Electric,  ii.  502. 
Respirators,  Charcoal,  ii.  658. 
Rheometers,  ii.  497. 
Rheostat,  ii.  504. 
Rhodic  Acid,  ii.407. 
Rhodium  and  .Potassium,  Chloride  of,  ii. 
410. 
Estimation  and  Separation  of, 

ii  411. 
Oxides  of,  ii.  407. 
Protochloride  of,  ii.  409. 
Sesquichloride  of,  ii.  409. 
Sources  and  Extraction  of,  ii. 

406. 
Sulphate  of,  ii.  410. 
Sulphide  of,  ii.  409. 
Rose's  Fusible  Metal,  i.  11, 
Roseocobaltia  Salts,  ii.  70. 
Rotatory  Power  and  Crystalline  Form, 
Relations  between,  ii.  476. 


798 


INDKX. 


Rotatory  Power  induced   by   Magnetic 
Action,  i.  281 ;  ii.  481. 
Power,  Specific,  ii.  469. 
Ruthenic  Acid,  ii.  416. 
Oxide,  ii.  415. 
Sulphate,  ii.  416. 
Ruthenium,  Bioxide  of,  ii.  415. 

Bichloride  of,  ii.  416. 
Estimation  and  Separation  of, 

ii.  417. 
Protochloride  of,  ii.  414. 
Protoxide  of,  ii.  413. 
Sesquichloride  of,  ii.  41 5. 
Sources  and  Extraction   of, 

ii.  412. 
Sesquioxide  of,  ii.  414. 
Sulphides  of,  ii.  417. 
Rutherford's  Thermometer,  i.  27. 


Saccharimetry,  ii.  469. 
Saccharine  Solutions,  Table  for  the  Ana- 
lysis of,  ii.  475. 
Safety  Lamp,  Davy's,  i.  377. 
Sal- alembroth,  ii.  314. 
Saline  Solutions,  Tension  of  Vapours  of, 
ii.  437. 
Waters,  i.  319. 
Sal-prunelle,  i.  535. 
Salt,  Microcosmic,  i.  563. 
Saltpetre,  i.  535. 

Valuation  of,  ii.  657. 
Salts  of  Cobalt,  Ammoniacal,  ii.  68. 

Tin,  ii.  133. 
Salts,  i.  130. 

Acid,  Neutral,  and  Basic,  ii.  544. 
Amidogen,  or  Intermediate  Nitrides, 

ii.  561. 
Analysis  of  (Wenzel),  i.  131. 
Atomic  Volume  and  Specific  Gra- 
vity of,  Table  IL,  i.  213. 
Bibasic,  i.  193. 
Calorific  Effect  of  Solution  of,  in 

Water,  ii.  633. 
Constitution  of,  L  186 — 201. 
Decomposition  of  Ammoniacal,  i. 
205. 
,  Insoluble,      by 
Soluble,      ii. 
597. 
by      Diffusion, 
ii.  613. 
Derivations  of  Double  by  Substitu- 
tion, i.  199. 
Diffusion  of,  ii.  606. 
Double,  i.  197. 


Salts,  Double  Decomposition  of,  i.  229 — 
233. 
Formation   of,   by  Substitution,   i. 

201. 
Glauber's,  i.  555. 
Heat  produced  in  the  Formation  of, 

ii.  631. 
Monobasic,  i.  193. 

the  Type  of  Red  Chro- 

mateof  Potash,  i.  196. 

Oxygen,  or   Intermediate   Oxides, 

ii.  544. 
Reciprocal  Action  of,  ii.  591 — 604. 
Solubility  of,  in  100  parts  of  Water, 

i.  220. 
Solution  of,  i.  219. 
Sulphur,  ii.  548. 
Table  of,  i.  141. 
Tribasic,  i.  194. 

usually  denominated   Subsalts,    i. 
194. 
Scale-oxide  of  Iron,  ii.  47, 
Scales  of  Chemical  Equivalents,  i.  131. 
Schweitzer,  Analysis  of  Sea- water,  i.  319. 
Sea- salt,  i,  642. 
Sea- water.  Analysis  of,  i.  319. 
Secondary  Decomposition,  i.  262. 
Seleniate  and  Selenite,  Mercuric,  ii.  327. 
Mercurous,  ii.  301. 
of  Baryta,  Decomposition  of,  by 
Alkaline  Carbonates,  ii.  599. 
Selenic  Acid,  i.  429. 
Selenide  of  Bismuth,  ii.  244. 
Selenides,  ii.  546. 
Selenious  Acid,  i.  428. 
Selenium,  Allotropic  Modifications  of,  ii. 
688. 
Estimation  of,  ii.  689. 
Preparation  of,  ii.  688. 
Properties  of,  i.  427. 
Sesquicarbonate  of  Soda,  i.  553. 
Sesquichloride  of  Carbon,  i.  481. 
Cerium,  ii.  265. 
Chromium,  ii.  139. 
Gold,  ii.  355. 
Iridium,  ii.  396. 
Iron,  ii.  48. 
Ruthenium,  ii.  415. 
Sesquicom pounds  of  Iron,  ii.  43. 
Sesquicyanide  of  Cobalt,  ii.  67. 

Iron,  ii.  48. 
Sesquioxide  of  Cerium,  ii.  263. 

Chromium,  ii.  155. 
Cobalt,  ii.  65. 
Gold,  ii.  350. 
Iron,  ii.  43. 
Lead,  ii.  115. 
Manganese,  ii.  10. 
Nickel,  ii.  76. 


INDEX. 


799 


Sesquioxide  of  Osmium,  ii.  400. 

Ruthenium,  ii.  414. 
Titanium,  ii.  147. 
Tin,  ii.  136. 
Uranium,  ii.  255. 
Sesquisulphide  of  Chromium,  ii.  159. 
Iron,  ii.  47. 
Gold,  ii.  355. 
Silica  or  Silicic  Acid:  — 

Dissolved  by  Acids,  i.  393. 
Hydrates  of,  i.  394;  ii.  675. 
Preparation  and  Properties  of,  i. 
393. 
Silicate  of  Soda  and  Lime,  i.  569. 

Zinc,  ii.  87. 
Silicates,  i.  395. 

Analysis  of,  ii.  677. 
of  Alumina,  i.  572,  610. 

Lime    and    of    Alumina,    i. 

613. 
Magnesia,  i.  600. 
Potash  and  Lead,  i.  571. 
Soda,  i.  567. 
Silicic  Acid  dissolved  by  Acids,  i.  393. 
Estimation  of,  ii.  677. 
Formula  of,  ii.  674. 
Hydrates  of,  ii.  675. 
Siliciuretted  Hydrogen,  ii.  676. 
Silicon  or  Silicium,  AUotropic  Modifica- 
tions of,  ii.  672. 
Atomic  Weight  of,  ii.  674. 
Estimation  of,  ii.  677. 
Silicon   and   Hydrogen,    Chloride,   Bro- 
mide, and  Iodide  of,  ii.  765. 
Silicon,  Hydrated  Oxide  of,  ii.  765. 
Chloride  of,  i.  484. 
Bromide  of,  i.  491. 
Preparation  of,  i.  391 ; 

ii.  672. 
Properties  of,  i.  392. 
Silver,  Alloys  of,  ii.  343. 

Ammonio-nitrate  of,  ii.  212. 
Assay  of,  ii.  345. 
Bromide  of,  ii.  338. 
Carbonate  of,  ii.  339. 
Chromate  of,  ii.  169. 
Cupellation  of,  ii.  346. 
Cyanide  of,  ii.  339. 
Estimation  and  Separation  of,  ii. 

344. 
Fluoride  of,  ii.  339. 
Hyposulphate  of,  ii.  340. 
Hyposulphite  of,  ii.  340. 
Iodide  of,  ii.  338. 
Metallurgy  of,  ii.  328. 
Nitrate  of,  ii.  341. 
Nitrite  of,  ii.  342. 
Oxalate  of,  ii.  343. 
Peroxide  of,  ii.  343. 


Silver,  Properties  of,  ii.  331. 
Protoxide  of,  ii.  333. 
Sources  of,  ii.  328. 
Suboxide  of,  ii.  332. 
Sulphate  of,  ii.  339. 
Sulphide  of,  ii.  336. 
Silvering,  ii.  359. 
Silver-ores,  Treatment  of,  ii.  328. 
Silver-salts,  Reactions  of,  ii.  334. 
Simmler  and  Wilde's  Researches  on  Li- 
quid Diffusion,  ii.  613. 
Six's  Thermometer,  i.  22. 
Soda,  i.  526,  540. 

and  Auric  Oxide,  Hyposulphite  of, 
ii.  358. 
Aurous  Oxide,    Hyposulphite 

of,  ii.  357. 
Potash,  Carbonate  of,  i.  554. 
Sulphate  of,  ii.  735. 
Ash,  i.  546. 
Alum,  i.  609. 

Biborate  of  (Borax),  i.  565. 
Bicarbonate  of,  i.  582. 
Biphosphate,  i.  563. 
Bipyrophosphate  of,  i.  564. 
Bisulphate  of,  i.  562. 
Carbonate  of,  i.  544. 
Chlorate  of,  i.  562. 
Chromate  of,  ii.  166. 
Furnace,  i.  558. 

Hydrates  of  Carbonate  of,  ii.  733. 
Hyposulphite  of,  i.  550. 
Metaphosphate  of,  i.  444,  564. 
Molybdates  of,  ii.  190. 
Nitrate  of,  i.  562. 
Phosphates  of,  i.  562—563. 
Preparation  of  Carbonate  of,  from 

the  Sulphate,  i.  557. 
Preparation  of  Sulphate  of,  i.  558. 
Pyrophosphate  of,  i.  444,  564, 
Salt,  i.  546. 

Sesquicarbonate  of,  i.  553. 
Silicates  of,  i.  567. 
Solubility  of  Carbonate  of,  ii.  733. 
Sulphate  of,  ii.  735. 
Solution  of  Caustic,  i.  541. 
Sub  phosphate  of,  i.  563. 
Sulphate  of,  i.  665. 
Sulphite  of,  i.  554. 
Sodium,  i.  540. 

Chloride  of,  i.  542. 
Chloroplatinate  of,  ii.  370. 
Compounds  of,  i.  540. 
Estimation    and  Separation    of, 

ii.  735. 
Preparation  of,  i.  540 ;  ii.  732. 
Salts  of  Oxide  of,  i.  544. 
Sulphides,  i.  541. 
Telluride  of,  ii.  201 


800 


INDEX. 


Solid  Bodies,  Atomic  Volume  of,  i.  209  ; 
ii.  582. 
Expansion  of,  i.  2  ;  ii.  221. 
Specific  Heat  of,  ii.  427. 
Soluble  Glass,!.  568. 
Solution,  Density  of  Salts,  600. 

of   Salts    in   Water,    Calorific 
Effect,  ii.  633. 
Soils,  Estimation  of  Nitrates  in,  ii.  656. 
Spectra  exhibited  by  Coloured  Media,  ii. 

486. 
Specific  Heat,  i.  24  ;  ii.  426. 

and  Heat  of  Combustion, 
Relations  between,  ii.629. 
of  Gases  i.  27. 
Atoms,  i.  135. 
Carbon,  i.  139. 
Gravity  of  Gases  and  Table  of, 

i.  149—155. 
Rotatory  Power,  ii.  469. 
Stannic  Acid,  ii.  137. 

Chloride,  ii.  140. 

Salts,  Reactions  of,  ii.  137. 

Oxide,  ii.  136. 

Oxide,  Sulphate  and  Nitrate  of, 

ii.  142. 
Sulphide,  ii.  139. 
Stannous  Iodide,  ii.  135. 
Oxide,  ii.  131. 
Salts,  Reactions  of,  ii.  133. 
Sulphate  and  Nitrate,  ii.  135. 
Steam  as  a  Moving  Power,  i.  59 — 62. 

Latent  Heat  of,  i.  57  ;  ii.  432. 
Steel,  ii.  31. 
Stoneware,  i.  614. 
Strontia,  i.  579. 

Estimation  of,  ii.  747. 
Separation  of,  from  Baryta,  ii. 
748. 
Lime,      ii. 
752. 
Sulphate,  Hyposulphite,  and  Ni- 
trate of,  Carbonate  of,  i.  580. 
Strontium,  Binoxide  and  Chloride  of,  i. 
580. 
Preparation   and    Properties 
of,  i.  579  ;  ii.  146. 
Subchloride  of  Carbon,  i.  483. 
Subnitrates  or  Bismuth,  ii.  247. 

Copper,  ii.  105. 
Suboxide  or  Bioxide  of  Bismuth,  ii.  241. 
Lead,  ii.  112. 
Silver,  ii.  332. 
Subsalts,  i.  194. 
Substances,  Table  of  Elementary,  i,  108 

-112. 
Substitution,  Formation   of  Compounds 

by,  i.  227. 
Subsulphide  of  Iron,  ii.  38. 


Succinate,  Ferric,  ii  51. 

Sugars,  Optical  Rotatory  Power  of,    ii. 

469-475. 
Sulphamide,  ii.  741. 
Sulphantimonic  Acid,  ii.  232. 
Sulphate  and  Nitrate  of  Stannic  Oxide, 
ii.  142. 
Ceroso-ceric  ii.  264. 
Cerous,  ii.  266. 
Chromic,  ii.  159. 
Chromous,  ii.  1 55. 
Cupric,  ii.  103. 
Ferric,  ii.  50. 
Ferroso- Ferric,  ii.  51. 
Ferrous,  ii.  41. 
Iridic,  ii.  397. 
Manganic,  ii.  11. 
Manganous,  ii.  8. 
Mercuric,  ii.  320. 
Mercurous,  ii  301. 
of  Alumina,  i.  605. 
Ammonium,  ii.  739. 
Antimony,  ii.  226. 
Bismuth,  ii.  247. 
Cadmium,  ii.  91. 
Didymium,  ii.  275. 
Didymium,  Solubility  of,  ii. 

276. 
Lanthanum,  ii.  272. 
Lead,  ii.  121. 
Lime,  i.  589. 

and  Potash,  ii.  751. 
Magnesia,  i.  597. 
Nickel,  ii.  76. 
Potash,  i  534. 

and  Soda,  ii.  735. 
Rhodium,  ii.  410. 
Silver,  ii.  339. 
Soda,  Solubility  of,  ii.  735, 
Strontia,  i.  584. 
Titanic  Acid,  ii.  149. 
Uranyl,  ii.  257. 
Zinc,  ii.  85. 
Osmic,  ii.  401. 
Potassio-Ferric.  ii.  50. 
Stannous,  ii.  135. 
Ruthenic,  ii.  416. 
Uranic,  ii.  257. 
Uranous,  ii.  254. 
Sulphates,  i.  409. 

Earthy,  decomposition  of,  by 
Alkaline  Carbonates,  ii.  597. 
Formula;  of  Neutral,  i.  190. 
Atomic  Volume  of  First  and 
Second  Class,  i.  214. 
Sulphide,  Auric,  ii.  355. 
Aurous,  ii.  350. 
Cuprous,  ii.  96. 
Ferric,  ii.  47. 


INDEX. 


801' 


Sulphide,  Ferrous,  ii.  37. 

Mercuric,  ii.  307. 
Mercurous,  ii.  298. 
Staunic,  ii.  139. 
Stannous,  ii.  133. 
of  Aluminium,  i.  604. 
Carbon,  solid,  i.  427. 
Didymium,  ii.  274. 
Lead,  ii.  116. 
Manganese,  ii.  5. 
Nitrogen,  i.  424  ;  ii.  682. 
Rhodium,  ii.  409. 
Silver,  ii.  336. 
Tantalum,  ii.  283. 
Zinc,  ii.  84. 
Sulphides,  Alcoholic,  ii.  546. 

Classification  of,  ii.  546. 
of  Ammonium,  ii.  737. 
Arsenic,  ii.  209. 
Carbon,  i.  425  ;  ii.  684. 
Cobalt,  ii.  67. 
Iridium,  ii.  395. 
Molybdenum,  ii.  192. 
Osmium,  ii.  405. 
Phosphorus,  i.  454  ;  ii.  695. 
Potassium,  i.  527. 
Ruthenium,  ii.  417. 
Tellurium,  ii.  200. 
Tungsten,  ii.  182. 
Sulphite,  Chromous,  ii.  155. 
Cuprous,  ii.  98. 
of  Cadmium,  ii.  90. 
Didymium,  ii.  276. 
Perchloride  of  Carbon,  ii.  703. 
Protochloride  of  Carbon,  ii. 

704. 
Soda,  i.  554. 
Sulphites,  Mercuric,  ii.  321. 
their  uses,  i.  401. 
Sulphobromide  of  Phosphorus,  ii.  711. 
Sulphocarbonic  Acid,  i.  425. 
Sulphochloride  of  Mercury,  ii.  313. 
Sulphocyanide  of  Aluminium,  i.  605. 
Platinum,  ii.  371. 
Potassium,  i.  532. 
Sulphur,  AUotropic   modifications   of,   i. 
396  ;  ii.  679. 
and  Carbon,  i.  425 ;  ii.  684. 
Chlorine,  i.  485  ;  ii.  706. 
Hydrogen,  i.  419. 
Nitrogen,  i.  424  ;  ii.  682. 
Phosphorus,  i.  454  ;  ii.  695. 
Bromide  of,  i.  490. 
Chlorides  of,  i.  485  ;  ii.  706. 
Class  of  Elements,  i.  168. 
Estimation  of,  ii.  686. 
Heat    of,    Combustion    of,    in 

various  states,  ii.  630. 
Iodide  of,  i.  502. 


Sulphur,  Melting  Point  of,-  i.  396  ;   ii. 
681. 
Properties  of,  i.  396. 
Protochloride  of,  i.  486. 
Uses  of,  i.  398. 
Sulphur- Acids,  ii.  547. 
Sulphur- Compounds,  Atomic  Volume  of 

Liquids,  ii.  577. 
Sulphur- Ethers,  Compound,  ii.  543. 
Sulphur-Salts,  ii.  548. 
Sulphuric  Acid,    Action   of,   on   Penta- 
chloride  of  Phospho- 
rus, ii.  709. 
Density  of,  i.  408. 
Estimation  of,  ii.  686. 
Formation   of,    Anhy- 
drous, ii.  682. 
Heat    evolved   in   the 
Hydration  of,  ii.  632. 
Hydrates  of,  i.  409. 
Manufacture  of,  i.  404. 
Preparation  of,  i.  402. 
Properties  of,  L  406. 
Uses,  i.  410. 
Sulphurous  Acid,  Action  of,  on  Penta- 
chloride  of  Phospho- 
rus, ii.  708. 
Estimation  of,  ii.  687. 
its  Preparation,  i.  399. 
Properties  of,  i.  400. 
Series,  i.  402. 
Volumetric  Estimation 
of,  ii.  722. 
Water,  i.  369. 
Sulphuryl,  Chloride  of,  ii.  550,  709. 
Supersaturated  Solutions  of  Carbonate  of 
Soda,  ii.  732. 

Sulphate  of,  i.  555. 
Symbols,  i.  118. 


T. 


Tangent- Compass,  ii.  497. 
Tantalic  Acid,  ii.  278. 

Hydrated,  ii.  280. 
Reactions  of,  ii.  287. 
Tantalous  Acid,  ii.  273. 
Tantalum,  ii.  277. 

Bromide  of,  ii.  284, 
Chloride  of,  ii.  283. 
Estimation  and  Separation  of, 

ii.  284. 
Fluoride  of,  ii.  284. 
Sulphate  of,  ii.  283. 
Tartar- emetic,  ii.  226. 
Tartaric  Acid,  Circular  Polarisation   of, 
ii.  477. 
Inactive,  ii.  480. 


802 


INDEX. 


Tartaric  Acid,  Pyro-electricity  of,  ii.479. 
Tartrate  of  Potash  and  Antimony,  ii.226. 

Potassio- ferrous,  ii.  43. 
Tartrate  of  Tin  and  Potassium,  ii.  135. 
Telluretted  Hydrogen,  ii,  200. 
TeUuric  Acid,  ii.  198. 

Anhydrous,  ii.  199. 
Tellurides,  ii.  201.  546. 
Tellurium,  ii.  194. 

Chlorides  of,  ii.  200. 
Estimation  and  Separation  of, 

ii.  201. 
Sulphides  of,  ii.  200. 
Tellurous  Acid,  ii.  196. 

Anhydrous,  ii.  196. 
Temperature,  Capt.  Parry  and  Back  on, 
i.  41. 
Equilibrium  of,  i.  38. 
of  the  Atmosphere,  i.  325. 
Table   of  interesting  Cir- 
cumstances in  the  Range 
of,  i.  23. 
Tension  of  Vapours,  ii.  434. 
Terbia,  i.  618. 
Terbium,  i.  617. 

Terchloride  of  Antimony,  ii.  225. 
Bismuth,  ii.  245. 
Bismuth  and  Ammonium, 

ii.  246. 
Iridium,  ii.  397. 
Osmium,  ii.  403. 
Phosphorus,  i.  486. 
Terchromate  of  Potash,  ii.  166. 
Terfluoride  of  Antimony,  ii.  225. 
Chromium,  ii.  169. 
Teriodide  of  Bismuth,  ii.  246. 
Teroxide  of  Bismuth,  ii.  242. 
Hydrogen,  ii.  640. 
Iridium,  ii.  395. 
Tersulphide  of  Antimony,  ii.  223. 

Bismuth,  ii.  244. 
Test-  Acid,  i.  550. 

Tetramercurammonium,  Chloride   of,  ii. 
312. 
Iodide  of,  ii.  307. 
Nitrate  of,  ii.  322. 
Tetrametaphosphoric  Acid,  ii.  694. 
Tetrathionic  Acid,  i.  418. 
Tetartohedry,  ii.  476. 
Thenardite,  i.  557. 
Thionamic  Acid,  ii.  741. 
Thionamide,  ii.  709,  741. 
Theory  of  Heat,  Dynamical,  ii.  449. 
Thionyl,  Chloride  of,  ii.  708. 
Thermometer,  Celsius,  i.  18. 

Crichton's,  i.  17. 
Description  of  the,  i.  14. 
Regnault's    and    Pierre's 
Remarks  on  the,  i.  1 7. 


Thermometer,  Reaumur's,  L  18. 
Rutherford's,  i.  21. 
Sanctorio's  and  Sir  John 

Leslie's,  i.  14. 
Six's,  i.  22. 
Thermo-multiplier,  i.  35. 
Thorina,  i.  618. 
Thorium,  i.  615.  618. 
Tin,  ii.  130. 

Alloys  of,  ii.  143. 
AmmoniO' Chloride  of,  ii.  140. 
and  Antimony,  Separation  of,  ii.  238. 
Potassium,  Bichloride  of,  ii.  1 42. 
Protochioride  of,  ii, 

134. 
Tartrate  of,  ii.  135. 
Sulphur,  Bichloride  of,  ii.  141. 
Bichloride  of,  with  Oxychloride  of 

Phosphorus,  ii.  142. 
Bichloride  of,  with  Pentachloride  of 

Phosphorus,  ii.  141. 
Bioxide  of,  ii.  136. 
Bisulphide  of,  ii.  139. 
Chlorosulphide  of,  ii.  141. 
Class,  i.  173. 
Estimation   and   Separation   of,    ii. 

143. 
Protochioride  of,  ii.  133. 
Protiodide  of,  ii.  135. 
Protoxide,  ii.  131. 
Protosulphateof,  ii.  135. 
Protosulphide  of,  ii.  133. 
Separation  of,  from  Antimony  and 

Arsenic,  ii.  236. 
Sesquioxide  of,  ii.  136. 
Volumetric  Estimation  of,  ii.  144. 
Tinkal,  i.  565. 

Titanic  Acid,  Sulphate  of,  ii.  149. 
Titanic  Oxide,  ii.  147. 
Titanium,  ii.  145. 

Bichloride  of,  ii.  148. 
Bifluoride  of,  ii.  149. 
Bisulphide  of,  ii.  148. 
Bromide  of,  ii.  149. 
Estimation  and  Separation  of, 

ii.  151. 
Nitrides  of,  ii.  149. 
Nitro-cyanide  of,  ii.  150. 
Protoxide  of,  ii.  146. 
Sesquioxide  of,  ii.  147. 
Touchstone,  ii.  362. 
Tourmalines,  Polarisation  by,  ii.  461. 
Transpiration  of  Gases,  i.  83. 
Triamides,  Primary,  ii.  559. 
Tribasic  Phosphate  of  Water,  i.  440. 

Salts,  i.  194. 
Trimetaphosphoric  Acid,  ii.  694. 
Trimercurammonium,  Nitrate  of,  ii.  323. 
Triphosph amide,  ii.  695. 


INDEX. 


803 


Trisul-hyposulphuric  Acid,  i,  418. 
Trithionic  Acid,  i.  417. 
Tungstates,  ii.  180. 

and  Chromates,  Atomic  Vo- 
lume of,  i.  214. 
Tungsten,  ii.  176, 

Class  of  Elements,  i.  173. 
Chlorides  of,  ii.  183. 
Estimation  and  Separation  of, 

ii.  184. 
Phosphides  of,  ii.  182. 
Sulphides  of,  ii.  182. 
Tungstic  Acid,  ii.  178. 

Action  of,  on  Pentachloride  of 

Phosphorus,  ii.  710. 
Oxide,  ii.  177. 
Turnbull's  Blue,  ii.  40. 
Type-Metal,  ii.  234. 
Types  and  Radicals,  ii.  521. 


U. 


Ultramarine,  i.  573. 
Unitary  System,  Gerhardt's,  ii.  512. 
Uranic  Nitrate,  ii.  257. 
Oxide,  ii.  255. 
Oxide,  Compounds  of,  with  Bases, 

ii.  258. 
Phosphates,  ii.  257. 
Salts,  Fluorescence    of,   ii.   257, 

484. 
Sulphate,  ii.  257. 
Uranium,  Estimation  and  Separation  of, 
ii.  258. 
Sources  and  Extraction  of,  ii. 

251. 
Protochloride  of,  ii.  254. 
Protoxide  of,  ii.  253. 
Sesquioxide  of,  ii.  255. 
Ui-anoso-uranic  Oxide,  ii.  254. 
Uranous  Chloride,  ii.  254. 
Oxide,  ii.  253. 
Sulphate,  254. 
Uranyl  and  Potassium,  Chloride  of,  ii. 
257. 
Arseniate  of,  ii.  258. 
Chloride  of,  ii.  256. 
Nitrate  of,  ii.  257. 
Phosphates  of,  ii.  257. 
Sulphate  of,  ii.  257. 
Utricular  Sulphur,  ii.  681. 


V. 

Vanadic  Acid,  ii.  174. 
Vanadium,  ii.  173. 

Bioxide  of,  ii,  173. 


Vanadium,  Estimation  and  Separation  of, 
ii.  175. 
Protoxide  of,  ii.  173. 
Vaporisation,  i.  47 — 68. 

Brix's  Experiments   on,  i. 

56,  67. 
Despretz's  Experiments  on, 

i.  57. 
Table  of  Elastic  Force  of 
Steam,  i.  55. 
Vapour,  i.  328. 

of  Water,  i.  314. 
Vapours  and  Gases,  Specific  Heat  of,  ii. 
429." 
Table  of  the  Specific  Gravity 

of  Gases  and,  i.  149,  155. 
Latent  Heat  of,  ii.  431. 
Tension  of,  ii.  434. 
of  Saline  Solutions,  Tension  of, 
ii.  437. 
Vapour-volume,  Uniformity  of,  ii.  515. 
Varvicite,  ii.  14. 
Ventilators,  Charcoal,  ii.  659. 
Voltaic  Circle,  Applicationof  the,  to  Che- 
mical Synthesis,  i.  264. 
(Compound),  i.  250. 
Liquid  Elements   of  the, 

i.  258. 
(Simple),  i.  242. 
Solid    Elements    of  the, 

i.  255. 
■without  a  Positive  Metal, 

i.  267. 
with       the       Connecting 
Wire  unbroken,  i.  245. 
with      the       Connecting 

Wire  broken,  i.  249. 
Theoretical       Considera- 
tions on,  i.  272. 
Battery,  i.  253. 

Current,  Heating  Power  of,  ii.  506. 
Endosmose,  i.  266. 
Instruments,  i.  283,  290. 
Protection  of  Metals,  i.  256. 
Secondary  Decomposition,  i.  262. 
Transference  of  Ions,  i.  265. 
Voltameter,  L  290. 
Volume,  Atomic,  of  Liquids,  ii.  569. 
Volume,  Atomic,  of  Solids,  i.  213 ;  ii.  582. 
Volumetric  Analysis,  Bunsen's  General 

Method  of,  ii.  722. 
Volatility  of  Carbon,  ii.  658. 

W. 

Water,  Absorption  of  Gases  by,  i.  75. 
316;  ii.  647. 
Boutigny's  Experiments  on  the 
Ebullition  of,  i.  49. 


804 


INDEX. 


Water,  Calorific   Effect  of  Solution  of 
Salt§  in,  ii.  633. 

Calprimeter,  ii.  626. 

Capacity  of,  for  Heat,  i.  26. 

Chalybeate,  i.  319. 

Circulation  of,  i.  11. 

Constitutional,  i.  195. 

Contraction  of,  i.  9. 

Ebullition  of,  i.  48, 

Estimation  of,  ii.  646. 

Expansion  of,  i.  1 1  ;  ii.  424. 

Estimation  of  Nitrogen  in,ii.  656. 

Evaporation  of  (Dalton),  i.  91. 

Filter,  i.  317. 

Heat  evolved  in  the  combination 
of  Sulphuric  Acid  with,ii.  632. 

Latent  Heat  of,  i.  44  ;  ii.  430. 

Vapour  of,  i.  44  ; 
ii.  432. 

Leslie's  Process  for  Freezing  of, 
i.  66. 

Oxygenated,  i.  185. 

Properties  of,  i.  313. 

Saline,  i.  319. 

Schweitzer's     Analysis    of  Sea- 
Water,  i.  319. 

Specific  Heat  of,  ii.  428. 

Sulphurous,  i.  319. 

Table  of  Boiling  Point  of,  i.  52. 

Tension  of  Vapour  of,  i.  65  ;  ii. 
435. 

Tribasic  Phosphate  of,  i.  440. 

Type,  ii.  523,  530. 

Uses  of,  i.  316. 

Vapour  of,  i.  314. 


Wedgwood's  Pyrometer,  i.  20. 

White  Lead,  ii.  119. 

Williamson's  Theory  of  Chemical  Action, 

ii.  600. 
Winds,  i.  326. 
Wood,  Heat-conducting  Power  of,  ii.  443. 


Y. 

Yellow  Prussiate  of  Potash,  i.  529. 
Yttria,  i.  617. 
Yttrium,  i.  615,  617. 


Z. 


Zinc,  i.  128,  256;  ii.  81. 

Alloys  of,  ii.  87. 

Carbonate  of,  ii.  85. 

Chloride  of,  ii.  84. 

Estimation   and   Separation  of,  ii. 
87. 

Iodide  of,  ii.  85. 

Nitrate  of,  ii.  86. 

Oxide  of,  ii.  84. 

Phosphate  of,  ii  86. 

Plates,  Amalgamation  of  the,  i.  246. 

Silicate  of,  ii.  87. 

Sources  and  Extraction  of,  ii.  81. 

Sulphate  of,  ii.  85. 

Sulphide  of,  ii.  84. 
Zincoid,  i.  254. 
Zirconia,  i.  619. 
Zirconium,  i.  615,  619. 


ERRATA  IN  VOL.  IL 


Page 

Line 

92 

5  from  top 

for 

Cor  dHg, 

read 

CdHg,. 

110 

9  from  bottom 

»> 

cadium 

„ 

cadmium. 

142 

11 

» 

sulphide 

»» 

sulphides. 

143 

17  from  top 

„ 

Odlings 

»> 

Odling 

539 

15 

" 

p,nA|^^ 

»> 

Hz      J     ' 

541 

^ 

M 

AsH.O^ 

» 

AsH^O,. 

LONDON  : 

PKINTKD   BY    SPOTTISWOODE  AND  CO. 

NKW-SXREKT  SQUARE. 


^   H.    B^ILIilERE'S 

CATALOGUE    OF 

MCENT  FOEEIGN  BOOKS 


CHEMISTRY,  ELECTRICITY,  PHYSICS, 

METEOEOLOGY,  Ac,  &o. 


Accvtm.    Treatise  on  the  Art  of  Brewing.    12mo.    London    ,  .  • 

Treatise  on  Gas  Ligliting.     lloyal  8vo.    London 

Acken  (A.)    Arts  and  Manufactures,  illustrated  witli  historical  and  literary  details.    8vo. 
half  calC     London,  18-')l-46  ...... 

Aime,  (Martin).     Lettres  a  Sophie  sur  la  Physique.     12nio.     Paris,  1843 

Aja.»>»on  de  <«run(]»ii.eriie*  NouveauManuelcompletdeChimieapphqueealaMede 
cine.     ISnio.     Paris,  1882  ...... 

Ajasson  de  i^randsag'nc  et  Foiiclie.  Nouveau  Manuel complet  de  Physique  et 
de  Meteorologie.     2d  edit.     ISmo.     Paris,  1886         .... 

An  Explanatory  l>ictionary  of  the  Apparatus  and  instruments  employed  in  the 
various  operations  of  Philosophical  and  Experimental  Chemistry.  17  Plates.  8vo.  Lon^ 
don. 1824  ........ 


2  76 

8  60 

8  00 

8T 

87 
87 

1  00 


Aunales  de  CliiniiC)  ou  llecueil  de  Memoires  concernant  la  Chimie  et  les  Arts  qui 
en  dependent.     Paris,  17S9  to  1815  inclusive.     8vo.,  et  3  vols,  de  Tables. 
2e  Serie,  1816  to  184(1,  incl.    75  vols.,  8vo.  et  8  vols,  de  Tables. 

8e  Serie,  1841  to .     Cette  sene  est  en  cours  de  publication. 

Prix  par  annee  .  .  .  .  .  ,  ,  .  11  25 

Aunuaire  de  Ctiimie,  comprenant  les  applications  de  cette  Science  a  la  Medecine  et 
a  la  Pharmacie,  ou  Repertoire  des  decouvertes  et  des  nouveaux  travaux  en  chimie  faits 
dans  les  diverses  parties  de  I'Europe.  Par  MM.  E,  Millon,  J.  Reiser.  Avec  la  collabora- 
tion de  MM.  F.  Hoefer  et  J.  Nickles.    Svo.    Paris,  1846-51.    7  vols.  .  .  .  14  00 

Arag'O*     tEuvres  completes. 

Meteorological  Essays.    With  an  Introduction  by  Humboldt.    Edited  by  Col. 

Sabine.    8vo.    London,  1856        .  .  .  .  .  .  .    5  50 

Arcliambanlt.  Precis  Elementaire  de  Physique.  Premiere  partie,  comprenant  la 
Pesanteur,  I'Hydrostatlque  et  la  Chaleur,  avec  98  gravures  intercalees  dans  le  texte. 
1854.    12mo.     .  .  .  .  .  .  .  .  .    1  00 

. Deuxieme  partie,  comprenant  I'Electricite,  le  Magnetisme,  le  Galvanisme,  I'Elec- 

tfo-dynamique,  I'Acoustiqueetl'Optique,  avec  142  gravures  dans  le  texte.    1855.    12mo.    100 

Araott  (A.)    The  Smokeless  Fire-place,  Chimney  Valve,  and  other  means,  New  and  Old, 

of  obtaining  Healthful  Warmth  by  Ventilation.    8vo.    London,  1855  .  .    1  80 

Avog'adro.     Sui  calori  Speafico  de  Corpi  Solidi  e  liquidi.    4to.  .  .  .75 

Barreswril  et  Davannc.  Chimie  Photographique,  contenant  les  elements  de  Chimie 
expliques  par  les  manipulations  Photographiques.  Les  procedes  de  Photographic  sur 
Plaques,  sur  Papier  sec  ou  humide,  sur  Verres  au  Collodion  et  a  I'Albumine.  La  maniere 
de  preparer  soi.  meme,  d'employer  tous  les  reactifs  et  d'utiliser  les  residus,  Les  Re- 
cettes  les  plus  nouvelles  les  derniers  perfectionnements.  La  Gravure  et  la  Lithophoto- 
graphie.    Svo.    1854     .  .  .  .  .  .  .  .    1  50 

Barreswil  et  Sobrino*  Appendice  a  touts  les  traites  d'Analyse  Chimique,  recueil 
des  observations  publiees  depuis  10  ans  sur  PAnalyse  qualit.  et  quant.  1  vol.,  Svo. 
Paris,  1842       .  .  .  .  .  .  .  .  .    1  75 

Barrii'-l  (CI.)    Traite  de  Chimie  Technique  appliqiieeaux  Arts  et  a  PIndustrie,a  la  Phar- 
macie et  a  1' Agriculture.    Tome  ler.    Svo.    Paris,  IS56        ,  .  .  .    1  75 
L'ouvrage  aura  6  vols. 

Baudrimont  (A.)  Traite  de  Chimie  Generale  et  Experimentale,  avec  les  applications 
aux  Arts,  a  la  Medecine,  a  la  Pharmacie,  &c.,  accompagne  de  200  planches  intercalees 
dans  le  texte.    2  forts  vol.  in-8.    Paris,  1844-46      .  .  .  .  .4  60 

jy.  BaiUiere,  290  Broadway,  JT.  ¥*. 


f2  Standard  Scientific  Works, 


Baudrimont  (A.)    Du  sucre  et  de  sa  fabrication,  suivi  d*un  precis  de  la  legislation 

qui  regit  cetl€  industrie,  par  A.  Trebuchet.    9vo.,  avec  21  flg.    Paris,  1841        ,  .    0  75 

Becqnerel.    Traite  d'Electricite  et  de  Magnetisme,  et  des  Applications  de  ces  Sciences  a 

la  Chiniie,  a  la  Physiolugie  et  aux  Arts.    8  vols.    8vo.,  plus  planches.    Paris,  1856  .    6  00 

Ouvrage  termine.  11  est  I'expose  des  lecons  qui  sont  faites  au  Museum  d'histoire  natu- 
relle  et  au  Cftaservatoire  des  arts  et  metiers  sur  I'electricite,  le  magnetisme  et  toutes 
leurs  applications.  Chaque  volume  renferme  les  applications  relatives  au  sujet  principal 
qui  s'y  trouve  traite.  Les  figures,  dessinees  et  gravees  avec  soin,  snot  intercaleea  dans 
le  t«xte. 


Traite  de  TEIectricite  et  du  Magnetisme.    7  vols.,  8vo.,  avec  atlas  in-foL    Paris. 


]8a4  .  .  .  .  .  .  .  .  .  .  20  00 

■  Traite  complet  du  Magnetisme.    Svo.  .  .  .  .  <    2  50 

— — ^    Elements  d'Electro-Chimie  Appliques  aux  Sciences  Naturelles  et  aux  Arts.    Svo. 

Paris,  1818        .  .  .  .  .  .  .  .  .    2  00 

Becquerel  (in.  A.)    Des  Applications  de  I'Electricite  a  la  Pathologie.    8vo.    Paris,  1856 
Bernay  (A.  J.)    First  Lines  in  Chemistry :  a  Manual  for  Students.    12mo.    London, 

1856  .  .  .  .  .  .  .  .  .  .    2  12 


Household  Chemistry,  or  the  Rudiments  of  the  Science  applied  to  every-day  life. 


12mo.    London,  1852      .  .  .  .  .  .  ,  .11* 

Berthier.    Traite  des  Essais  par  la  Voie  Seche,  ou  des  proprletes,  de  la  composition  et  de 

I'essai  des  Substances  Metalliques  et  des  Combustibles.    2  vols.,  8vo.    15  pi.    Paris,  1848    8  00 
Bertliollet.     Art  of  Dyeing  and  Bleaching  by  Ure.    8vo.    London    .  .  .    3  60 

Berzelins.    Traite  complet  de  chimie  minerale,  vegetale  et  animale,  seconde  edition  fran- 

caise,  traduit,  avec  I'assentiment  de  I'auteur,  par  M.  Esslinger  et  P.  Hoefer.    Paris, 

1846-61.    Vol.  1  to  6      ,  .  .  .  .  .  .  .  18  00 

See  Crerbardt. 
' Rapport  annuel  sur  les  progres  de  la  chimie,  presente  le  80  mars  de  chaque  annee, 

a  I'Academie  des  Sciences  de  Stockholm,  traduit  du  Suedois,  par  Plantamour,    8  vols. 

8vo.    Paris,  1S41  to  1848  .  .  .  .  .  .  .9  00 


View  of  Animal  Chemistry.    Svo.    London    ,  .  .  .  , 

Use  of  the  Blowpipe,  translated  by  Children.    Svo.    London.    (Very  scarce.)       . 
Traite  de  Chimie.    Nouv.  edit.,  par  B.  Valerius.    4  vols.,  gr.  8vo.,  avec  8  planches. 


Half  bound,  cf.    Bruxelles,  1841  to  1844    . 
Lehrbuch  der  Chemie.    Funfte  auflage.    Bds.  1-5.    Dresden,  1842-48 


Billard.    Traite  de  la  fabrication  du  Platine.    Svo.,  d'une  feuille  et  quart.    Paris,  1855  .    2  60 
Biot.     Instructions  pratiques  sur  I'observations  et  la  mesure  des  proprietes  optiques  ap- 
pelees  rotatoires,  avec  I'expose  succinct  de  leur  application  a  la  chimie  medicale  scien- 
tifique  et  industrielle.    Paris,  1845  .  .  .  .  .  .    0  25 

Precis  elementaire  de  Physique.    2  vols.,  Svo.    Paris,  1825        .  .  .    5  00 

• Traite  de  Physique  Experimentale.    4  vols.,  Svo.    Paris.    (Very  scarce.) 

De  la  Polarisation  de  la  Lumiere.    1  vol.,  4to.    Planches.    (Scarce.) 

Bird  (G.)    Elements  of  Natural  Philosophy,  being  an  Experimental  Introduction  to  the 

study  of  the  Physical  Sciences.    12mo.,  cloth  .  .  .  ,  .8  75 

Biscbofl*.    Elements  of  Chemical  and  Physical  Geology.    Translated  by  Paul  and  Drum- 

mond.    2  vols.,  Svo.    London,  1854-56       .  .  .  .  .  .    9  00 

Blancbiment.    Nouveau  Manuel  complet  du  Blanchiment,  du  Blanchissage,  Nettoyage 

et  Degraissage  des  fils  et  Etoffes  de  Coton,  Chanvre,  Lin,  Laine,  Sole,  etc.    2  vols.,  18mo. 

Paris,  1856        .  .  .  .  .  .  .  .  .    1  60 

Black  (W.)    Practical  Treatise  on  Brewing.    4th  edit.    Svo.    London,  1849    .  .    8  25 

Blanquart  (Evrard.)    Traite  de  Photographic  sur  Papier.    Svo.    Paris.  1851  .    1  25 

Blowpipe.    See  Sanders,  Dr.  J.  M. 

Boucbardat.     Opuscules  d'Economie  Rurale.    Svo.    Paris,  1851        .  .  .    1  00 

Bouqnet  (J.  P.)    Histoire  Chimique  des  Eaux  Minerales  et  Thermales  de  Vichy.    Cusset, 
Vaisse,  Hauterive  et  Saint- Yorre ;  Analyses  Chimiques  des  Eaux  Minerales  de  Medagup, 
Chateldon,  Brugheas  et  Seuillet.    Svo.,  8  cartes.    Paris,  1855  .  .  .    1  75 

Boussingault.     Rural  Economy  ;  in  its  Relations  with  Chemistry,  Physics,  and  Meteor- 
ology.   2d  edition,  with  notes  carefully  revised  and  corrected.    1  vol.,  Svo.,  cloth,  bds. 
London,  1845    .  .  .  .  .  .  ...  .    4  50 

Boutet  de  ITIon vel*     Cours  de  Chimie,  redige  conformement  aux  derniers  programmes 
de  I'Enseigneraent  Scientifique  dans  les  Lycees,  et  a  celuj  du  Baccalaureat  des  Sciences, 
avec  118  gravures  intercalees  dans  le  texte.    12mo.    Paris,  1856        .  .  .    1  25 

Boutigny.    Base  d'une  Nouvelle  Physique,  I'etat  Spheroidal.    Svo.    1842       .  .    1  25 

Bdviuan  (jr.  E.)    Introduction  to  Practical  Chemistry.    2d  edit,    12mo.       .  .    2  00 

Rrande.    Tables  of  Chemical  Equivalents.    Svo.    London     .  .  .  .100 

• Dictionary  of  Science,  Literature,  and  Art.    Svo.    London       .  .  .    7  60 

Tables  of  Specific  Gravity  and  Equivalents.    Svo.        .  .  .  .    2  50 

'  Lectures  on  Organic  Chemistry,  as  applied  to  Manufactures,  Dyeing,  Tanning, 

Ac,  Ac,  arranged  by  Scoflfern.    12mo.    London      .  .  ,  »  .2  25 

Jl.  BaiUierey  1290  Broadway,  J^.  Y\ 


Statidard  Scientific   Works. 


Bl>a,nde(W.  T  )    Manual  of  Chemistry.    2  vols.,  8vo.    London  .  .  .18  60 

Brebisson  (A,  de).      Nouvelle  Methode  Photographique  sur  collodion  donnant  des 

epreuves  instantanees;  traite  complet  des  divers  procedes.     Svo.     Paris,  1852  .  .    100 

Traite  Complet  de  Pliotos^raphie  sur  Collodion  ;  repertoire  de  la  plupart  des  Pro- 
cedes  Counus.    Svo.     Paris,  1855  .  .  .  .  .  .    1  00 

Brewster  (Sir ».)    A  Treatise  on  Optics.    12mo.     London,  1853       .  .  .    1  12 

The  Stereoscope ;  its  History,  Theory,  and  Construction,  with  its  application  to  the 

fine  and  useful  Arts  and  to  Education.    12mo.     London,  1856  .  .  . "  1  62 

Brown  (A.)     The  Philosophy  of  Physics,  or  Process  of  Creative  Development.    Svo. 

New  York,  1854  .  .  .  .  .  .  .  .    2  25 

Cabart  (C)    Legons  de  Physique  et  de  Chimie.    8vo.,  avec  23  planches.    Paris,  1854      .    2  00 
€allours  (A.)     Logons  de  Chimie  Generale  Elementaire,  Professees  a  I'Ecole  Centrale 

des  Arts  et  Manufactures.    Avec  gravures  sur  bois  intercalees  dans  le  texte,  et  planches. 

2vols.,  18mo.    Paris,  1855  .  .  .  .  .  •  .8  00 

Campbell.     A  practical  Text-Book  of  Inorganic  Chemistry,  including  the  preparations 

of  Substances,  an(.'  their  Qualitative  and  Quantitative  Analyses,  witli  Organic  Analyses. 

12mo.  .  .  .  .  .  .  .  .  .    1  50 

Caoutchouc.     Manuels-Roret.     Nouveau  Manuel  complet  du  Pahricant  d'Objets  en 

Caoutchouc,  en  Gutta-Percha  et  en  Gomme  Factice ;  suivi  de  Documents  Etendus  sur  la 

Fabrication  des  Tissus  Iinpermeables,  des  Toiles  Cirees  et  des  Cuirs  Vernis ;  par  M.  Pau- 

lin  Desormeaux.     1  vol.,  I'imo.,  avec  planches.     Paris,  1855  .  .  ,    1  00 

Cavendii^b  Society's  publications  already  published : 

GR.\HAM'S  Chemical  Reports  and  Memoirs.    Scarce. 

GMELINS.     Handbook  of  Chemistry.     Vols.  1  to  lU,  Svo. 

LEHMAN'S  Physiological  Chemistry.    3  vols,  and  atlas. 

Life  and  Works  of  Cavkndish. 

Life  and  Works  of  Dalton. 

BISCHOPF.    Chemical  Geology.    2  vols. 
Subscription,  $7  per  annum. 

Chalmers   (C.)     Thoughts  on  Electricity,  with  notes   of  Experiments.     Svo.,  cloth. 

Edinburgh, ISol  ,  ,  .  ,  .  .  .  .    1  80 

Chemical  Technolog-y;  or  Chemistry  applied  to  the  Arts  and  to  Manufactures. 
By  Professor  Kuapp  audDrs.  Ilonolds  and  Richardson.  3  vols.,  Svo.  (vol.  1,  2nd  edit.), 
illustrated  with  776  woodcuts  and  14  plates.     London,  1848-55  .  .  .  IS  OO 

The  vols,  can  lie  had  separately. 
Vol.  1.  Fuel  and  its  Applications  (Coal,  Gas,  Oil,  Spermaceti,  &c  ),  and  their  application 

to  purposes  of  illumination,  LighthoU'^es,  &c..  Resin,  Wax.  Turpentine,  Peat,  Wood, 

Stoves,  &c.,  &c.,  in  2  parts,  Svo.,  with  483  engravings  and  4  platen     Price  $9  00. 
Vol.  2.  Glass,  Alum,  Eartlienware,  Cements,  Ac,  &c.,   Manufacture.     8vo.,  with  214 

engravings  and  one  plate.     Price  $4  On. 
Vol.  3.  On  those  brandies  of  Chemical  Industry,  including  the  production  of  Food,  and 

related  to  A;;jriiiilture.      (Bread.  Milk,  Tea,    Coffee,    Sugar,   Tobacco,  Ac.)     With  9 

engravings  and  129  woodcuts.     Price  $5  00 
Chemical  Society,   Quarterly  Journal  and  Transactions  of.    Vols.  1  to  8,  cloth  .  27  60 

VoL  9,  in  course  of  publication.    Subscription  price,  $3  00  per  vol. 

Chemist  (The),  or  Reporter  of  Chemical  Discoveries  and  Improvements,  and  Protector 
of  the  Rights  of  tlie  Chemist  and  Cliemical  Manufacturer.  Elited  l)y  Cliarles  and  John 
Watt.    4  vols.,  Svo.,  cloth.    1840-43  .  .  .  .  .  .  10  00 

A  Monthly  Journal  of  Chemical  and  Physical  Science.     Commencing  October,  1853. 

Price,  per  year  or  volume  .  .  .  .  .  .  .    8  60 

Chertier   (F.   OT.)     Nouvelles  Recherches  sur  les  Peux  d'Artifice.     2me  edit.,  Svo., 

avec  gravures.     Paris,  1^.54         .  .  .  .  .  .  .    2  25 

Chevalier.     Recueil  de  Meinoires  et  de  procedes  nouveaux  contenant  la  Photographic 

sur  plaques  metalllques  et  sur  papier.    8vo.,  half  bound,  calf.     Paris,  1847        .  .     0  75 

Chevalier  (C)    Photographie  sur  Papier,  Verre,  et  Metal.    Galvanoplastie.    Catalogue 

universel    explicatif  et  iliustre  des   appareils  perfectionnes.     8vo.,  avec  3  planches. 

Paris,  1856        .  .  .  .  .  .  .  .  .    0  62 

Chevallier.     Dictionnaire  des  Alterations  et  Falsifications  des  Substances  Alimentaires, 

Medicamenteuses  et  Coramerciaies,  avec  I'lndication  des  Moyens  de  les  Keconnaitre. 

2me  edition,  2  vols.,  Svo.     Paris,  1855        .  .  .  .  .  ,    8  26 

Chevallier,  l<amy,  and  Itobiquct.     Dictionnaire  raisonne  des  denominations 

Chimiques  et  Pharmaceutiques,  contenant  tous  les  termes  employes  en  Chimie,  Ac,  Ac. 

2me  edit.,  tome  ler.     Paris,  1853  .  .  .  .  .  .  .    2  26 

Chevreul.     De  la  Baguette  divinatoire,  du  Pendule,  dit  Exjilorateur,  et  des  Tables  Tour- 

nantes,  an  point  de  vue  d'llistoire,  de  la  Critique  et  de  la  Methode  Experimentale.    Svo. 

Paris,  1854        .  .  .  .  .         '       .  .  .  .     1  25 

The  Principles  of  Harmony  and  Contrast  of  Colors,  and  their  Application  to 

the  Arts.    12mo.,  2nd  edition.    London,  1855  .  .  .  .  .3  75 


De  la  loi  du  Contraste  simultane  des  Couleurs  et  de  ses  Applications.    Svo.,  et  4to. 


Atlas.     Paris,  1839  .  .  .  .  .  .  .  .  12  50 

flr.  BaiUierey  290  Broadway,  Jf.  Y*. 


Startdard  Scientific  Works. 


Claudet.    Nouvclles  Recherches  sur  la  diflPerence  entre  les  Foyers  Visuels  et  Photogeniquea. 

8vo.    Paris,  1851  .  .  .  .  .  .  .  .    0  50 

CleSTg  (S.)    Treatise  on  the  Manufacture  of  Coal  Gas.    4to.    London    .  .  .    8  87 

Codex.     Pharmacopee  Francaise,  redigee  par  ordre  du  gouvernement,  avec  appendice 

therapeutique,  par  Cazenave.    8vo.    Paris,  1837     .  .  .  .  .    2  50 

In  iialf  calf  .  .  .  •  •  .  .  .  .    8  00 

Coloriste.    Nouveau  Manuel  Complet  du  Coloriste,  ou  Instructions  Simplifiees  et  elemen- 

taires  pour  I'enluniinure,  le  lavis  et  la  retouche  des  gravures.    Nouvelle  edition.    18mo., 

avec  8  planches.    Paris,  1856       .  .  .  .  .  .  .    0  75 

Colles.    Nouveau  Manuel  de  la  Fabrication  des  Colles,  comprenant  la  Fabrication  des 

Colles  de  Matieres  Vegetales,  par  M.  Malpeyre.    12u^o.     Paris,  1856    .  .  .    0  60 

Coofcy  (A.  J.)    Cyclopedia  of  Practical  Receipts,  and  collateral  information  in  the  Arts. 

Manufactures,  Professions,  and  Trades;  including  Medicine,  Pharmacy,  and  Domestic 

Economy ;  designed  as  a  comprehensive  supplement  to  the  Pharmacopoeia,  and  general 

bopk  of  reference  for  the  Manufacturer,  Tradesman,  Amateur,  and  heads  of  Families. 

8rd  edition.    8vo.    London,  1S66  .  .  .  .  .  .    8  00 

Cooper  (C.)    Identities  of  Light  and  Heat ;  of  Caloric  and  Electricity.    Svo.    Philadel- 

pliia,  1848         .  .  .  .  ,  .  .  .  .    0  T5 

Cotte,     Observations  Meteorologiques.    4to.  .  .  .  .  .    0  60 

Coulomb.    Methode  de  determindr  rinclinaison  d'une  Aiguille  Aiman tee.    4to.  .    0  25 

Crabb  (G.  A.)     Technical  Dictionary ;  or  a  Dictionary  explaining  the  terms  used  in  all 

Arts  and  Sciences.    12mo.    London,  1851  .  .  .  .  .    3  75 

Cumiuing,  J.    A  Manual  of  Electro  Dynamics.    Svo.    London,  1827  .  .150 

Cuudall  (J» .)    The  Photographic  Primer  for  the  use  of  beginners  in  the  Collodion  process. 

Illustrated  with  a  Photographic  Picture.    2d  edit.     12mo.    London,  1856  .  .    0  81 

C  uvier.     Analyse  de  ses  Travaux  sur  la  Physique  et  la  Chimie.    4to.   .  .  .    0  60 

Daguiu  (P.  A.)  Traite  Elementaire  de  Physique  Theorique  et  Experimentale,  avec  les 
Aj)plicatious  a  la  Meteorologie  et  aux  Arts  Industriels.    Tome  ler.    Avec  800  gravures 

sur  bois  iutercalees  dans  le  texte.    8vo.    Paris,  1856              .               .               .               .  3  00 

nalton  (Jolin),  Life  and  Scientific  Researches  of.  ByW.  C.Henry.  8vo.  London,  1854  3  50 

Chemical  Philosophy.    2  vols.,  Svo.     London                .               .               .               .  9  50 

Daniell  (J.  F.)    An  Introduction  to  the  Study  of  Chemical  Philosophy;  being  a  prepa-  8  00 

ratory  view  of  the  forces  which  concur  to  the  production  of  Chemical  Phenomena.     2nd 
edition.    London,  1843     .  .  .  .  .  .  .  .  7  28 

Very  scarce. 

David  (H.)    Methode  de  Peinture  appliquee  uniquement  a  la  Photographic  de  Portraits. 

2nd  edit.,  8vo.    Paris,  1856  .  .  .  .  .  .  .    0  50 

Davy  (Sir  H.)    Chemical  Philosophy.    Svo.    London  .  .  ,  .    6  60 

Account  of  the  Safety  Lamp  for  Miners.    Svo.    London  .  .  .    1  60 

See  Knapp's  Technology. 

Delamotte  (P.)    The  Practice  of  Photography  :  a  Manual  for  Students  and  Amateurs. 

With  a  Calotype  Frontispiece.    8d  edition  revised.    12mo.    London,  1856        .  .    1  37 

The  Oxymel  Process  in  Photography.     12mo.    London,  1856     .  .  .    0  30 

De  la  Rive  (A.)     A  Treatise  on  Electricity  in  Theory  and  Practice.     2  vols.,  Svo. 

London,  1853-6  .  .  .  .  .  .  .  .  14  00 

• (A,— A.)    Traite  d'Elec*^ricite  Theorique  et  applique.    2  vol.,  8vo.,  avec  260  pi. 

intercalees  dans  le  texte.    Par i.^  1853-1856       .  .        .  .  .  .4  50 

Les  nombreuses  applications  de  I'electricite  aux  sciences  et  aux  arts,  les  liens  qui  I'unis- 
sent  a  toutes  les  autres  parties  des  s,ciences  physiques,  ont  rendu  son  etude  indispen- 
sable au  chimiste  aussi  bieu  qu'au  physicien,  au  geologue  autant  qu'au  physiologiste, 
a  I'ingenieur  comme  au  medecin ;  tons  sont  appeles  a  rencontrer  I'electricite  sur  leur 
route,  tons  ont  besoin  de  se  familiariser  avec  son  etude.    Personne  niieux  que  M.  de 
la  Rive,  dont  le  nom  se  rattache  aux  progres  de  cette  belle  science,  ne  pouvait  pre- 
senter I'exposition   des  conuaissances  acquises  en  electricite  et  de  ses  nombreuses 
applications  aux  sciences  et  aux  arts. 
DesainH  (P.)     Lemons  de  Physique,  a  I'Usage  des  Aspirants  aux  Baccalaureats  et  aux 

Ecoles  du  Grouvernenient.    2  vols.    12mo.    Figures  intercalees  dans  le  texte     .  .2  50 

Descliainps.    Art  (1')  de  Formuler,  contenant:    les  Principes  Elementaires  de  Phar- 

macie,  etc.    1  vol.,  ISmo.,  avec  19  figures  intercalees  dans  le  texte.    Paris         .  .125 

Descloizeaux.     Memoire  sur  la  Cristallisation  et  la  Structure  Interieure  du  Quartz. 
Svo,,  plus  4  pi.    Paris,  1856  ....... 

Deson^e.    Traite  de  Photographie  sur  Toile,  dernier  Perfectionnement.  Svo.    Paris,  1855    0  76 

Disderl,  Manuel  Operatoire  de  photographic  sur  collodion  instantane.  Svo.  Paris,  1854  0  75 
" Renseignements  Photographiques   Indispensables  a  tous.     Svo.,  de  8  feuilles. 

Paris,  1855        .  .  .  .  .  .  .  .  .    1  26 

Dodd  (€J.)  The  Curiosities  of  Industry  and  the  Applied  Sciences.  Svo.  London,  1854  .  1  00 
Dornre.    Nouveau  Manuel  Complet  de  dorure  et  d'argenture  par  la  methode  electro- 

chimique  et  par  simple  immersion  par  M.  M.  Selmi,  de  Valecourt,  Malpeyre,  etc.    Nouv. 

edit.,  tres  augraentee,  ornee  de  figures.    12mo.    Paris,  1856  ,  .  .    0  60 

JSr.  naiUiere,  290  Broadway^  JT.  IT. 


Standard  Scientific    Works. 


1  25 

1  00 

1  50 

50  00 

30  00 

0  75 

Dove  (W,  W.)  The  Distribution  of  Heat  over  the  Surface  of  the  Globe,  illustrated  by 
Isothermal,  Thermic  Isabaormal,  and  other  Curves  of  Temperature.  4to.,  with  map. 
London, 1S53  .  .  •  .  •  •  •  .    5  00 

J>U  Bois-Reymond.  on  Animal  Electricity,  by  Bence  Jones.    8vo.    London,  1852    .    1  76 

Duhaniel   de  OTEonceau,    Traite  de  la  Fabrique  des  Manoeuvres  pour  les  Vaisseaux 

ou  I'an  de  la  Corderie  perfectionue.    4to.     Paris,  1747  .  .  .  .    3  00 

Dubrunfaut.     Art  of  Distillation  and  Rectification.    12mo.    London.    (Very  Scarce)  . 
l>uiua$«  and  Houssingault,     The  Chemical  and  Physiological  Balance  of  Organic 

Nature:  an  Essay.     12iuo.  .  .  .  .  .  .  .    1  00 

Du  Moncel  (  tt'li.)   Projection  des  Prinoipaux  Phenomenes  de  I'Optique  a  I'aide  des  ap- 

pareils  de  M.  Dubuscq.     Svo.     Paris,  1S55  .'  .  .  .  .50 
Expose  des  Applications  de  I'Electricite.     Tome  ler.    Notions  Technologiques  2me 

edit.,  8vo.,  avec  8  pi.     Paris,  1866.    (Cette  edition  aura  deux  vols  peut-etre  meiue  trois) 
Dumas  (J.)    Essai  de  Statique  Chimique  des  Etres  Organises.    2me  edit.    Paris,  1842    . 

Memoires  de  Chimie.    Avec  7  Planches.    Svo.    Paris,  1S43 

Traite  de  Chimie  appliquee  aux  Arts.    8  vols,  and  4to*  atlas.    Svo.    Paris,  182S-46. 

Very  scarce      .  .  .  .  •  •  • 

Edition  de  Bruxelles.    S  vols,  and  4to  atlas  .... 

Dunn  (H.)    History  of  the  Steam  Jet  as  applicable  to  the  Ventilation  of  Coal  Mines.    Svo. 
Duplais  (P.)    Traite  des  Liqueurs  et  de  la  Distillatit/n  des  Alcools,  ou  le  Liquoriste  et  le 

DistUlaieur  Modernes,  contenant,  etc.    2  vols.,  Svo.    Versailles,  1856  .  .  .    3  75 

Durand(Faug'.)    Nouvelle  Tlieorie  Physique  ou  Etudes  Analytiques  sur  la  Physique 

et  sur  les  actions  Chimique  fondamentales.    Svo.    Paris,  1854  .  .  .75 

Encres.     Nouveau  Manuel  complet  de  la  Fabrication  des  Encres,  teUes  que  Encres  a 

Ecrire,  Chine,  de  Couleur  a  Marquer  le  Linge  &c.    ISmo.     Paris,  1S55  .  .    1  GO 

Etofies  ?mprimoes.     Nouveau  Manuel  Complet  du  fabricant  d'EtolTes  Imprimecs  et 

du  Fabricant  des  papiers  peints,  par  L.  S.  le  Normand.    ISino.     Paris,  1856      .  .        75 

Exliibition  of  1851  (Lectures  on  the  Results  of  the  Great.)  delivered  before  the 

Society  of  Arts,  Manufactures,  and  Commerce  (Dr.  Whewell,  Professor  Ansted,  and 

others).    2  vols.,  post  8vo.,  each  .  .  .  .  .  .  .    2  25 

Faraday  (  ^IT.)    Chemical  Manipulations,  being  Instructions  to  Students  in  Chemistry. 

8vo.    London,  18J7.    (Very  Scarce.)  .....       about    7  50 
Experimental  Researches  in  Electricity.    3  vols.,  Svo.    London,  1S49-55 .  .  13  50 

The  Subject-matter  of  a  Course  of  Six  Lectures  on  the  Non-metallic  Elements. 

12mo.,  cloth.     London,  1853,        .  .  .  .  .  .  .    1  75 

Fa-U  (J.)  Douze  lecons  de  Photographie.  Description  de  precedes  simples  et  faciles,  au 
moyen  desquels  on  obtient,  presque  infailiiblement,  des  epreuves  sur  verre  et  papier. 
ISmo.  .  .  .  .  .  .  .  .  .    0  75 

Fau  et  Clievalier.     Manuel  du  Physicien  preparateur,  ou  description  d'un  cabinet  de 

Physique.    2  vols.,  ISmo.,  with  an  atlas  of  88  plates.    Paris,  1853       .  .  .    8  75 

Fauclier  (Ij.)    Remarks  on  the  Production  of  the  Precious  Metals,  and  on  the  Demoniti- 

zation  of  Gold  in  Several  Countries  of  Europe.    Svo.    London,  1853,  .  .    0  75 

Faure(.ff.J.)  Analyse  Chimique  des  Eaux  du  departement  de  la  Gironde.  Svo.  Bor- 
deaux, 1853      .  .  .  .  .  .  .  .  .    0  75 

Figui«r  (fj  )    L'Alchimie  et  les  Alchimistes  ou  Essai  Historique  et  Critique  sur  la  Philo- 

sopiie  liermetique.     2d  edit.    12mo,     Paris,  1856    .  .  .  .  .100 

Francoeur  (L.  B»)    Elements  de  Technologic  ou  Description  des  precedes  des  Arts.  Svo.    1  25 

1  ranciw  (Cr.  W.)  The  Dictionary  of  Practical  Receipts  ;  containing  the  Arcana  of  Trade 
and  Manufacture,  Domestic  Economy,  Pharmaceutical  and  Chemical  Preparations,  Ac. 
Svo.     London, 1856         .  .  .  .  .  .  .  .     2  50 

Fresenius  (Dr.)    Instruction  in  Chemical  Analysis.    Quantitative.    2d  edit.   Svo.,  cloth. 

1855  .  .  .  .  .  .  .  .  .    4  50 

Instructions  in  Chemical  Analysis.    Qualitative.    4th  edit.    Svo.,  cloth  .  .    2  75 

Fresenius  et  Sacc.      Precis  d'Analyse  Chhnique  quantitative.     ISmo.      Paris,  1S45. 

Precis  d'Analyse  Chimique  qualitative.    1  vol.,  12mo.,  fig.    Paris,  1847.   {Epuise.) 

Fyfe  (A.)     Elements  of  Cliemistry.     Svo.     London     .  .  ,  .  .     7  25 

Manual  of  Chemistry.     12mo.     London  ,  .  .  •  .  .    2  12 

Oalloway  (K.)    The  First  Step  in  Chemistry :  a  New  Method  for  Teaching  the  Elements 

of  the  Science.    2d  edit.    12mo.    London,  1855        .  .  .  .  .150 

. Manual  of  Qualitative  Analysis.    12mo.,  cloth  .  .  .  .    1  12 

. ■    Chemical  Diagrams,  on  four  large  sheets        .  .  .  .  .    1  75 

Galvanoplastie,  Nouveau  Manuel  complet  de  Galvanoplastie,  ou  Elements  d'Electro- 
raetallurgie ;  contenant  I'Art  de  reduire  les  metaux  a  I'aide  du  liuiile  galvanique,  etc.,  par 
Smee.  Augmente  d'apres  MM.  Jacoby,  Spencer,  Eisner,  etc.  Ouvrage  publie  par  B.  de 
Valicourt.    2  vols.,  ISmo.  .  .  .  .  .  .  .    1  25 

JH.  JSaiUiere,  290  Broadway,  JT.  F: 


Standard  Scientific    Works. 


Ganot  (A.)  Traite  Elementaire  de  Physique  Experinientale  et  Appliquee,  et  de  Meteoro- 
logie,  avec  un  reciieil  nombreux  de  i)robleines,  illustre  Ue  500  graviires  sur  boia  inter- 
calees  dans  le  texte.  6e  edition,  auguientee  de  582  gravures  nouvelles.  l&mo.  Paris, 
1856  .  .  .  .  .  .  .  .  .  .    1  75 

Gas.    Knapp's  Chemical  Technology,  or  Chemistry  applied  to  the  Arts:  Fuel  and  its 

Application.    1vol.    In  2  Parts.    Svo.    London,  1856  .  .  .  .    9  W 

This  is  the  most  recent  and  complete  work  on  the  manufacture  of  Gas,  &c. 

Ckus  liightiug  (Journal  of).    Published  in  London  on  the  10th  of  every  month. 

Price  per  year .  .  .  .  .  .  •  •  .    8  TJ 

5  Vols,  are  published. 

Gaudin  (HI.  A.)    Traite  Pratique  de  Photographi<«,  expose  complet  des  procedes  rela- 

tife  au  Daguerreotype.    8vo.,  hf.  bd,  cf.     Paris,  1844  .  .  .  .    1  6C 

Gauss  (C.  P.)    Intensitas  vis  magnetica  terrestris  ad  mensurara  absolutum  revocata. 

4to.    Gottlngae,  1883      .  .  .  .  .  .  .  .    1  5( 

Gavarret  (J.)    De  la  Chaleur  produite  par  les  Etres  Tivants.    12mo.,  avec  41  figures 

dans  le  texte.    Paris,  1855  .  .  .  .  .  .  .    1  5C 

Gerhardt.    Introduction  a  I'Etude  de  la  Chimie  par  le  Systeme  Unitaire.    12mo.    Paris, 

1848  .  .  .  .  .  .  .  .  -  .    1  OC 

■ Precis  de  Chimie  Organique.    2  vjJs..  Svo.    Paris,  1844  .  .  .    4  OC 

In  half  calf  ...  .....    5  OC 

Traite  de  Chimie  Organique.    4  vols.,  Svo.    Paris,  1855-6  .  .  .  10  M 

Ce  Traite  est  une  suite  a  Berzelius.     Ce  celebre  chimiste  etaut  mort  avant  d'avoir  pu 

terminer  son  ouvrage,  M.  Gerhardt,  ancien  professeur  de  chimie  a  Montpellier,  s'est 
charge  de  terminer  son  travail  et  de  le  mettre  au  courant  de  la  science  actuelle. 

Aide-memoire  pour  I'Analyse  Chimique.    12rao.    Paris,  1862     .  .  .    0  75 

Gerhardt  et  Cliancel.    Precis  d'Analyse  Chimique.    12nio.,  avec  48  gravures.    Paris, 

1855  .  .  .  .  .  .  .  .  .  .    1  25 

Glover  (R.  ]TF.)    A  Manual  of  Elementary  Chemistry:  being  a  Class-book.    Illustrated. 

12mo.     London,  1855     .  .  .  .  .  .  .  .    2  00 

Gmelin.     Handbook  of  Chemistry.     Vol.  1  to  6,  Inorganic  Chemistry  .  .  .  14  00 

"  "  Vol.  7  to  10,  Organic  Cliemistry,  each  vol. ,  .    4  50 

The  work  will  be  completed  in  12  vols.    (Cavendish  Society  Publications.) 
Goebel.     Pharmaceutische  Waarenkunde,  mit  Illum'nirten  Kupfern.    2  vols.,  4to.    Eise- 
nach, 1S50         .  .  .  .  .  .  .  .  .  10  00 

Gore  (G.)    Theory  and  Practice  of  Electro-Deposition,  including  every  known  mode  of 

depositing  metals,  etc.    Svo.     London,  1856  .  .  .  .  .    0  £0 

Gorham.     Unfrequented  Paths  in  Optics.     Part  1.  Light  from  a  Pin-hole.    Part  2.  Light 

from  a  Fissure.    Svo.    London,  1855  .  .  .  .  .  .    1  25 

GraliaiU.     Elements  of  Chemistry  ;  including  the  application  of  the  Science  in  the  Arts. 

By  T.  Graham,  F.U.S.  L.  k  E.,  Professor  of  Chemistry  at  University  College,  London. 

2d  edition,  entirely  revised  and  greatly  enlarged,  copiously  illustrated  with  Woodcuts. 

Vol.  1.    1850    .  .  .  .  .  .  .  .  ,    I  00 

Vol.  2.    London  and  New  York,  1857  .  .  .  ,  ,    4  00 

This  work,  which  ranks  among  the  first  on  the  subject,  is  now  compKte. 

Chemical  Catechism.    Svo.    London  .  .  .  .  .    4  75 

Gregory  (Win.)    Bllementary  Treatise  on  Chemistry.    12mo.    Edinburgh,  1855  .    1  50 
Handbook  of  Inorganic  Chemistry.    For  the  use  of  Students.    3d  edition.    12mo. 

London  .  .  ,  .  .  .  .  .  .     1  75 

— — —    Handbook  of  Organic  Chemistry,  for  the  use  of  Students.    4th  edition,  corrected 

and  much  extended.    12mo.    London,  1856  .  .  .  ,  .    }»  62 

Griffin.     Treatise  on  tiie  Use  of  the  Blowpipe.    ISnio.     London.    (Scarce.) 
GriOiu  (J,  J.)     Chemical  Recreation.     Div.  1,  post  Svo.        .  .  ,  .    0  60 

GriffltU(T.)     Chemistry  of  the  Four  Seasons.     12mo.    London,  1858  .  .  .2  25 

Grove  (W.  R.,)    On  the  Correlation  of  Physical  Forces.    3d  edit.    Svo.    London,  1855  .    2  26 
Gruyer  (li.  A.)     Principes  de  Pliilosopliie  Pliysique  pour  servir  de  base  a  la  Motaphy- 

sique  de  la  Nature,  et  a  la  Pliysique  Experimeiitale.     Svo.     Paris,  1845  .  .    1  75 

Guibourt.     Histoire  naturelle  des  drogues  simples,  ou  Cours  'I'histoire  naturelle  professe 
a  I'Ecole  de  Pharmacie,  quatrieme  edition,  augmentee.    4  vo.  ,  Svo.,  avec  600  fig.  inter- 
calees  dans  le  texte.     Paris,  1849  .  .  .  .  .  .    7  50 

Half  bound  in  Paris  .  .  .  .  .  .9  60 

[Cet  ouvrage,  que  tous  les  pharmaciens  considerent  comme  un  Vade-mecum  de  pre- 
miere necessite,  puree  que  la  grande  exactitude  apportee  par  I'auteur  dans  la  descrip- 
tion des  drogues  leur  permet  dedistinguer  les  diverses  especes  et  varietes  qui  se  rencon- 
trent  dans  le  commerce,  ainsi  que  les  falsifications  qu'on  leur  fait  subir.  Cette  quatrieme 
edition  a  ete  soumise  a  une  revision  generiile,  et  les  augmentations  out  ete  telleuient 
importantes,  qu'on  peut  la  considercr  cotnme  un  ouvrage  eutierement  neuf.     C'est  un 
CourH  i'A/mplet  (V  kifttoire  naturelle  pharmaceutique  et  medicale,  que  les  medecins 
con3ult«ront  toujours  avec  fruit.] 
Guitard.     Histoire  de  I'Electricite.    12rao.    Paris,  1854  .  .  .  .    1  00 

Gurney.     Lectures  on  Chemistry.    Svo.    London     .  .  .  ,  .    8  60 

II,  naiUiere,  290  Broadway,  JT.  Y*. 


'9' 


Standard  Scientific  Works. 


Hardy  (R.  W,  H .)    Incidental  Remarks  on  some  principles  of  Light ;  being  Part  8  of 

an  Essay  on  Vision.    8vo.     London,  1856  .  .  .  .  .    1  00 

Hardtviclft  (T.  F.)    A  Manual  of  Photographic  Chemistry,  including  the  Practice  of 

the  Collodion  Process.    2d  edition.    12ino,  cloth.    London  .  .  .    2  00 

Harris  (Sir  W,  S.)    Rudimentary  Treatise  on  Galvanism,  and  the  general  principles 

of  Animal  and  Voltaic  Electricity.    12mo.,  illustrated,  cloth  .  .  .    0  60 

Hassal(A.H.)    Food  and  its  Adulterations.    With  159  illustrations.    Svo.    London, 

1865    .  .  .  .  .  .  .  .  .  .    8  60 

Heath.    Photography.    A  New  Treatise,  theoretical  and  practical,  of  the  Processes  and 

Manipulations  on  Paper  and  Glass.    8vo.    New  York,  1865  .  .  .  .    1  GO 

Hediey  (John).    Practical  Treatise  on  the  Working  and  Ventilation  of  Coal  Mines; 

with  suggestions  for  Improvements  in  Mining.    8vo.,  cloth   .  .  .  .    8  75 

Heniiah  (T.  H.)    The  Collodion  Process.    4th  edition.    12mo.    London,  1865  .    0  80 

Henry  (\%%)    Elements  of  Experimental  Cliemistry.    2  vols.,  8vo.     London      .  .10  00 

Herling  (A.)    Traite  de  Photographic  sur  Collodion  Sec.    2e  edition.    12mo.    Paris,  1856    0  50 
Higlltou.     Treatise  on  the  Electric  Telegraph.    12mo.    London,  1852  .  .    0  60 

Hinds  (Dr.  AV.)    The  Harmonies  of  Pliysical  Science  in  relation  to  the  Higher  Senti- 
ments, with  Observations  on  the  Study  of  the  Medical  Sciences,  and  the  Moral  and  Scien- 
tific Relations  of  Medical  Life.    Fcap.  Svo.    London,  1853    .  .  .  .    0  60 

Hoef  er  (F.)    Nomenclature  et  classification  chimiques,  suivies  d'un  lexique  historique  et 
synouymique  comprenant  les  noms  an';iens,  les  forraules,  les  noms  nouveaux,  le  nom  et 
la  date  de  la  decouverte  des  principaux  produits  de  la  chimie.    12mo.,  avec  tableaux. 
Paris,  1845       .  .  .  .  .  .  .  .  .    0  75 

Hoei'er.    Hist,  de  Chimie  depuis  les  temps  les  plus  recules  jusqu'a  nosjours.    2  vols.,  Svo. 
Paris,  1842.    (Very  scarce.)  ....... 

Hood  (C.)    A  Practical  Treatise  on  Warming  Buildings  by  Hot  Water,  on  Ventilation,  &c. 

8d  edition.    Svo.    London,  1866  .  .  .  .  .  .    8  25 

Hoplcins  (T.)    On  the  Atmospheric  Changes  which  produce  Rain  and  Wind.    2d  edit. 

Svo.    .  .  .  .  .  .  .  .  .  .    1  60 

Hopkinson  (J.)    The  Working  of  the  Steam  Engine  Explained  by  the  Use  of  the  Indi- 
cator.   Svo.    London,  1854  .  .  .  .  .  .  .    1  60 

Horsiey  (J.  A.)    A  Catechism  of  Chemical  Philosophy ;  being  a  familiar  exposition  of 

the  Principles  of  Cliemistry  and  Physics.    12mo.    London,  1866  .  .  .2  00 

Houzeau.     Physique  du  Globe  et  Meteorologie.    18rao.,  with  plates.    Brussels,  1864     .    0  68 
HoTward  (i^uke.)    Seven  Lectures  on  Meteorology.    12mo.    London,  1848    .  .100 

Howlett  (HO     On  the  various  methods  of  Printing  Photographic  Pictures  upon  paper, 

with  suggestions  for  their  preservation.    12mo.    London,  1866  .  .  .    0  81 

Hunt  (Robert).    Researches  on  Light.    Svo.    London,  1844  .  .  .    8  00 

Photography:  a  Treatise  on  the  Chemical  Changes  produced  by  Solar  Radiation, 

and  the  production  of  Pictures  from  Nature.    12mo.,  clo.    London    .  .  .175 

Hur«  aux.     Histoire  des  Falsifications  des  Substances  Alimentaires  et  Medicamenteuses, 
precedee  d'une  Instruction  Elementaire  sur  I'Analyse,  et  suivie  des  Essais  et  Analyses 
Qualitatives  pour  Reconnaitre  Instautanemenrt  les  produits  Cliimiques  usites  en  Phar- 
macie,  dans  les  Arts  et  dans  I'Industrie.    1  vol.,  8vo.    Paris,  1856      .  .  .    1  75 

Inorg°anic  Cliemistry  (First  Outlines  of).    12mo.    London  .  .  .    1  25 

Isadore  GeolTroy  Saint-Hilaire.    Lettres  sur  les  Substances  Alimentaires  etpar- 

ticulierement  sur  la  Viande  de  Cheval.    ISmo.    Paris,  1866  .  .  .  .    0  62 

Illustrated  >itandard  Scientific  Works  (Library  of ),  beautifully  printed  and 
illustrated.     Original  London  editions  at  the  price  of  the  Reprints  : 
miullcr's  Principles  of  Physics  and  Meteorology.    With  680  woodcuts  and  2  colored 

engravings.    Svo.  .  .  .  .  .  .  .    4  00 

WeiMbach's  Mechanics  of  Machinery  and  Engineering.    Vols.  1  and  2,  with  900 

woodcuts  .  .  .  .  .  .  .  .    7  50 

Tecl&nolog'y :  or,  Chemistry  applied  to  the  Arts  and  to  Manufactures.    By  Drs. 

Knapp,  Ronolds,  &  Richardson.    Splendidly  illustrated.    8  vols.,  Svo.  .  .  18  00 

Quekett's  Practical  Treatise  on  the  use  of  the  Microscope.    With  Steel  and  Wood 

Engravings.    Svo.    8d  edition,  with  additions  .  .  .  .    5  00 

Graham's  Elements  of  Chemistry,  with  its  applications  in  the  Arts.    2d  edition, 

with  inumerable  woodcuts.    Vol.  I  .  .  .  .  .    3  00 

Fau's  Anatomy  of  the  External  Forms  of  Man.    For  Artists.    Edited  by  R.  Knox, 

M.D.    Svo.,  and  an  atlas  of  28  plates  4to.    Plain,  $6  00.    Colored,         .  .  10  00 

Nichol's  Architecture  of  the  Heavens.     9th  edition.     Entirely  revised.     Steel 

Plates  and  Woodcuts  .  .  .  .  .  .  .    8  00 

mitcliell  (J.)    Manual  of  Practical  Assaying.    2d  edition,  much  enlarged.    Svo. 

London,  1865        .  .  .  .  .  .  .  .    6  00 

Johnson  (J*  F.  AV.)    Instructions  for  the  Analysis  of  Soils,  Limestones,  and  Manures. 

8d  edit.    12mo.     Edinburgh,  1866  .  .  .  .  .  .    0  60 

'  The  Chemistry  of  Common  Life.    2  vols.    12mo.    Edinburgh,  1855  .  .3  00 

U*  JBaiUierej  290  Broadway ^  JT.  K. 


Standard  Scientific    Works, 


Jolinson  (J,  F.  W.)    Elements  of  Agricultural  Chemistry  and  Geology.    12mo.     6th 

edit.    London,  1862       .  .  .  .  .  .  .  .    2  00 

JTonrdaln.    Pliarmacopee  Universelle,  ou  Conspectus  de  toutes  les  Pharmacopees.  2  vols. 

in-6.    2  edit.    Paris,  1840  .  .  .  .  .  .  .    6  25 

Joyce  (Itev.  J.)    Scientific  Dialogues  intended  for  the  Instruction  and  entertainment  of 

young  people.    12mo.    London,  1852         .  .  .  '  .  .  .    0  75 

Dialogues  on  Chemistry.    2  vols.    12mo.        .  .  .  .  .    2  T5 

J  alien.     Quelques  points  de  Science  dans  I'Antiquite.     Physique,  Metrique,  Musique. 

Svo.    Paris,  1854  .  .  .  .  .  .  .  .    2  00 

Ktemtz.     A  Complete  Course  of  Meteorology.    With  additions  by  C.  V.  Wallier.    1  vol., 

post  8vo.,  pp.  624,  with  15  plates.,  cloth  boards.    1345  .  .  .  .    8  00 

Kane  (Sir  Robert).  Elements  of  Chemistry,  theoretical  and  practical,  including  the 
most  recent  discoveries  and  applications  of  tlie  Science  to  Medecine  and  Pliarmacy,  to 
Agriculture,  and  to  Manufactures.    Illustrated  by  20U  woodcuts.    8vo.,  cloth  .  .8  00 

Kemp  (T.  Ij.)  The  Phasis  of  Matter ;  being  an  Outline  of  the  Discoveries  and  Applica- 
tions of  Modern  Cliemistry.    2  vols.     12mo.    London,  1855  ..  .  .  .    6  00 

Agricultural  Pliysiology  Animal  and  Vegetable.     For  Practical  Agriculturists. 

12mo.    Edinburgh,  1S50  .  .  .  .  .  .  .    2  00 

Kerr  (T.)  A  Practical  Treatise  on  the  cultivation  of  the  Sugar  Cane,  and  the  Manufac- 
turing of  Sugar.    12mo.,  cloth     .  .  .  .  .  .  .    1  60 

Knapp,  Ronolds,  and  liicliardson.    Chemistry  in  its  application  to  the  Arts 
and  Manufactures : 

Vol.  I. — Fuel  and  its  Applications — Coal,  Gas,  Oil,  Spermaceti,  Ac,  and  their  applica- 
tion to  purposes  of  Illumination,  Liglithouses,  &c. — llesin.  Wax,  Pe  it.  Wood,  Stoves,  Ac, 
Ac,  in  2  Parts,  Svo.,  witli  433  Engravings  and  4  Plates  .  .  .  .    9  Ot 

Vol.  II. — Glass^  Alum,  Earthenware,  Cements,  Ac,  Ac,  manufacture.    8vo.,  with  214 
Engravings  and  one  Plate  .  .  .  .  .  .  .    4  00 

Vol.  111. — On  those  branches  of  Chemical  Industry,  including  the  Production  of  Food, 
and  Related  to  Agriculture.  (Bread,  Milk,  Tea,  Coffee,  Sugar,  Tobacco,  Ac)  With  9 
Engravings  and  12'J  Woodcuts     .  .  .  .  .  .  .    5  00 

Kobell.     Sketches  from  the  Mineral  Kingdom.    Post  Svo.    London,  1858  .  .    1  60 

Vol.  III.,  embracing  sugar,  cofifee,  tea,  Ac,  with  7  folio  coloured  plates,  .  .    5  OO 

Knigbt.     Dictionary  of  Arts,  Commerce,  and  Manufactures.    Svo.     London,   .  .    2  50 

Kyau  (J.  H.)  On  the  Elements  of  Liglit,  and  their  identity  with  those  of  Matter,  Radi- 
ant and  Fixed.    Svo.    London,  1838  .  .  .  .  .  .    2  00 

Laboulaye.  Dictionnaire  des  Arts  et  Manufactures,  de  I'Agriculture,  des  Mines,  etc. 
Ouvrage  formant  2  tres  forts  volumes  in  4to.,  et  illustre  de  3,000  gravures.  Now  com- 
plete .  .  .  .  .  .  .  .  .  .  15  OC 

J^acauibre.    Fabrication  de  la  Biere  et  Dist'.'latlon  des  Alcools.    Vol.  1  Svo.    (For  the  2 

vols.)  ........  .    5  OC 

JLacan  (E.)    Esquisses  Photographique:;  a  propos  de  I'Exposition  Universelle  et  de  la 

Guerre  d'Orient.     l'2mo.    Paris,  1856         .  .  .  .  .  .    0  75 

liambert.    Sur  la  Meteorologie.    4to.         .  .  .  .  .  .    0  25 

Lame  (Gr.)    Cours  de'Physique  de  TEcole  Polytechnique.    2  vols.,  en  3  Parties.    8vo., 

avec  17  planches.    Paris,  1S36-37.     (Very  Scarce.)  .  .  .  .  6  OC 

Lardner  (I>.)    Handbook  of  Natural  Philosopliy.    Hydrostatics,  Pneumatics,  and  Heat. 

12mo.    London,  1855      .  .  .  .  .  .  .  .    1  50 


The  Museum  of  Science  and  Art.    10  vols.,  12mo.    Illustra/ .;d  by  engravings  on 


wood .  .  .  .  .  .  .  .  .  .    6  25 

-  Handbook  of  Natural  Philosophy  and  Astronomy.  Third  Course — Meteorology  ; 
Astronomy.  8vo.,  with  87  lithograpliic  plates  and  upwards  of  200  li'ustrations  on  wood, 
cloth.    London,  1868      .  .  .  .  .  .  .  .    5  00 

A  Treatise  on  Heat.     12mo.    London,  1856    .  .  .  .  .    1  00 

liassaigne.    Dictionnaire  des  lieactifs  Chimiques  employes  dans  toutes  le  "xperiences. 

8vo.  lig.    P'n-is,  1889      .  .  .  .  .  .  .  .    2  50 

Laurent  (i^l.)    Precis  de  Cristallographie  suivi  d'une  Methode  Simple  d' Analyse  au  cha- 

lumeau.    12mo.     Paris  .  .  .  .  .  .  .    0  87 

Laurent  (Aug.)    Methode  de  Chimie.    Precedee  d'un  Avis  au  Lecteur,  par  M.  Biot.    1 

vol.,  8vo.,  avec  figures  dans  le  tcxte.    Paris,  1854   .  .  .  .  .    2  00 

Laurent  (A.)    Chemical  Method,  Notation,  Cl>'ssification  and  Nomenclature.    Trans- 
lated by  Odling.    London,  1865    .  .  .  .  .  .  .    8  60 

(Cavendish  Society  Publication.) 

Le  Gray.    Nouveau  Traite  de  Photographic  sur  papier  et  sur  verre.    Svo.    Paris,  1851  .    0  T6 

Lehmann.    Physiological  Chemistry.    With  Illustrations.   2  vols.   Svo.    Philadelphia, 

1856, .  .  .  .  .  .  .  .  .  .    6  00 

Chemical  Physiology.    Translated  by  J.  C.  Morris.    Philadelphia,  1856  .  .    2  26 

- Precis  de  Cliimie  Piiysiologique  Anlmale.  Traduction  du  Professeur  Drion.    Paris, 

1855.     I  vol.,  gr.  ISmo.,  avec  fig.  .  .  .  .  ,  .    1  25 

«.  naiUiere,  290  Broadway,  JT.  IT. 


Standard  Scientific  Works. 


li'HcHtier  (S.  I>.)    Traite  de  Chiniie  Pathologique  ou  Recherches  chliniques  snr  les 
f<()li(ie><  ut  les  iiqii'ulea  du  corps  hurnain,  duns  leurri  rai)i)orts  avec  la  Physiologie  et  la 

Pathologie.     8vo.     Paris,  1842     .                .                .                .                .                .                .  2  25 

liC  Noi'inand.     L'art  du  distillateur  des  eaux-de-vie.    2  vols.,  Svo.     Paris,  181T             .  3  00 

liCi  ebours.     A  Treatise  on  Photography,  by  J.  Egerton.     Svo.     London,  1S43                  .  2  50 

liCrebours  et  Secretan.     Traite  de  Photographie.    5e  edit.    8vo.  .               .               .  1  00 

Lievcsque.     Art  of  Brewing  and  Malting.    4th  edit.    Svo.     London,  1847          .               .7  00 
liiebig  (J,  V.)    Chemistry  and  Physics,  In  relation  to  Physiology  and  Pathology.    2d  edi- 
tion.   Svo.        .               .               .               .               .               .               .              .               .  0  75 


Nouvelles  Lettres  sur  la  chimie,  traduites  par  Charles  Gerhardt.    12mo.    Paris, 


1852  .  .  .  .  .  .  .  .  .  .    0  75 

— — — >—    Letters  on  Chemistry.    12mo.    London  .  .  .  .  .    2  00 

Researches  on  the  Chemistry  of  Pood.    Svo.    London.  .  .  .162 

— * Principles  of  Agricultural  Chemistry,  with  special  reference  to  the  late  researches 

made  in  England.    Svo.     London,  1855      .  .  .  .  .  .    1  12 

• Handbook  of  Organic  Analysis,  containing  a  detailed   account  of  the  various 

methods  used  in  determining  the  elementary  composition  of  Organic  Substances.   Edited 

by  Hoffman.     Post  Svo.,  woodcuts.     Loudon,  1868  .  .  .  .  .    1  50 

Liicbig  and  Kopp*s  Annual  Lc'port  of  the  Progress  of  Chemistry,  Ac.    4  vols.,  cloth. 

^85:3.     (To  be  continued. )  .  .  .  .  .  .  .  10  00 

liiS'lftt :  It  Nature,  Sources,  Effects,  and  Applications.   Illustrated  by  a  Photograph.  12mo. 

London, 1856    .  ,  .  .  .  .  .  .  .    1  25 

liOnjS  (r.  A.)  Practical  Photography  on  Glass  and  Paper.  2d  edit.  12mo.  Sewed.  1856.  0  81 
l.ove(T.)    Tli«  Art  of  Cleaning,  Dyeing,  and  Scouring,  &c.    12mo.    London,  1854  .    2  25 

IiO\r  (Da  vi<k.>     All  Inquiry  into  the  Nature  of  the  Simple  Bodies  of  Chemistry,    3d  edit. 

Svo.    London, 1856         .  .  .  .  .  .  .  .    2  75 

LiOVt^i^.     Principles  of  Organic  and  Physiological  Chemistry,  by  D.  Breed.    Svo.    Phila- 
delphia, 1853     .  ,  .  .  .  .  .  .  .    8  50 

MackenKie  (C.)   One  Thousand  Processes  in  Manufactures,  and  Experiments  in  Chemis- 

8vo.    London,  1825.     Half  bd.     .  .  .  .  .  .  .    8  50 

•  '  Theory  and  Experiments  in  Chemistry.    Svo.    London,  .  .  .    6  50 

BIcGauley  (Rev,  .T,  ^V.)    Lectures  on  Natural  Philosophy.    2  vols.    Svo.    London, 

1850.     Half  b.l.  .  .  .  .  .  .  .  .     5  00 

JUalag'Uti  (F.)  Lecons  de  Chimie  Agricole,  Professees  in  1847.  ISmo.  Paris,  1856  .  1  00 
■ (jr.)    Lecons  Elementaires  de  Chimie.    2  vols.    12mo.,  avec  104  figures  intercalees 

dans  le  texte.     Paris,  1853  .  .  .  .  .  .  .    2  50 

Marcet  (W.)    On  the  Composition  of  Food,  and  how  it  is  Adulterated ;  with  practical 

directions  for  its  analysis.     Svo.     London,  1856        .  .  .  .  .    2  00 

marters.    Esquisse  d'une  nouvelle  classification  Cliimique  des  Corps.    4to.         .  .    0  26 

^    Combust:. )n  de  Ja  vapeur  alcoolique  et  etheree,  autour  d'un  fil  de  Platine.    4to,     .    0  z5 

Sur  la  theorie  Chimique  de  la  Respiration  et  de  la  Chaleur  Animal.    4to,  .    0  50 

Martins  (A.)    Handbuch  der  Photographie.    Dritte  aullage.    Svo.    Wien,  1852  .    2  3: 

ITIatlier  (Ja,nies).    Coal  Mines,  their  Dangers  and  Means  of  Safety.    Svo.,  woodcuts. 

London, 1S53    .  .  .  .  .  .  .  .  .    1  12 

mattenci.    Cours  Special  sur  I'Induction,  le  Magnetisme  et  sur  les  relations  entre  la  P6rce 

Magnetique  et  les  Actions  Moleculaires.    Svo.    Paris,  1854    .  .  .  .    1  50 

IVatteucci  et   Savl.     Traite  des  phenomenes  Electro-Physiologiques  des  animaux. 

Svo.    Paris,  1844  .  .  .  .  .  .  .  .    2  00 

]IIatthe'%vs  (W.)     Compendium  cf  Gas  Lighting.    12mo.    London    .  .  .    1  25 

Historical  Sketch  and  Origin  of  Gas  Lighting.    12mo.    London  .  .    2  25 

menioires  d'Agriculture,  d'Economie  Rurale  et  Domestiqne,  publics  et  par  la  Societe  Im- 

periale  et  Centrale  d'Agriculture.    Annee  1854.    lere  partie,  Svo.    Paris,  1855  .    1  50 

Messier.     Observations  sur  les  grandes  Chaleurs,  la  Secheresse,  etc.,  de  la  Seine  a  Paris, 

4to.    Pendant  1793  .  .  .  .  .  .  ,  .    0  50 

Metcalfe  (S.  T.)    Caloric;  its  Mechanical,  Chymical,  and  Vital  Agencies  in  the  Pheno- 
mena of  Nature.    2  vols.,  Svo.     .  .  .  .  .  ,  .  10  50 

Mialhe.    Chimie  appliquee  a  la  Physiologie  et  a  la  Therapeutiqae.    Svo.    Paris,  1855     .    2  6tf 

Miller  (W.  A.)    Elements  of  Chemistry,  Theoretical  and  Practical,  extensively  illus- 
trated.   8  vols.    Svo.    London,  1855^7    .  .  .  .  .  14  00 
Just  Completed. 

Millar  (James).    Elements  of  Chemistry.    Svo.    London  .  .  .    8  75 

Miller  {VV.)    (Cashier  to  the  Bank  of  England.)    Decimal  Tables  used  at  the  Bank  of 

England,  for  reducing  Gross  weight  of  Gold  and  Silver  to  Standard.    4to.    London,  1854    1  25 

Millon  (M.  E.)    Etudes  de  Chimie  Organique  faites  en  vue  des  Applications  Physiolo- 

logiques  et  Medicales.    Svo.    Lille,  1849     .  .  .  .  .  .    0  76 


XT.  Sailliere,  290  Broadway^  JIT.  IT. 


m 


10  Standard  Scientific  Works » 

inillon  (ITf .  E.)    Dea  Plienomenes  qui  se  produisent  du  contact  de  I'Eau  et  du  Ble  et  de 

leur  Consequences,  Industrielles.    8vo.    Paris,  1854  .  .  .  .    0  60 

mitcliell  (•>.)  Manual  of  Practical  Assaying,  intended  for  the  use  of  Metallurgists, 
Captains  of  Mines,  and  Assuyers  in  general.  With  a  copious  table,  for  the  purpose  of 
ascertaining  in  Assays  of  Gold  and  Silver  the  precise  amount,  in  ounces,  pennyweigiits, 
and  grains,  of  noble  metal  contained  in  one  ton  of  ore,  from  a  given  quantity.  1  vol., 
Svo.    2nd  edit.    London,  1854     .  .  .  .  .  .  .    5  00 

• Treatise  on  the  Adulterations  of  Pood,  and  the  Chemical  means  employed  to 

detect  them.    Containing  Water,  Flour,  Bread,  Milk,  Cream,  Beer,  Cider,  Wines,  Spirit- 
uous Liquors,  Coffee,  Tea,  Chocolate,  Sugar,  Honey,  Lozenges,  Cheese,  Vinegar,  Pickles, 
Anchovy  Sauce  and  Pasta,  Catsup,  Olive  (Salad)  Oil,  Pepper,  Mustard.    12mo.    Lon- 
don, 1848  .  .  .  .  .  .  .  .  .    1  50 

Moig^no.    Traite  de  Telegraphic  Electrique.    8vo.,  and  atlas.    Paris,  1852         .  .    8  76 

, Repertoire  d'Optique.    4  vols.,  8vo.    Paris,  1849-50.    (Very  scarce.) 

l^orebead  (•.)    Essay  on  Inebriating  Liquors  and  Distillation.    Svo.    London  .    4  75 

Illorfit  (C)     A  Treatise  on  Chemistry  applied  to  the  Manufacture  of  Soap  and  Candles. 

New  edition.    8vo.,  woodcuts.     Philadelphia,  1856  .  .  .  .    6  00 

mulder  (G,   J.)    The  Chemistry  of  Vegetable   and   Animal   Physiology,  with  intro- 
duction and  notes  by  J.  E.  W.  Johnston,  and  twenty  illustrations,  colored  and  plain. 
8vo.,  cloth        .  .  .  .  .  .  .  .  .    8  50 

niuller.    Principles  of  Physics  and  Meteorology.    Illustrated  with  600  Woodcuts,  and  2 
colored  plates.    8vo.    London,  1847  ...... 

Murphy  (Rev,  R.)    Elementary  Principles  of  the  Theories  of  Electricity,  Heat,  and 

Molecular  Actions.     Part  I.    Svo.    Cambridge  (England),  1832 
Murpliy  (P.)    Rudiments  of  the  primary  forces  of  Gravity,  Magnetism,  and  Electricity 

in  their  Agency  on  the  Heavenly  Bodies.    Svo.     London,  1880 
Murray.    System  of  Chemistry,    4  vols.,  Svo.    London         .... 

Sketch  of  Chemistry.    12mo.    London  ..... 

Manual  of  Chemical  Experiments.    12mo.    London    .... 

Chemical  Tables  and  Diagrams.    Svo.    London  .... 

— — '■ —    Elements  of  Chemistry.    4  vols.,  Svo.    London  .... 

Mnspratt  (Dr.  S.)    The  Use  of  the  Blowpipe,  in  the  Qualitative  and  Quantitative 

Exauiinution  of  Minerals,  Ores,  Furnace  products,  and  other  metallic  combinations. 

By  Platner.    8vo.,  cloth  .  .  .  .  .  .  .    3  00 

Chemistry  Theoretical,  Practical,  and  Analytical,  as  applied  and  relating  to  the 

Arts  and  Manufactures.    Royal  8vo.     Div.  1  and  2.     London,  1856.    Each      .  .    2  62 

Each  division  of  this  fine  work  contains  4  portraits  (engraved  on  steel)  of  the  most 
celebrated  chemists. 

Will  be  completed  in  about  6  divisions. 
Napier  (J.)    Manual  of  Electro-Metallurgy.    Post  Svo.    1853  .  .  .    1  00 

A  Manual  of  the  Art  of  Dyeing.    Svo,  with  illustrations.    London,  1853  .    2  25 

Nesbit  (X,  C.)    On  Agricultural  Chemistry,  and  the  Nature  and  Properties  of  Peruvian 

Guano.    8d  edition.    Svo.    London,  1856  .  .  ,  .  .    1  25 

Nisbet  (W.)    Dictionary  of  Cliemistry.    12mo.    London        .  .  .  .    2  50 

Nicollet  (H.)     Atlas  de  Physique  et  de  Meteorologie  Agricoles.    Grand  in-fol.,  de  13  pi. 

col.,  avec  tableaux  et  texte.    Paris,  1855  .  .  .  .  .  .  13  50 

Noad  (H.  M.)  A  Manual  of  Electricity,  including  Galvanism,  Magnetism,  Diamagne- 
tism,  Electro-Dynamics,  Magneto-Electricity,  and  the  Electric-Telegraph.  4th  edition, 
entirely  rewritten.    Part  I.  Electricity  and  Galvanism.    Svo.     London,  1856  .  .    6  00 

Chemical  Manipulation  and  Analysis  Qualitative  and  Quantitative.     With  an  intro- 


4  00 

225 

4  00 

15  75 

225 

150 

1  00 

750 

duction  explanatory  of  the  general  principles  of  Chemical  Nomenclature,  &c.    Svo. 
London, 1852 


Lectures  on  Chemistry.    8vo.    London 


Normandy.    Commercial  Handbook  of  Chemical  Analysis.    Post  Svo.    London,  1850  . 

A  Practical  Treatise  on  Chemical  Analysis,  Quantitative  and  Qualitative.     By 

Rose.    2  vols.,  Svo.     London,  1848  ...... 

An  Introduction  to  ditto,    Svo.    London       .  ,  ,  ,  . 


Orilla(iT[.  P.)    Elements  of  Modern  Chemistry.    Svo.     London 
«ittley  (iV.  C.)    Dictionary  of  Chemistry  and  Mineralogy.    Svo.    London 
Paris  (J.  A.)     Elements  of  Medical  Chemistry.     Svo,     London 
Paruell.     Treatise  on  Dyeing  and  Calico  Printing.     Svo.     London 


Elements  of  Chemical  Analysis,  Qualitative  and  Quantitative.    Svo.    London.  1845. 


Reduced  to 
Applied  Chemistry  in  Manufactures.     Vols.  1  and  2.    Svo.     London.    Each 


8  00 

8  75 

8  75 

10  25 

2  75 

8  25 

4  UO 

4  75 

2  12 

2  75 

3  75 

Payen.  Cours  de  Chimie  Appliquee,  professe  a  I'Ecole  Centrale  des  Arts  el  Manufactures, 
et  au  Conservatoire  des  Arts  et  Metiers,  lledige  par  Dellisse  et  Poinsot.  Ire  partie : 
Chimie  Organique.    8vo.,  avec  atlas  folio  de  60  planches.     Paris,  1847  .  .    9  00 

MI,  naiUiere,  290  Broadway,  JT.  IT. 


Standard  Scientific  Works,  11 


Payen.  Precis  de  Chimie  Industrielle,  a  I'usag",  des  Ecoles  preparatoires  aux  Profep- 
sions  Industrielles  des  fabricants,  et  des  agriculteurs.  8d  edit.  8vo.,  avec  atlas  de 
planciies  in  8vo.    Paris,  1866       .  .  .  .  .  .  .    4  50 

Payen  et  Ricliard.  Precis  d'Agriculture  theorique  et  pratique.  2  vols.,  8vo. 
Paris,  1861.      ......... 

Peckstoll  (T,  S.)    Treatise  on  the  Manufacture  of  Gas.    8vo.    London 

Peclet  (E.)    Traite  elementaire  de  Physique.  4me  edition.  2  vols.,  8vo.,  atlas,  Paris,  1847 

Traite  de  la  Chaleur,  consideree  dans  ses  applications.    Troisieme  edition  entiere- 

ment  refondue.    Un  atlas  de  122  planches  et  un  vol.  de  texte.    Liege 

Do.,  2  vols.,  4to.,  et  atlas.    Paris  ...... 

Le  supplement  separement,  1863.    4ito.  ..... 


3  75 

7  75 

8  75 

12  50 
17  50 
2  25 

Pelouze.    Traite  de  I'Eclairage  au  Gaz  tire  de  la  Houille,  des  Huiles,  de  Resines,  etc. 

1  vol.,  8vo.,  et  24  pi.    (Scarce.)    ....... 

Pelouz  et  Freiuy.     Traite  de  Chimie  generale,  coraprenant  les  applications  de  cette 

Science  a  I'Analyse  Chimique,  a  I'lndustrie,  a  1' Agriculture,  et  a  I'Uistoire  Naturello. 
2nfle  edit.    Tomes  1  a  5  et  atlas.    Paris,  1854-66      .  .  .  .  .  12  00 

II  y  aura  un  6e  vol.,  qui  sera  donne  gratis. 

Abrege  de  Chimie.    Troisieme  edition,  conforme  aux  nouveax  programmes  de 

I'enseignement  scientifique  des  Lycees.    3  vol.,  grand  18mo.,  avec  174  figures  intercalees 
dans  le  texte.    Paris.  1855  ....... 

— Notions  Generales  de  Chimie.    Un  beau  volume  imprime  avec  luxe,  accompagne 

d'un  Atlas  de  24  planches  en  couleur,  cartonne.    Paris,  1853  .  .  .    5  50 

Peltier     (A.)     Meteorologie.      Observations    et     Recherches    experimentales.      8vo. 

Paris,  1840       .  .  .  .  .  .  .  .  .    2  00 

Pereira.     Lectures  on  Polarized  Light.    Second  edition,  greatly  enlarged  from  materials 

left  by  the  author.    Edited  by  Prof.  Powels,  of  Oxford.    12mo.,  woodciits.    London,  1854    2  25 

PerNOK.  Traite  theorique  et  pratique  de  I'impression  des  tissus.  4  beaux  vol.,  8vo.,  avec 
165  figures  et  429  echantillons  d'etofl"es,  intercales  dans  le  texte,  et  accompagnes  d'un 
atlas  de  10  pi.  4to.,  gravees  en  taille-douce,  dont  4  sont  coloriees.  Ouvrage  auquel  la 
societe  d'encouragement  a  accorde  une  medaille  de  3,000  fr.    Paris,  1846         .  .  17  00 

Pbarmaceutical  JitUfual  and  Transactions.  Vols.  1  to  15.    Half  bound.  London, 

1841  to  1S66      .  .  .  .  .  .  .  .  .  50  00 

Annual  Subscription  (published  monthly)  .  .  .  .  .    3  75 

PbarmacorSBia.     The  New  London,  including  also  the  Dublin  and  Edinburgh  Phar- 

macopseias  by  J.  B.  Nevins,  M.D.     8vo.    London,  1861.         .  .  .  .    5  00 

Pbillipfei  (.J.  A.)  Gold  Mining  and  Assaying;  a  Scientific  Guide  for  Australian  Emi- 
grants.    12mo.     With  woodcuts,  London,  1862.         .  .  .  .  .    1  00 

Manual  of  Metallurgy.     Post  8vo.    New  edit.    London,  1864.    .  .  .    8  75 

Pllill'PS  (Rt)    A  Million  of  Facts  of  correct  data  and  elementary  constants  in  the 

entire  circle  of  the  Sciences,  and  on  all  subjects  of  speculation  and  practice.    New  edit. 
12mo.    1856.     .  .  .  .  .  .  .  .  .    3  62 

Pllilosopliical  Trancactioiis  of  the  Royal  Society  of  London,  from  1825  to  1861, 

inclusive,  forming  25  vols.  4to.     Half  bound  in  Russia  .  .  .  180  00 

(Published  price,  £70  unbound.) 

Picsse  (S.)  The  Art  of  Perfumery,  and  the  Method  of  obtaining  Odors  of  Plants  ; 
with  instructions  for  the  Manufacture  of  Perfumes  for  the  Handkerchief,  Scented  Pow- 
ders, Odorous  Vinegars,  Dentifrices,  Pomatums,  Cosmetiques,  Perfumed  Soap,  &c. 
With  appendix,  &c.    Crown  8vo.,  cloth.     London,  1856.        .  .  .  .    2  25 

Plattner  (<".  F.)  Tableau  de  Caracteres  que  presentent  au  Chalumeau  les  alcalis,  les 
terres  et  les  oxydes  metalliques,  soit  seuls,  soit  avec  les  reactifs.  Traduit  de  I'AUemand 
par  Sobrero.    4to.    Paris,  1848    ,  .  .  .  .  .  .    0  50 

The  Use  of  the  Blowpipe  in  the  Qualitative  and  Quantitative  Examination  of 

Minerals,  Ores,  furnace  products,  Ac.    8vo.    London,  1850  .  •  .    8  00 

Poisson  ($>•  I>.)    Theorie  Mathematique  de  la  chaleur.    8vo.    1885  .  .0  50 

Poll  i  I  let.      Elements   de  Physique  Experimentale  et  de  meteorologie.      7me  edition. 

2  volumes,  8vo.  de  texte  et  un  volume  de  40  pi.  8vo,,  4to.    Paris,  1866  .  .    4  50 
Prechtl  (J.  .1.)    Technologische  Encyclopaedie  oder  alphabetisches  handbuch  der  Tech- 
nologic der  Technischen  Chemie  und  des  Maschinenwesens.    Vols.  1  to  18.    8vo.,  und 
plates  fol.         ......... 

Prideaiix  (T.  S.)    On  Economy  of  Fuel,  particularly  with  reference  to  Reverberatory 

Furnaces  for  the  Manufacture  of  Iron,  and  to  Steam  Boilers.    12mo.,  cloth   .  .    0  80 

Proiit  (W.)    Treatise  on  Chemistry,  Meteorology,  etc.    8vo.  London  .  .    4  50 

Quetelet  (A.)     Positions  de  Physique.    8  vols.  18mo.    Brussels,  1834  .  •    2  00 

Kammelsberg^  (C.  F.)    Lehrbuch  der  Stochiometrie  und  der  Allgemeinen  theoreti- 

schen  chemie.    8vo.    Berlin,  1842  .  .  .  .  .  .    1  75 


Anfangsgrunde  der  quantitativen  Mineralogisch,  und  Metallargisch,  anaytischen 


Chemie  durch  Beispiele  erlautert.    8vo.    Berlin,  1846  .  .  .  .    1  75 


Leisfaden  fur  die  Qualitative  Chemische  Analyse,  mit  besonderer  Rucksicht  auf 


H.  Rose,  Handb.  der  analyt.  Chemie.    8vo.    Berlin,  1843      .  .  .  .    0  76 

jar.  Bailliere,  290  JBroadway,  wT.  K. 


12  Standard  Scientific  Works, 

Raspail  (F.  V.)  Nouveau  Systeme  de  Cliimie  Orpranique,  fonde  sur  de  nourelles 
methodes  d'observations,  precede  d'un  Traite  coniplet  sur  I'art  d'observer,  de  manipuler 
en  grand  et  en  petit,  dans  le  laboratoire  et  sur  le  porte-objet  du  microscope.  Ueiixienie 
ediiion,  entierement  refoiidue,  acconipagnee  d'un  atlas  in-4  de  20  planches  de  figures 
dessinees  d'apres  nature,  gravces  et  coloriees  avec  le  plus  grand  soin.  3  vols.,  8vo.,  atlas 
4to.    Paris,  1888  .  .  .  .  .  .  .      •         .    7  60 


Nouveau  Systeme  de  Pliysiologie  vegetale  et  de  Botanique,  fonde  sur  les  methodes 


d'observations  developpes  dans  le  nouveau  systeme  de  chiune  organique,  accoinpagne 
de  60  planches  contenant  pres  de  1,000  figures  d'analyse  dessinees  d'apres  nature  et 
gravees  avec  le  plus  grand  soin.    2  forts  vol.,  Svo.,  et  atlas  de  60  planches.    Paris, 
1887  .  .  .  .  .  .  .  .  .    7  50 

Le  meme  ouvrage,  planches  coloriees  .  .  .  .  .  12  50 


Reech*    Theorle  Generale  sur  les  Eflfets  Dynamiques  de  la  Chaleur.    4to.,  avec  planche. 

1854  .  .  .  .  .  .  .  .  .    8  00 

Re^naul!  (IH*  H*)    Cours  Elementaire  de  Chimie,  a  I'usage  des  Facultes,  des  Etablis- 

sements  d'Enseignement  secondaire,  des  Ecoles  Normales  et  des  Ecoles  Industrielles.    4 

vols.    12mo.    4th  edit.     Paris,  1853-4        .  .  .  .  .  .    5  00 

■  Elements  of  Chemistry.     Translated  by  Betton   and  Taber.     2  vols.    Svo.    700 

woodcuts.    Philadelphia,  1858      .  .  .  .  .  .  .    7  50 

Relations  des  Experiences  entreprises  pour  determiner  les  principales  lois  et  les 


donnees  nuraeriques  qui  entrent  dans  le  calcul  des  Machines  a  Vapeur.    4to.    Paris, 
1847.    (Scarce.)  .  .  .  .  .  .  .  .  10  00 

■'■  Cours  Elementaire  de  Physique.   4  vols.,  18mo.,  anglais,  avec  figures  dans  le  texte. 

Sous  presse      ......... 

An  Elementary  Treatise  on  Crystallography.    Illustrated  with  108  Wood  Engrav- 
ings, printed  on  black  ground.    Svo.    London,  1848  .  .  .  .    0  76 

Premiers  Elenlents  de  Chimie.    1  vol.,  18mo.,  avec  figures  dans  le  texte.    Paris, 

1850  .  .  .  .  .  .  .  .  .  .    1  25 

Reichenbacb  (Bnron  Charles.)    Physico-Physiological  Researches  on  the  Dyna- 
mics of  Magnetism,  Electricity,  Heat,  Light,  Crystallisation,  and  Cheinism,  in  their  Rela- 
..    tions  to  Vital  Force.   The  complete  work,  from  the  German  .second  edition,  with  additions, 
a  preface,  and  critical  notes,  by  John  Ashburner,  M.D.    Svo.    With  woodcuts  and  one 
plate.    London,  1850     .  .  .  .  .  .  .  .    8  00 

Reid  (D.   If.)    Illustrations  of  the  Theory  and  Practice  of  Ventilation,  with  remarks  on 

Warming,  Exclusive  Lighting,  and  the  Communication  of  Sound.    Svo.    London,  1844  .    4  80 


Rudiments  of  Chemistry,  with  illustrations  of  the  Chemistry  of  Daily  Life.    4th 


edit.    12ino.    London,  1851  .  .  .  .  .  .  .    0  75 

Kepirtoirc  d  r  Pharinacie.    6  vols.    Svo.    1846-1850  .  .  .7  50 

Richardson  (r,  .1.)    Popular  Treatise  on  the  Warming  and  Ventilation  of  Buildings. 

18  plates.     Svo.,  hi.  cf.     London,  1881        .  .  .  .  .  .    2  00 

Riatoul  (  \,  !V.)    A  Guide  to  Painting  Photographic  Portraits,  Draperies,  Background, 

etc.,  in  Water  Color.    With  colored  diagrams.     12!uo.     1855  .  .  .    0  60 

Roberts  (W.  li.)     Scottish  Ale  Brewer  and  Maltster.    Svo.    London  .  .    5  00 

Rob^-rlson  (II.)    A  General  View  of  the  Natural  History  of  the  Atmosphere,  &c.    2 

vols.,  8vo.,  cf.    E«linburgh,  1808  .  .  .  .  .  .    2  00 

Rose  (}l.)  Traite  pratique  d'analyse  chimique,  suivi  de  tables  servant  dans  les  analyses 
a  calculer  la  quantite  d'une  substance  d'apres  celle  qui  a  ete  trouvee  dans  une  autre 
substance;  traduit  de  I'allemand  sur  la  quatrieme  edition  par  A.  J.  L.  Jourdan.  Nou- 
velle  edition,  avec  des  notes  et  additions,  par  M.  Peligot,  professeur  de  chimie  au  Con- 
servatoire des  arts  et  metiers.    2  vols.,  Svo.,  fig.     Paris,  1843 

Practical  Treatise  on  Cliemical  Analysis,  including  Tables  for  calculations  in  Ana- 
lysis.   With  notes  and  additions  by  A.  Normandy.    2  vols.,  Svo.,  cloth.    London  .  10  26 

Analytical  Manual  of  Chemistry,  by  Griffin.    Svo.    London      .  .  .    4  75 

Ausfuhrliches  Handbuch  der  Analytisches  Chemie.    2  vols.,  8vo.,  hf.  bound  calf. 


Braunscliweig,  1851        .  .  .  .  .  .  .  .    8  00 

Roseleitr  (A.)     Manipulations  Hydroplastiques.    Guide  pratique  du  doreur,  de  I'argen- 
teur  et  du  galvanoplastie  (avec  9o  figures  en  galvanoplastie  intercalees  dans  le  texte). 
Svo.     Paris,  1856  .  .  .  .  .  .  .  .    8  75 

Runisrc  (t-'.  F.)    Chemistry  of  Dyeing.    Parti.    Svo.    London  .  .  .150 

Kyiand  (A*)    Treatise  on  Assay  of  Gold  and  Silver  Wares.     Post  Svo.    London,  1852  .    176 
Sabine  (JK.)    Magnetical  Observations  at  Ilobarton.     Vol.  2,  royal  4to.    London,  1S52  .  12  (lO 
Sacc  (('.)    Precis  Elementaire  de  Chimie  Agricole.    2e  edit.    12mo.    Paris,  1855  .     100 

Safety  Lampit  for  Miners,  etc.    Knapp's  Chemical  Technology.    Vol.1.    1856    9  00 
Sanders  (Dr.  J.  Tf.)    Practical  Manual  on  the  Use  of  the  Blowpipe  .  . 

Will  be  published  in  January,  1857. 
Santlni.    Teorlca  degli  objettivi  acromatici.    4to     .  .  .  .  .0  60 

Scheerer  (T.)  An  Introduction  to  the  Use  of  the  Blowpipe  ;  togetlier  with  a  descrip- 
tion of  the  Blowpipe,  characters  of  the  important  minerals.  Translated  by  H.  L.  Blau- 
chard.     12mo.     London,  1856      .  .  .  .  .  .  ,    1  00 

ME.  BaiUiere,  290  Broadway,  JT.  K. 


Standard  Scientific  Works,  13 

Sclioedler  and  ITIedlock.    The  Book  of  Nature  ;  an  elementary  introduction  to  the 

Sciences  of  Pliysics,  Astronomy,  Chemistry,  Ac,  &c.     8vo.     Loudon,  1851         .  .     3  50 

Scbroder  (H.)    Die  Molecularvolume  der  Ohemischen  Verbindungeu  im  festen  und  flus- 

sigen  Zustande.    Svo.    Mannheim,  1843    .  .  ...  .  .    1  00 

Scofferai.     Chemistry  of  the   Imponderable  Agents;  including  the  Principles  of  Liglit, 

Ueat,  Electricity,  and  Magnetism.    8vo.    London,  1856        .  .  .  .    1  00 

Manufacture  of  Sugar  in  tlie  Colonies.    Svo.     London  .  .  .    8  26 


Elementary  Chemistry  of  the  Imponderable  Agents  and  of  Inorganic  Bodies.    Svo. 


London, 1855 
Chemistry  no  Mystery.    12mo.    London 


1  50 

1  50 

8  00 

0  87 

5  00 

1  50 

9  00 

19  00 

6  50 

1  50 

1  50 

fe»core!*by  (  iV.)    Magnetical  Investigations.    8  vols.,  Svo.    London,  1852 

Sheir  (Jolin)*     Directions  for  Testing  Cane- Juice.     12mo,,  cloth 

Suiie«  (A.)    Instinct  and  Reason ;  deduced  from  Electro-Biology.     Svo. ,  cloth  . 

Elements  of  Electro-Metallurgy.    Illustrated  with  woodcuts.    Svo.,  cloth 

Siuitli  (It.  «,)  Italian  Irrigation  ;  being  a  Report  of  the  Agricultural  Canals  of  Pied- 
mont and  Lombardy  ;  addressed  to  tlie  Directors  of  the  East  India  Company.  2  vols. 
Svo.,  and  plates,  folio,  cloth.     Edinburgh,  1855        ..... 

Smith  (W.)    Practical  Dyer's  Guide.    Svo.    London  .... 

Dyers'  Instructor.    12mo.,  London  ...... 

Soily  (E.)    Introduction  to  Rural  Chemistry.    Svo.     London  ... 

Syllabus  of  Lectures  on  Chemistry.    Svo.    London     .... 

Soub«  ira.li.     Traite  de  Pharmacie  tlieorique  et  pratique.    8e  edition.    2  forts  vol.    Svo., 

avec  63  fig.  imprimees  dans  le  texte.     Paris,  1847    .  .  .  .  .    4  00 

Precis  elementaire  de   Physique.    2e  edit.,   augmentee.    1   vol.,  Svo.,   avec    13 

planclies  4to.     Paris,  1844  .  .  .  .  .  .  .    1  25 

Sutton  (  }'.)  The  Calotype  Process :  a  Handbook  of  Photography  on  Paper.  Svo.  Lon- 
don, 1855  .........       75 

Sweden  bor is:.     Principles  of  Chemistry.    Svo.     London     .  .  .  .8  60 

Tables  generales  des  Comptes  Rendus  des  seances  de  I'Academie  des  Sciences,  publiees  par 
MM.  les  secretaires  perpetuels,  conformement  a  une  decision  de  I'Academie,  en  date  du 
13juillet  1835.     Tomes  1  a  31.  3  aout  1835  a  30  decemlire  1S50.    4to.    Paris,  1854 

rra,rdieu  (A.)    Voiries  et  cimetieres.    Svo.    Paris,  1852         .... 

Xa,te  (I",)  The  Little  Philosopiier  ;  or,  the  Science  of  Familiar  Things ;  in  which  the  Prin- 
ciples of  Nature  and  Experimental  Philosopliy  are  Systematically  Developed  from  the 
Properties  and  Uses  of  Familiar  Things.     Vol.  1.     ISmo.     London,  1855 

• (C.)     Theory  and  Experiments  in  Chemistry.    Svo.    London    .  . 

Xbenaid.    Traite  de  Chimie  elementaire.     6 e  edit.    5  vols.    Paris,  1834-6 
Very  scarce. 

Tbiieme  (F.  W.)  Die  Phj'sik  in'ihre  Beziehung  zur  Chemie,  oder  diejenizen  lehren  der 
Physik,  &c.    Svo.    Leipzig,  1840  ...... 

Tbomson  (T.)    Practical  Dyer's  Assistant.    12mo.    London 

Chemistry  of  Organic  Bodies — Vegetables.    1  large  vol.,  Svo.,  pp.  1092,  boards. 

London, 1838   ......... 

Heat  and  Electricity.    2d  edition.    1  vol.,  Svo.    Illustrated  with  woodcuts    Lon- 


don, 1839 

Chemistry  of  Animal  Bodies.    Svo.,  cloth 

History  of  Chemistry.    2  vols.    12mo.    Scarce 

Treatise  on  Brewing  and  Distillation.    Svo.    London 

Elements  of  Chemistry.    Svo.    London         .  . 

First  Principles  of  Chemistry.    2  vols.,  Svo.    London 

Outlines  of  Mineralogy,  Geology,  &c.    8  vols.,  Svo.    . 

System  of  Inorganic  Chemistry.    2  vols.,  Svo.    London 

System  of  Chemistry.    4  vols.,  Svo.     Loudon 


6  00 

1  00 

1  12 

6  50 

75 

1  50 

6  00 

4  00 

4  00 

2  50 

1  80 

3  25 

9  (iO 

9  50 

12  50 

18  00 

Xboni«ou  (R.  ».)  Cycloptedia  of  Chemistry,  Practical  and  Theoretical,  including 
the  Application  of  the  Science  to  the  Arts,  Mineralogy,  and  Physiology.  Svo.,  with 
illustrations.    London,  1854         .  .  .  ,  .  .  .    8  75 

Tborntbwaite  (W.  H.)    A  Guide  to  Photography :  Simple  and  Concise  Directions 

for  obtaining  Views,  Portraits,  &c.    9tli  edit.    12mo.     London,  1856  .  .  .30 

Tizard(W.  L<.)    Theory  and  Practice  of  Brewing.    2nd  edit.    Svo.    London,  1846      .    7  50 
'  Brewer's  Journal.    London,  1854    .  .  .  .  .  .    8  26 

Tolbausen  et  Oardissal.    Dictionnaire  Technologique.    Francais-Anglais-Alle- 

mand.    3  vols.,  12mo.    Paris  1855  .  .  .  .  .  .    5  00 

Tomlinson  (C)  Cyclopaedia  of  Useful  Arts,  Mechanical  and  Chemical,  Manufactur- 
ing, Mining  and  Engineering.  2  vols.,  Svo.,  with  splendid  steel  plates  and  woodcuts. 
Loudon, 1854  .  .  .  .  .  .  .  ,  .  12  00 

JBT.  BailUere,  290  Broadway,  JT.  IT, 


14  Standard  Scientific  Works. 

TroKseau  et  Reveil.    Traite  de  I'art  de  formuler,  comprenant  des  notions  de  Phar- 

macie.    12mo.    1851.    .  .  .  •  •  ...  .    1  35 

Turner  (!•:.)    Elements  of  Chemistry,  including  the  actual  State  and  prevalent  Doctrines 

of  the  Science.    8th  edit.    Edited  by  Baron  Liebig  and  Dr.  Gregory.     8vo.  cloth  .    9  00 

Ure  (A.)  A  Dictionary  of  Arts,  Manufactures,  and  Mines,  containing  a  clear  Exposition 
of  their  Principles  and  Practice.  4th  edit. ,  corrected  and  greatly  enlarged.  2  vols.,  8vo., 
pp.  3,078,  and  1,600  engravings  on  wood,  cloth.    London,  1868  .  ,  .    6  60 

Dictionary  of  Chemistry.    8vo.    London       .  .  .  •  .    6  60 

Van  ITIons.    Sur  les  combinaisons  faites  par  le  Pyrophore.    4to.        .  .  .60 

Violet te  et  Arcliambault.    Dictionuaire  des  Analyses  chimiques  ou  Repertoire 
alpluibetique  des  Analyses  de  tons  corps  naturels  et  artificiels  depuis  la  fondation  de 
la  chimie,  avec  Vindication  des  noms  des  auteurs  et  des  recueils  ou  elles  ont  ete  inserees. 
2  vols.,  Svo.,  a  2  col.    Paris,  1851  .  .  .  .  .  .    4  00 

Or  half  calf  .  .  .  .  .  •  •  •  .    5  00 

"^Valker  ( W.)  The  Magnetism  of  Ships  and  the  Mariner's  Compass :  being  a  Rudimen- 
tary Exposition  of  the  Induced  Magnetism  of  Iron  in  Sea-going  Vessels.  12mo.  Lon- 
don, 1S53  .  .  .  .  .  .  .  .  .     1  50 


(('.  V.)  et.  Fau.    Manipulations  Electrotypiques,  ou  Traite  de  Galvanoplas- 


tie,  contenant  la  Description  des  Procedes  les  plus  Faciles  pour  Dorer,  Argenter,  Graver 

sur  Cuivre  et  sur  Acier,  reproduire  les  Medailles  et  les  Epreuves  Daguerriennes,  Metal- 

liser  les  Statuettes  de  Platre,  etc.,  au  moyen  du  Galvanisme.    4me  edition,  l8mo. 

Paris,  1855        .........       50 

Watson  (K.)    Chemical  Essays.    5  vols.,  18mo.    London,  1800  .  .  .    2  60 

Webster  (J.)    Elements  of  Mechanical  and  Chemical  Philosophy.    Svo.  .  .    8  00 

Weeki'S  (W,  II.)    A  Memoir  on  the  Universal  Portable  Eudiometer,  an  Apparatus 

designed  for  researches  of  Philosophical  Chemistry.    4to.,  with  plate.    Sandwich,  1838  .    1  00 
Weldon  ( W",)     Elements  and  Laws  of  Chemistry.    Svo.    London      .  .  .    3  75 

Wertbeini.    Theses  presentees  a  la  Faculte  des  sciences  de  Paris  pour  obtenir  le  grade 

de  docteur  des  sciences  pliysiques.    Paris  1853         ..... 
Theses  de  physique,  de  chimie  et  de  mineralogie. 
Will  et  Liiebig'.     Manuel   Complet  de   Chimie   Analytique,   contenant  des  Notions 

sur  les  Manipulations  Chimiques,  les  Elements  d' Analy.ee  Iiiorganique  Qualitative  et 

Quantitative,  et  des  Principes  de  Chimie  Organique.    2  vols.     ISmo    .  .  .    1  25 

W^illiaius  (C  W.)    Treatise  on  the  Combustion  of  Coal.    4to.    London        .  .    8  25 

W^itt<«tein.     Practical  Pharmaceutical  Chemistry,  translated  by  S.  Darley.    London,  1853    188 
Woli.t«^r  (F.)    Handbook  of  Inorganic  Analysis.     Translated  and  edited  by  Hofraann. 

12mo.    London  .  .  .  .  .  .  .  .    2  00 

W^rlff  (F.   T.)     Quellen-Litteratur  der    theoretisch-organischen  Chemie,   &c.    SVo. 

Halle,  1845       .......  .  .    1  00 

Woodward  (C.)    A  Familiar  Introduction  to  the  Study  of  Polarized  Light.    2nd  edit. 

Svo.    London,  1851        .  .  .  .  .  .  .  .    1  00 


H.  BAILLIERE  publifhes  a  bi-monthly  Lift  of  all  Works  publifhed  in 
France  and  England  on  SCIENCE,  which  he  will  be  happy  to  fend  gratis  to 
any  perfon  forwarding  his  address,  &c. 

He  alfo  begs  leave  to  call  the  attention  of  Librarians  of  Coljeges,  Profes- 
fors,  and  the  Scientific  World  in  general,  to  his  unfurpafled  facilities  for  the 
procuring  of  Books,  Inftruments,  &c.,  with  economy  and  difpatch,  having 
houfes  in  London,  Paris,  and  Madrid,  engaged  in  the  fame  branch  of  the  bufi- 
ness.  (Duty  free  for  Public  Inftitutions.)  His  ftock  is  always  replete  with  the 
beft  and  lateft  editions ;  from  his  great  experience  and  knowledge  of  Scientific 
Works,  and  from  his  willingness  and  ability  to  give  information  about  both 
old  and  new  books,  he  is  confident  of  being  able  to  give  entire  fatisfaftion 
to  all  who  favor  him  with  their  orders. 

C.  E.  Bailliere,  Agent. 
H.  E.  Bailliere. 


.A.XjDE'ZZ.A.DBXZ'X'XO.^^Zji    xx^'x^xs: 


Alclieniy.    Figuier,  5. 

Apparatus.    An  Explanatory  Dictionary,  1. 

Arts  and  IWanufacturcs.  Acken,  1. 
Brande,  2 ;  Dodd,4 ;  Exhibition  Lectures,  5  ; 
Knight,  8;  Laboulaye,  8;  Maclcenzie,  9; 
Muspratt,  10;  Tomlinson,  13 ;  Ure,  14. 

Assaying-.  Berthier,  2;  MitcheU,  10;  Phil- 
lips, 11 ;  Ryland,  12. 

Blowpipe.  Berzellus,  2;  Griffin,  6;  Mus- 
pratt, 10 ;  Plattner,  11 ;  Sanders,  12 ;  Sheerer, 
12. 

Bre\ving°.  Accum,  1;  Black,  2;  Lacambre, 
8  ;  Levesque,  9  ;  Roberts,  12  ;  Thomson,  13 ; 
Tizzard,  13. 

Caoutcliouc.    Manuel-Roret,  8. 

Chemistry.  Brande,  2  ;  Cavendish  Society, 
8;  Chevallier  (Dictionary),  3;  Cuvier,  4; 
Dalton  (Life),  4 ;  Dumas  (Statique),  5;  Gal- 
loway (Diagram),  5 ;  Griffith  (Recreation), 
6;  Henry,  7  ;  G.  S.  Hilaire,  7 ;  Johnston,  7 ; 
Joyce,  8 ;  Laurent,  8 ;  Lehmann,  8 .  L'Heri- 
tier,  9 ;  Liebig,  9  ;  Low,  9  ;  Mackenzie,  9 ; 
Martens,  9  ;  Messier,  9  ;  Mulder,  10  ;  Mur- 
ray, 10 ;  Orfila,  10  ;  Paris,  10  ;  Pelouze  and 
Fremy,  11 ;  Prout,  11 ;  Rammelsberg,  11 ; 
Reid,  12 ;  Schoedler  &  Medlock,  13 ;  Scofifern, 
12 ;  Smee,  13 ;  Swedenborg,  13 ;  Tate,  13  ; 
Thomson,  13 ;  Watson,  14. 

• Analysis.    Barreswill  &  Sobrino,  1 ; 

Fresenius,  5  ;  Galloway,  5  ;  Gerhaldt,  6  ; 
Johnson,  7;  Liebig,  9;  Noad,10;  Normandy, 
10 ;  Parnell,  10 ;  Rose,  12  ;  Violette  et  Arch- 
ambault,  14 ;  Will  et  Liebig,  14 ;  Wohler,  14. 

■  Animal.    Berzellus,  2 ;  Thomson,  18. 

• Applied.    Ajasson  de  Grandsagne,  1 ; 

Annuaire  de  Chunie,  1 ;  Barruel,  1 ;  Bernay, 
2,  Knapp,  3  ;  Daguin,  4;  Dumas,  5;  Fran- 
coeur,  5 ;  Graham,  6  ;  Kemp,  8 ;  Mialile,  9 ; 
Morfit,  10 ;  Muspratt,  10 ;  Parnell,  10  ;  Payen, 
10 ;  Thomson,  18. 

Agricultural.    Johnson,  8 ;  Kemp, 

8 ;  Liebig,  9 ;  Malaguiti,  9  ;  Memoires,  9  ; 
Nesbit,  10  ;  Payen  et  Richard,  10 ;  Sacc,  12. 

Catecbism.    Graham,  6 ;  Horsley,  7. 

— — —  Cours  et  L.econs.  Boutet  de  Mor- 
vel,  2;  Cabart,  8;  Gerhardt,  6;  Regnault, 


Cbemistry^  Elements  of .  Graham,  6; 
Kane,  8  ;  Miller,  9  ;  Murray,  10 ;  Regnault, 
12  ;  Thomson,  13  ;   Turner,  14 ;  Weldon,  14. 

EHementary.     Cahours,  3 ;  Daguin, 

4;  Pyfe,  5;  Glover,  6;  Gregory,  6 ;  Mala- 
guiti, 9  ;  Regnault.  12  ;  Thenard,  13. 

First  Steps.    Galloway,  5. 

General.    Baudrimont,  1 ;  Berzellus, 

2;  Pelouze  &  Fremy,  11. 

Handbook.     Gmelin,  6. 

History.     Hoefer,  7  ;  Thomson,  13. 

Inorg'a.nic.     Campbell, 3;  Berzellus, 

2 ;  Gmelin,  6  ;  Gregory,  6 ;  Outlines  of,  7 ; 
Thomson,  13. 

Liectures.     Gurney,  6. 

ITI  a,  n  U  a  I  .     Bernay,  2 ;   Brande,  3 ; 

Fyfe,  5 ;  Glover,  6. 

iVlanipulation.  Faraday,  5 ;  Noad 

10;  Benoit. 

jTIemoirs.    Dumas,  5 ;  Graham,  6. 

Non-Metaliir.     Faraday,  5. 

Orsranic.  Brande,  2  ;  Dumas,  5  ;  Ger- 
hardt, 6  ;  Gmelin,  6;  Gregory,  6  ;  Lowig,  9; 
Millon,  9;  Raspail,  12;  Thomson,  13; 
Wolff,  14. 

Philr-sopliy.     Dalton,  4;  Daniell,4; 

Davy,  4  ;  Webster,  14 ;  Weekes,  14. 

Practical.    Bowman,  2. 

Progress  of.      Berzellus,  2;   Liebig 


and  Kopp, 
—  Treatise. 


Gregory,  6. 


Crystailograpliy.  Descloizeaux,4;  Lau- 
rent, 8 ;  Regnault,  12. 

Colors  and  Painting.  Chevreul,3;  Co- 
loriate,  4. 

Cyclopned.ia*  Oooley,  4;  Francis,  5 ;  Pre- 
chtl,  11 ;  Thomson,  1 ;  Tomlinson,  13. 

Dictionary  (Ciieinical;  etc.)  Cheval- 
lier, 3  ;  Crabb,  4 ;  lloefer,  7 ;  Laboulaye, 
8;  Lassaigne,  8;  Nesbit,  10;  Ottley,  10; 
ToUhausen,  13  ;  Ure,  14. 

DistillinK'.  Dubrunfaut,  5 ;  Duplais,  5  ;  La- 
cambre, 8;  Le  Normand,  9;  Morewood,  10. 

Dyeiuiir  and  Scouring:.  Berthollet,  2 ; 
Blanchiment,  2 ;  Brande,  2;  Love,  9  ;  Na- 
pier, 10;  Parnel,  10 ;  Persoz,  11 ;  Kunze,12 ; 
Smith,  13;  Thomson,  18. 


16 


Alphabetical  Index, 


Electricity.  Becquerel,  2;  Chalmers,  8; 
Cummiug,  4 ;  De  la  Rive,  4 ;  De  Bois  Ray- 
mond, 4;  Faraday,  5;  Harris,  7;  Matteuci,9; 
Murphy,  10 ;  Noad,  10. 

Electrlc-Telegrraph*  Highton.T; 
Moigno,  10. 

Electro-metallurgy.  Dorure,  4;  Gal- 
vanoplastie,  5 ;  Gore,  6 ;  Napier,  10  ;  Rose- 
leur,  12 ;  Smee,  18 ;  Walker  et  Fau,  14. 

Falsifications.  Ohevallier,  3 ;  HassaU,  7; 
Hureaux,  7;  Marcet,.9  ;  Mitchell,  10. 

Food.    See  FaUifioaUont. 

Oas.  Accum,  1 ;  Clegg,  4 ;  Knapp,  8 ;  Journal 
of,  6 ;  Matthews,  9 ;  Peckston,  11 ;  Pelouze,  11. 

Geological  Chemistry.    Bischoff,  2. 

Olue.    Colles,4. 

Heat.  Avogrado,  1 ;  Cooper,  4  ;  Dove,  6 ; 
Gavarret,  6  ;  Lardner,  8  ;  Metcalfe,  9  ;  Pe- 
clet,  11 ;  Poisson,  11 ;  Prideaux,  11  ;  Reech, 
12 ;  Regnault,  12 ;  Thomson,  13  ;  Williams,  14. 

Ink.    Encres,  4. 

magnetism.    Becquerel,  2. 

Meteorology,  Arago,  1 ;  Cotte,  4 ;  Hop- 
kins, 7;  Houzeau,7;  Howard,  7;  Kaemtz,8; 
Lambert,  8  ;  Nicollet,  10  ;  Peltier.  11 ;  Pouil- 
let,  11 ;  Prout,  11 ;  Robertson,  12  ;  Sabine,  12. 

mineral  "Waters.    Bouquet,  2 ;  Faure,  5. 

Optics  and  Light.  Biot,  2 ;  Brewster,  8 ; 
Claudet,  4;  Du  Moncel,  5  ;  Gorham,  6;  Har- 
dy, 7 ;  Hunt,  7  ;  Kyan,  8  ;  Light,  9  ;  Moigno, 
10 ;  Scantini,  12  ;  Scoffern,  18. 

Perfumery.    Piesse,  11. 

Pharmacy.  Deschamps,  4;  Goebel,  6; 
Guibourt,  6  ;  Jourdain,  8  ;  Pharmaceutical 
Journal,  11 ;  Repertoire  de,  12 ;  Soubeiran, 
18;  Wittstein,  14. 


Pharmacopeia.  Codex,  4 ;  New  London, 
11 J  Trousseau  and  Reveil,  14. 

Photography.  Barreswil  and  Davanne,  1 ; 
Blanquart,  2;  Brebisson,  3;  Ohevallier,  3  ; 
Cundall,  4;  David,  4;  Delaiiiotte,  4;  De- 
souge,  4;  Disderi,  4;  Fau,  5;  Gaudin,  6; 
Hardwicke,  7  ;  Heath,  7  ;  Henuah,  7  ;  Her- 
ling,  7;  Howlett,  7;  Hunt,  7  ;  Lacan,  8; 
Legray,  8  ;  Lerebours,  9  ;  Long,  9  ;  Mar- 
tens; 9  ;  Rintoul,  12 ;  Sutton,  18 ,  Thorn- 
thwaite,  18. 

Physics.  Aime  Martin,  1 ;  Ajasson  de 
Grandsagne,  1  ;  Archanibault,  1 ;  Biot,  2 
Bird,  2  ;  Boutigny,  2  ;  Brown,  3  ;  Cabart,  3 
Coulomb,4;  Cuvier,4;  Daguin,4;Desains,4: 
Durand,  5 ;  Fau  and  Ohevallier,  5;  Ganot,5 
Grove,  6;  Gruyer,  6 ;  Guitard,6,  Hinds,  7 
Julien,8;  Lame,  8;  Lardner,  8;  Liebig,  9 
McGauley,  9;  Muller,  Id;  Peclet,  11  ;  Pou 
illet,  11  ;  Quetelet,  11 ;  Regnault,  12;  Roichen. 
bach, 12;  Scoffern,  13;  Scoresby,  13  ;  Sou 
beiran,  13  ;  Thieme,  13. 

Platina.    Billard,  2. 

Polarization.  Biot,  2 ;  Pereira,  11 ;  Wood- 
ward, 14. 

Precious  Metals.    Faucher,  5. 

Pyrotecliny.    Chertier,  8. 

Rural  Economy.  Bouchardat,2;  Bous- 
singault,  2. 

Safety  Lamps  for  Miners.    Davy,  4; 

Knapp,  8. 

Sugar.  Baudrimont,  2  ;  Kerr,  8 ;  Scoflfern,  13 ; 
Shier,  13. 

Ventilation.  Amott,  1 ;  Dunn,  5 ;  Hed- 
ley,  7;  Hood,  7;  Mather,  8;  Reid,  12; 
Richardson,  12. 

l¥eaviug'*   Etoffes  Imprimees,  5 ;  Persoz,ll. 


♦      4 


.  •*^99e 


J  St 


^~ 


'  •■•,  --U 


.ilQ(;0 


.U^^^tiJ.  ^„ 


